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The River Severn Case Study - landforms of erosion and deposition

The River Severn Case Study – landforms of erosion and deposition

The River Severn (Afon Hafren) is the UK’s longest river at 354 km (220 miles) long.

The upper, middle and lower course of the River Severn

The source of the River Severn is on the slopes of Plynlimon (the highest point of the Cambrian Mountains) in mid-Wales at around 600 metres above sea level. The hills in this part of Wales receive about 2,650 mm of rainfall annually (compared to the average annual precipitation in the UK, which typically ranges from approximately 800 mm to 1,400 mm). The rain which falls on Plynlimon is stored in thick layers of peat and is slowly released into the River Severn.

Source: https://commons.wikimedia.org/wiki/File:Source_of_the_river_Severn-Tarddiad_Afon_Hafren_-_geograph.org.uk_-_228886.jpg

Rapids on the River Tees in Hafren Forest

Source: https://www.geograph.org.uk/photo/772159

From its source, the River Severn flows over alternating mudstone, siltstone and sandstone layers. The river erodes vertically into its bed by hydraulic action and abrasion . Rapids have formed as the sandstone is more resistant to erosion than mudstone and siltstone.

Around 6km from its source, the River Severn plunges over a narrow band of sandstone at a waterfall called Water-break-its neck (Hafren-Torri-Gwddf). It is located in the Hafren Forest. It has formed due to a layer of harder rock (sandstone) lying over a softer rock (mudstone). The river erodes the mudstone through hydraulic action in the plunge pool. This causes an overhang to form. Eventually, this collapses, and the waterfall retreats upstream, forming a gorge downstream.

Water break its neck waterfall (Hafren Torri Gwddf)

After Llanidloes, the gradient of the River Severn is much more gentle. The river flows east and northeast through mid-Wales, past Newtown and Welshpool and then into Shropshire, where it flows through Shrewsbury and Ironbridge.

There are a considerable number of meanders along the middle and lower course of the River Severn.

OS Map showing meanders at Shrewsbury

The image below shows the River Severn at Shrewsbury.

There are a series of oxbow lakes on the River Severn east of Berriew at the Dolydd Hafren Nature Reserve.

Meanders at the Dolydd Hafren Nature Reserve

Oxbow lakes at the Dolydd Hafren Nature Reserve – Source: Ordnance Survey

Towards the mouth of the Severn, the river becomes very wide. The relief is very flat, where the River Severn flows into the Bristol Channel, forming an estuary . There is significant deposition here, forming large sand and silt banks.

The Lower Course of the River Severn

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Rivers: Case study of the Mississippi Floods, 1993

Use our dedicated case study to learn in-depth about the Mississippi Floods, April to October 1993.

KEY CONCEPTS
FLOOD MANAGEMENT

Introduction

The Mississippi river drains an area of nearly 3 million square kilometres and is the fifth largest river basin in the world. It provides a good case study as there are a range of human and physical causes, huge impacts of flooding and some good examples of effective action taken as a result. The river floodplain is up to 200km wide in the middle stages of the river’s course and as you would expect, there has been a lot of development of the area with much urbanisation taking place. The river has been managed for many years by hard and soft engineering techniques, channel straightening has been used extensively and has reduce the length of the river by 150 miles for example.

The flood was one of the worst in American history with dams bursting, levees being breached and the river remaining at a height above flood level for nearly 150 days. In total, nearly 78,000 square kilometres of land were flooded.

Background essays

Mississippi Flood 1993: Case Study

The Mississippi River, located in North America, begins in Lake Itasca, Minnesota and flows south...

Physical causes:

High rainfall towards the back end of 1992 meant that the soil in the basin was holding more water than usual and in many parts the ground was completely saturated . The soil’s capacity to hold water was therefore very low. There was more snow that usual in the winter from later 1992 to 1993, this built up stores of water that potentially would enter the river during the snowmelt season. From the late spring there were a large number of storms and the area suffered persistent rainfall . As much of the ground was saturated and the water table was high , water entered the river channels very quickly as surface run-off or overland flow. There were huge amounts of rainfall in 24 hour periods across the basin, up to 180mm was not uncommon. Many areas of the basin experienced up to 6 times the usual amount of precipitation. Heavy rainfall in the highest reaches of the snow covered areas of the basin accelerated snowmelt and this had a huge impact on the volume of water entering the channel.

Human Causes:

Shortening of the river’s channel by 150 miles over many years had a cumulative effect of pushing water downstream more quickly, especially during times of peak flow. Extensive dredging had taken place to keep the channel sediment free to improve navigation, the river is a significant part of the transport infrastructure of the USA. 75% of the wetland areas of the river basin had been urbanised impacting on the time taken for water to enter the river system. The wetlands ability to act as a store and release the water slowly into streams and rivers was virtually destroyed. Once flood warning were issued and areas were advised to be evacuated, many people thought that they were not at risk because there were so many protection measures in place. Once the river did flood then there was more damage and danger to people who had stayed in their homes and businesses.

Essays on the causes

'The 1993 Mississippi floods were caused by hard river engineering'. Discuss this statement.

The 1993 Mississippi Flood Report.

Socio-economic

The flood cost an estimated US $15 billion dollars in damages and over 800,000km2 were affected. 30,000 people had no clean water supply until it could be restored by engineers, 72,000 homes were flooded and close to 48,000 were evacuated from their homes. 45 people died as a direct result of the flood.

Flood defences were destroyed completely or damaged. Farmers lost an estimated US $2.5 billion of crops. Much of the flooded farmland was rendered useless for years after the event as it was so badly affected. Infrastructure was seriously affected with roads, bridges, railway and of course river traffic affected. This had a knock on effect to the economy as close to 10,000 were made jobless as a result of their place of work being destroyed.

Environmental

There was a huge loss of natural habitat and wetland areas which were important breeding grounds for bird and animal life having a long term effect on the ecosystem and biodiversity. The habitat for fauna that lives in the water improved due to increased areas of protection and shelter (much like a shipwreck in the sea provides a haven for marine life). Wildlife did have to contend with contaminated water though as chemicals from farms, stores and industry were dissolved into the floodwater. This also affected human drinking water supply.

After the initial flooding there was a lot of standing and stagnant water which attracted insects including mosquitoes, and rats were a problem in some areas.

Flood management since 1993

Since the flooding subsided the US government prioritised the management of the area affected and much engineering has taken place to try and reduce the risk of future flooding. The 6 very large dams built along the Mississippi’s main channel have been added to by building more on the tributaries. There are 9 dams on the Tennessee (a major tributary of the Mississippi) and a further ten on its own tributaries.

A series of 105 reservoirs have been linked to control the risk of flooding by controlling the flow of water through them.

Afforestation has been prominent in some areas to slow down the rate at which precipitation or snowmelt enters the channel system.

Although straightening and shortening of the river added to the problems of the 1993 flooding, more of this has been done and engineers have learned from previous experience. Levees have been reinforced with concrete rather than more natural and weaker methods (soil for example) and raised to more than the level of the 1993 flood waters. These levees provide protection for 1000’s of settlements along the Mississippi’s course.

Essays on the impact

Flooding on the Mississippi

River Management Case Study on The Mississippi.

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River management: a case study of the River Severn

In this unit you’ll compare hard and soft engineering methods for managing the flood hazard on the River Severn.

Then try the quiz to see how much you know about river management and measures put in place to help manage the risk of floods.

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5.2.4: Colorado River Case Study

Last updated
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Page ID 48216

Heather Karsten & Steven Vanek
Pennsylvania State University via John A. Dutton: e-Education Institute

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Flow Depletion and Salinity

The Colorado River in the southwestern U.S. is an excellent case study of a river that is highly utilized for irrigation and agriculture. A majority of the Colorado River’s drainage basin has an arid or semi-arid climate and receives less than 20 inches of rain per year (Figure 4.2.5), and yet the Colorado River provides water for nearly 40 million people (including the cities of Los Angeles, San Diego, Phoenix, Las Vegas, and Denver) and irrigates 2.2 million hectares (5.5 million acres) of farmland, producing 15 percent of U.S. crops and 13 percent of livestock (USBR 2012). Much of the irrigated land is not within the boundaries of the drainage basin, so the water is exported from the basin via canals and tunnels and does not return to the Colorado River (Figure 4.2.6).

The net results of all of these uses of Colorado River water (80 percent of which are agricultural) in both the U.S. and Mexico are that the Colorado River no longer reaches the sea, the delta is a dry mudflat, and the water that flows into Mexico is so salty as a result of agricultural return flows that the U.S. government spends millions of dollars per year to remove salt from the Colorado River.

Many farmers in the Colorado River basin are working to use Colorado River water more efficiently to grow our food and food for the animals that we eat. Watch the video below and answer the questions to learn more about farming in the Colorado River basin.

Figure 4.2.5. : Average annual precipitation of the Colorado River basin. Data are United States Average Annual Precipitation, 1961-1990 published by Spatial Climate Analysis Service, Oregon State University; USDA - NRCS National Water and Climate Center, Portland, Oregon; USDA - NRCS National Cartography and Geospatial Center, Fort Worth, Texas. Credit: Map by Gigi Richard

Figure 4.2.6. : Map of the Colorado River basin showing areas outside of the basin using Colorado River water Credit: USBR 2012

Check your Understanding

Watch the following video then answer the questions below

Video: Resilient: Soil, water and the new stewards of the American West (10:13)

Resilient: Soil, Water and the New Stewards of the American West

National Young Farmers Coalition

Narrator: A drop of water from a sprinkler on a quiet Los Angeles street. A shower head in a Las Vegas hotel. Agricultural land in California's Imperial Valley. Where does all this water come from? The Colorado River. In 1922, representatives from seven states gathered at Bishop’s Lodge New Mexico to sign the Colorado River Compact, an agreement on how to allocate water in this precious river system. But that River had more water then, than it does today. The Colorado River Basin touches the lives of every American. The river system runs through seven states in the US, and two in Mexico, and supplies water for over 36 million people. It also irrigates over five million acres of cropland and provides eighty percent of our winter produce, all from one river. And agriculture is the first to feel the pressure. At the headwaters of the Colorado River, farmers and ranchers are creating a toolbox of resilience. They save water with efficient technology and by building healthy soil.

Brendon Rockey, Rockey Farms, Center, Colorado: My grandpa always had a philosophy on this farm that you have to take care of the soil before the soil can take care of you, and he just felt like we had gotten away from that. That's the number one thing with everybody. is yield, yield, yield. Everybody wants just big production, you know, so that's why you want to dump on the fertilizer, kill off anything that poses a threat. It's all about production. We put more of an emphasis on quality. And what's really nice is when you put the emphasis on quality, the quantity usually comes along with it.

Narrator: And he also uses less water. How? By managing his soil more efficiently and working with nature instead of against it. Brendon rotates his potato crops with green manure, or cover crops, that enhance soil health while reducing his dependence on pesticides, fertilizers, and water.

Narrator: Unhealthy soil lacks life. Often a crust forms on its surface. When a crop is watered, very little soaks into the soil. Instead, it sits on top and is left to evaporate or run off. This land often has to be watered more frequently to get water to the crops. Healthy soils teem with life and are often built when farmers plant a mix of cover crops that add nutrients to the soil. When these plants die they become organic matter which helps store water in the soil. That means farmers can irrigate less, and have more certainty in times of drought.

Brendon Rockey: The reason we got into cover cropping was a response to a drought. Now that we've brought in more diverse crops, that have diverse root systems, which actually help benefit the water use efficiency as well, we've regenerated the soil to the point now where I'm growing a potato crop on about 12 to 14 inches of irrigation water per year. We're focusing on the soil, we're investing in the soil and we're bringing up for the functionality of the soil back to its optimum range.

Mike Jensen, Homegrown Biodynamic Farm, Bayfield, Colorado: A farm after 20 years should have much better soil than when it started. The best thing I do for my land is cover cropping. It rejuvenates the soil keeps everything happy, gets all the flora and fauna in balance. It's not about production this year, it's about production for the next 30 years.

Mike Nolan, Mountain Roots Produce, Mancos, Colorado: One thing I've learned from a bunch of folks, old-timers I've worked with is, do your best to not ever have any bare ground, nothing open, no open soil. I mean even in nature, even in the desert, technically there are things covering the ground. There's things, fungi and bacteria, that are holding the ground together. So what I did about three weeks ago is I planted out this oats crop. I’m not gonna harvest this for the seed or anything, but what it's going to do, it's going to hold moisture in here.

Cynthia Houseweart, Princess Beef Company, Hotchkiss, Colorado: Right now we're in full bloom, but what I like to see is a variety of plants. I don't want to just see straight alfalfa, I want to see grass and, and clover. I don't want bare ground. If we didn't have irrigation water, we would be a desert. This would be sagebrush, cedar trees. This, the water is what creates our livelihood. We graze during the growing season. So the conventional thing is, you move your cows off your pastures, grow them and cut them for hay. What we do instead of cutting them for hay, we graze them.

Narrator: Cynthia waters, using a center pivot. As it moves across her fields, the cattle follow behind eating fresh grass.

Cynthia: And the things they trample in, and their manure, adds to the soil, feeds the soil. It breaks down, turns into humus. The soil becomes more like a sponge and can suck up water that we put on it and rain, so the soil improves, which means the plants grow better and then our cows look better.

Dan James, James Ranch, Durango, Colorado: When you build topsoil, you increase the capillary action of the soils ability to retain water; and the less frequent you're applying your water, the more those roots have to go after that water, as it recedes into the ground. And so now you have all these roots below the surface, and all of a sudden here comes your cow. She comes in and she clips that off. Now your plant’s this high and the plant sheds the same proportion of roots. Now you're adding organic material and you're growing topsoil.

Strengthening the soil is also a concern of Steve Ela, a fruit grower in Hotchkiss Colorado. With precise tools like micro sprinklers and permanent drip irrigation, Steve can use water precisely when and where he needs it most, and his soil is healthy enough to efficiently deliver that water to his crops.

Steve Ela, Ela Family Farms, Hotchkiss, Colorado: For us on the farm it's the difference between using first furrows and the micro specters and now drip. It’s been a bit of an evolution of thinking. So for me it's been, it's not that really one system is better or worse, but it's an evolution of thinking, of trying to manage our water better, trying to use the system of irrigation management and cover cropping to manage our weeds, and also to just only to grow better fruit and healthier trees. Yes, it's expensive on the upfront cost, but it's a system then we can use for 20 years. It's very efficient. I think it probably saves us that much, you know, in water.

Narrator: It's innovation that saves water and money, while increasing soil fertility. It's also innovation that includes technology. Water data delivered by weather satellites, GPS, and even smart sensors like those used by Randy Meaker, a Colorado wheat and corn grower. He uses cover crops to improve his soil and by monitoring soil moisture, he can more effectively use the center pivots to reduce water use.

Randy Meaker: There are huge efforts going on right now, trying to figure out how we and the western United States can solve the shortages of water due to drought conditions. There's two ways to keep water in a bucket and one is to put more water in at the top, the other one is to take less water out at the spigot. People in the lower Basin States, where the population centers are, they're looking for us to supply them more water. But what we're looking for is a responsible use from them. What good is it for me to be restricted if I realize that we're still irrigating lawns, we're still washing cars.

Narrator: Water is the lifeblood of our Western landscape. Farmers and ranchers are as essential to it as the water itself. The water challenges these farmers face are many, but across the country they gather to share their water knowledge and provide each other with valuable support. They build community and grow good food, while stewarding both their land and their water. They are the water stewards of the Colorado River Basin.

Knowledge Check (flashcards)

Please take a few minutes to think about what you just learned, then consider how you would answer the questions on the cards below. Click "Turn" to see the correct answer on the reverse side of each card.

Front: How does the Colorado River touch the lives of nearly every American?

Back: 80% of winter produce in the US are grown with Colorado River water (in 2014)

Front: What practices are introduced in the film that can increase water use efficiency when growing irrigated crops?

Back: Center pivot, Microspray and drip irrigation, Cover crops, Soil health

Front: How can healthy soil reduce the amount of water used to grow crops?

Back: Healthy soils can be more permeable and can store more water and so more water soaks into the ground and is stored in the soil. Water in the soil is available to the plants. Increases ability of soil to retain water.

Front: How do cover crops help conserve water?

Back: Cover crops help improve soil health (see the previous answer).

Case Study: American Rivers

Increasing Community and Ecological resilience by Removing a Patapsco River Fish Barrier

Key information.

Transferable Strategies
Project Overview

Challenges and Solutions

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1 The award amount does not necessarily reflect the total project cost. The match amount is based on the project proposal information. 2 Disclaimer: The opinions expressed in the multimedia and additional relevant links are those of the project team and their partners only and do not necessarily reflect the views of the National Fish and Wildlife Foundation (NFWF).

Transferable Strategies from this Case Study

Demonstrate project effectiveness: By collecting data on project impacts and engaging in ongoing communication, a team can help regulators and permitters understand the proposed project approach. When feasible, conducting pilot or demonstration projects can also show effectiveness.
Consider opportunities for adaptive management during project development and design: Adaptive management can effectively reduce the potential for an over-engineered project, help lessen long-term project costs, and contribute to more enduring project outcomes.

Project Overview: Increasing Community and Ecological Resilience by Removing a Patapsco River Fish Barrier

Restored Bloede Dam project site (Interfluve).

After years of hard work by American Rivers and its project partners, the Bloede Dam in Maryland’s Patapsco River was successfully removed in 2018, restoring the river’s natural flow and native fish spawning habitat. Removing the dam also strengthened community resilience, improved public safety, and facilitated increased sediment transport to marshes and beaches along the Chesapeake Bay.

Bloede Dam, built in 1906, had a hollow structure that allowed turbines to function inside, making it the first underwater hydroelectric dam in the world. The dam provided electricity to surrounding communities until it ceased producing power in 1924 due to challenges associated with maintaining efficient power production. Bloede Dam, whose ownership was transferred to the Maryland Department of Natural Resources in 1938, blocked fish access to native habitat and spawning grounds in addition to being costly to maintain and dangerous to swimmers and recreationalists on the Patapsco River.

Restoration in progress at Bloede Dam (Serena McClain).

Perhaps even more challenging was obtaining permits to restore the river to its natural state with minimal intervention. The team encountered difficulties obtaining permits for this approach since the state was more accustomed to using traditional engineered approaches such as bank hardening and channel construction. The project team used a combination of demonstration projects, predictive modeling, and adaptive management to overcome this challenge.

Policy and Institutional Constraints

Challenge:

The project team proposed to remove the defunct dam, thereby restoring natural river and sediment flows. Regulators were concerned that reestablishing sediment flow might result in over-sedimentation of Baltimore Harbor and the Chesapeake Bay.

Use an adaptive management approach: Early in the project, the team developed an adaptive management plan with a proposed approach for the dam removal along with potential risks and setbacks, as well as options for addressing them. Regular monitoring of the system allowed the project team to track sediment movement patterns, which helped the team determine that no additional interventions were required downstream, saving valuable time and resources.
Use experts: To ease regulators’ concerns over potential downstream over-sedimentation, the team brought in sediment experts, who concluded that any short-term impacts of a sediment release would likely be negligible compared to the long-term benefits of a free-flowing and naturally functioning river.
Build on previous project experience and knowledge: American Rivers had previously been granted demonstration permits for two other dam removals along the Patapsco River. These efforts helped showcase the benefits of the project and proposed approach to regulators. Having this experience also helped American Rivers navigate the regulatory framework and prepare for potential regulatory hurdles, in addition to providing valuable lessons to inform future dam removal and river restoration projects.
Conduct monitoring and modeling: As part of previous dam removal projects, American Rivers and its partners established robust, long-term monitoring efforts to study how rivers respond both physically and biologically to dam removal. These monitoring data, combined with predictive sediment transport modeling, helped to illustrate and contextualize the relatively low risks associated with removing the Bloede Dam

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River histories: a thematic review

Published: 13 February 2017
Volume 9 , pages 233–257, ( 2017 )

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Paula Schönach ORCID: orcid.org/0000-0001-8659-8012 1

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This review discusses contemporary river history literature of the past two decades. It presents an introduction to the evolution of river history literature and discusses its relation to the scholarly field of environmental history. The review argues that the study of river histories is increasingly sophisticated methodologically, particularly in interdisciplinary breadth and comparative approaches. This article concentrates on selected studies of European and North American rivers during the nineteenth and twentieth centuries and discusses the recent literature on river histories within three thematic frames. First, this paper discusses the spatial dimensions and different spatial scales of river histories, especially rivers as connectors and dividers. The second theme presents three different types of power relations in human–river interaction. Third, this paper will touch upon the temporal questions of river biographies. This review will pay special attention to the growing literature addressing the attempts to re-establish environmentally sound human–riverine relationships and improve the status of rivers through restorative activities. This article shows that a thematic analysis of contemporary river history offers a fruitful frame to understand the complex and intertwined nature of the temporal, spatial, and power-related dimensions in the narratives.

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Reclaiming Rivers from Homogenization: Meandering and Riverspheres

Truths of the Riverscape: Moving beyond command-and-control to geomorphologically informed nature-based river management

Historic Milestones of Human River Uses and Ecological Impacts

Ackroyd’s ( 2007 ) colossal and multi-layered work on the “sacred river” Thames serves as a European example, while Talbott’s ( 2009 ) piece on the Hudson River shows how the readership of river histories is widened to new audiences, children in this case.

Some monographs and edited volumes on river histories include more rigorous introductory or concluding chapters with reflections on conceptual and thematic choices and their methodological implications in the historiography (Mauch and Zeller 2008 ; Pritchard 2011 ; Castonguay and Evenden 2012a , b ; Coates 2013 ). But they draw mainly on the work presented in the edited volumes in question or the thematic subfield of the respective book.

I prefer the term field rather than discipline as a divergence from the institutional connotations of discipline . Scholarly field better includes the multiplicity of possible approaches and scholarly traditions applicable in environmental history, which, despite the flourishing scholarship, is still not an academically established discipline in many countries. See Huutoniemi et al. ( 2010 ). For the development of the field in general, see e.g. Hughes ( 2006 ).

This dynamism is reflected in the amount of non-western river history publications. As a key contribution, Volume 1 in the Water History Series (Eds. Tvedt and Jakobsson 2006a ) offers an extensive selection of river history cases from all inhabited continents, and predominantly from the non-western world. For the Latin American perspective, see Cleary ( 2001 ) for a review of the environmental history of the Amazon.

The main sources have been the major journals in the field, Water History, Environmental History, and Environment & History. While the thematic foci of this paper guided the choice of monographs for the analysis, it was to some degree influenced by the significance of some works within the field, indicated by citations, and occasionally limited due to resources and availability. Additionally, I have included some works published in less common languages (Finnish and Swedish).

For the sake of clarity, I use river as an overarching term, including main rivers, tributaries, and smaller creeks as well, while being aware that river terminology is variable and differently defined according to linguistic, scientific, or historical contexts. The appropriate terms may vary by the discharge of the river, the navigability of the river, the size of its catchment area, its geographical location (e.g. in the Swedish language rivers north of the Göta älv and Dalälven are called älv, south of them å or ström, and rivers outside of Scandinavia are called flod ), or other criteria.

European scholars with their linguistic diversity balance local significance and audience and international accessibility to their research against international academic publishing with an English language dominance. Since article-length contributions can cover only a very small and specific part of river history, terming them “environmental history of river X”, which implies comprehensive coverage of complex histories, may seem inaccurate to scholars. Special journal issues focusing on one river and successfully exemplified by the “Danube-issue” of Water History (Vol 5, issue 2, 2013), proves to be one recommendable alternative to bridge these challenges.

I use the term interdisciplinarity as an overarching term for different kinds of research activities that include at least two research fields, in whatever degree of interaction and relatedness, and I will not elaborate on the distinct conceptualizations of interdisciplinarity (e.g. multidisciplinarity, transdisciplinarity, etc.) See Huutoniemi et al. ( 2010 ). For a discussion on the possibilities and challenges of interdisciplinarity in environmental history see Hamilton et al. ( 2011 ).

These are based on typologies for the field of environmental history as presented by Massa ( 1991 ), McNeill ( 2003 ), and Mosley ( 2010 ).

Massa ( 1991 ) classifies the political sphere as a distinct, fourth category that also includes changes in the institutional structures.

Henshaw ( 2011 ) used the term “River of Inspiration” in his work on the Hudson River somewhat earlier but lacked more detailed elaboration on the nature of this “inspiration”.

Science, Technology and Society-studies, which itself is an interdisciplinary subject.

Special Issue of Water History Vol 5, issue 2 ( 2013 ).

Developed by urban environmental historian Tarr ( 2002 ), and applied by e.g. Barles ( 2007 , 2012 ) for the Seine study and Gierlinger et al. ( 2013 ) for the Danube.

In a rare example from non-western rivers, Hoag ( 2013 ) uses the insights from several African rivers (Rufiji, Gambia, Volta, Niger) to explore and explain continuities in African development and the related colonial legacies.

The adjacent articles on each case comprise a special edition of Water History 8(3):2016.

Several histories of earlier periods show that human induced alterations of riverine environments are by no means an invention of the late modern period nor exclusive to the North American or European spheres (see Wilson 2010 ; Hoffmann 2010 ). However, the scale and geographical extent of human activity constitute a landmark of the modern exploitation of rivers.

While the issue of cooling water used for the generation of electricity has been addressed by some scholars (e.g., White 1995 , p. 81; Pritchard 2011 ), it has so far remained a somewhat neglected topic in environmental river histories.

She credits Steinberg’s ( 1991 ) work for influence in the development of the concept.

A panel at the congress of the American Society for Environmental History in 2014 was titled ‘Rivers with bad habits’.

See special issue of Environment and History 19 (2), 2013.

Acknowledgements

This study was funded by the Helsinki University Centre for Environment (Multidom-project) and the Academy of Finland (Grant Nos. 263305 and 286676).

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Paula Schönach

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Schönach, P. River histories: a thematic review. Water Hist 9 , 233–257 (2017). https://doi.org/10.1007/s12685-016-0188-4

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DOI : https://doi.org/10.1007/s12685-016-0188-4

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We safeguard and restore wetlands for people and nature

Case study: River Restoration – River Glaven

The EU Water Framework Directive (WFD) advocates for the protection and restoration of rivers, lakes, groundwater bodies and riverine wetlands. There is a demonstrable impact of the WFD in terms of water quality improvement in Europe, mainly at a local scale.This case study of the River Glaven in the UK demonstrates improvements in the ecological conditions thanks to local restoration measures. It also illustrates that to improve water quality at water body scale, more actions are needed; including larger-scale river restoration measures and a catchment-based approach to reduce pressures and to have an impact on the entire water body. Moreover, an expansion of the monitoring is needed to detect improvements in adjacent wetlands and better reflect on the effects of restoration measures.

The River Glaven has historically been modified for industrial purposes and to protect the adjacent floodplain farmland. Water control structures such as weirs and sluices, together with canalisation and embankments have left the River Glaven severely modified. The connectivity between the river and its floodplain has been reduced further in the 1970s to the 1980s through dredging of the channel and draining of the floodplain. In order to reach the EU Water Framework Directive objective of “good ecological status”, river restoration measures are needed. This case study elaborates on the chosen restoration measures, the short term results and the gained insights.

Restoration measures were considered that improved the form of the river and connectivity to the floodplain. Restoration at the severely modified and disconnected Hunworth Meadows took place in 2 phases: during the first phase in 2009, around 400 m of embankments were removed resulting in a 40–80 m wide floodplain area (3 hectares). A second phase of work was conducted in 2010 to improve the river morphology. The intervention created a narrower and geomorphologically more diverse and meandering channel, with an associated increase of river sinuosity by 16%.

Re‐meandered reach of the River Glaven at Hunworth: In January 2009, prior to the rehabilitation project, on the left, and in December 2010, after re‐creation of meanders on the right[1].

Embankment removal and re-meandering alongside the River Glaven at Hunworth had positive effects for the river–floodplain ecosystem functioning. Short term results included:

A significant increase in macrophytes’s richness;
Limited impact on stream invertebrate biodiversity;
A significant increase of invertebrate biodiversity in backwaters along the floodplain[2];
An increase of the density and biomass of brown trout ( Salmo trutta ), but no significant short-term impact on other fish populations[3];
A moderate but detectable effect on flood peak attenuation, owing to the limited length of restoration[4], and improved free drainage into the river.

A significant aspect of this project is the inclusion of 6 backwaters in the monitoring plan that allow a more appropriate and detailed evaluation of the ecological conditions of the whole river corridor. This is very often not the case, as sampling sites are generally located along the main channel, and side channels and backwaters are not considered within the sampling protocol[5].

Another shortcoming in most restoration projects is the solely monitoring of Biological Quality Elements (BQEs) to define the ecological status of rivers. Recent studies showed that although the BQE-based metrics and indices are sensitive to water quality alteration and general habitat degradation, their response to hydromorphological degradation is generally weak or absent[6]. The monitoring plan of the River Glaven included additional bioindicators such as dragonflies and amphibians, through which the hydromorphological impact might be better understood[7].

This case study demonstrates positive results in the improvement of the ecological conditions of the restored river reaches. This case study also points out that an implementation gap still remains between current restoration measures and the actions required to improve ecological conditions at water body scale. To achieve the WFD objectives we need interventions of a larger scale to make a difference for the “good ecological status” of the water body. Furthermore, numerous studies have shown that localised river restoration does not necessarily translate into significant improvements in biodiversity[8]. One factor that is not addressed by reach‐scale rehabilitation is the influence of catchment‐scale pressures on rivers. To have positive outcomes for bioindicators, site-based measures should be combined with addressing pressures upstream. An integrated catchment approach should be thus applied.

These insights should help water managers develop more effective restoration measures and monitoring tools. The River Glaven case study is part of a larger case study report with more examples of river restoration measures and their contribution to WFD objectives.

[1]Champkin et al., 2018
[2]Sayer 2014
[3]Champkin et al., 2018
[4]Clilverd et al., 2016
[5]Golfieri et al., 2018
[6]Hering et al., 2006; Friberg et al., 2009; Marzin et al., 2012; Dahm et al., 2013
[7]Munné et al., 2003; Jähnig et al., 2009; Gumiero et al., 2015, Sayer, 2014; Simaika and Samways, 2009
[8]Palmer et al., 2010

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ICESMART - 2015 (Volume 3 - Issue 19)

River water pollution:a case study on tunga river at shimoga-karnataka.

Article Download / Views: 3,224
Total Downloads : 16
Authors : Dr. H. S. Govardhana Swamy
Paper ID : IJERTCONV3IS19035
Volume & Issue : ICESMART – 2015 (Volume 3 – Issue 19)
Published (First Online): 24-04-2018
ISSN (Online) : 2278-0181
Publisher Name : IJERT

Dr. H. S. Govardhana Swamy

Professor & Head, Department of Civil Engineering RajaRajeswari College of Engineering,

Bengaluru, India

Abstract Tunga River has been one of the most prominent and important river of Karnataka in Shimoga District. Unfortunately, certain stretches of River Tunga are much polluted. Various urban centers are located on the banks of Tunga River, draw fresh river water for various activities. In almost the entire wastewater generated by these centers is disposed off into the river. The objective of the monitoring studies undertaken for water body is to assess variation in water quality with time. Four sampling stations were selected along the river for sampling purpose from August 2013 to August 2014.Water samples were analyzed in terms of physico-chemical water quality parameters.

Keywords Thunga River, water quality, point pollution, Physico-chemical parameters

INTRODUCTION

In nature, water is the essential fluid from which all life begins. All living things need water to maintain their life too. In domesticity, it is very useful, such as for washing and cleaning. In industry, it is the common solvent for Paper and water, textile and electroplating. Besides, the generation of electricity also requires water. It has many uses. However, it can be easily polluted. Pollutants deteriorate the quality of the water and render it unfit for its intended uses [1]. The pollution of rivers and streams with chemical contaminants has become one of the most critical environmental problems of the century. It is estimated that each year 10 million people die from drinking contaminated water. Water is one of the most common and precious resources on the earth without there would be no life on earth [2]. Pollution is a serious problem as almost 70% of Indias surface water resources and a growing number of its groundwater reserves have been contaminated The quality of water is described by its physical, chemical and microbiological characteristics. Therefore a regular monitoring of river water quality not only prevents outbreak of diseases and checks water from further deterioration, but also provides a scope to assess the current investments for pollution prevention and control. In this study, seasonal variations of physico-chemical and bacteriological characteristics of water quality in Tunga river was assessed in Shimoga town in Karnataka.

MATERIALS AND METHODS

Shimoga is town, situated between the North and South branches of river Tunga. It is located on the Bangalore Honnavar highway.Though it is a town of medium population, the temples and historically significant monuments of this town attracts a large number of tourist people resulting in a very high floating population. Because of this reason the river Tunga along Shimoga town stretch is prone to anthropogenic activities such as bathing, washing and disposal of wastes. The ground level in the town slopes towards river so that most of the storm and sewerage drains discharge into river Tunga. There are two stream monitoring stations and 15 drains located in this town stretch

Monitoring Stations

Station – S1

Station S1 is located on the north side of the river, near the Shimoga Thirthahalli new bridge. It is an upstream station and near this station water is being drawn for supply to the town.

Station – S2

This station is about 300 m downstream of station S1.The station S2 is located on a drain that enters the river from the industrial town areas. The flow in the drain is mainly comprised of industrial waste.

Station – S3

The station S3 is an most affected station and is positioned near the Vinayaka temple(Ramanna shetty park). It is downstream of the sewage disposal point from the station S3. A bathing ghat exists near this Station.

Station S4 is located on the south side of the river, near the Shimoga Bhadravathi new bridge. Two number of sewage drains dispose city sewage water in to the river directly.

Data Preparation

The data sets of 4 water quality monitoring stations which comprised of 10 water quality parameters monitored monthly over 2 years (2013-2014) are used for this study. The data is obtained from the water Quality Monitoring work of Tunga River Basin in Shimoga District,

Karnataka State Although there are more water quality parameters in these stations, only 10 most important parameters are chosen because of their continuity in measurement through the 12 years. The 10 selected water quality parameters include Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Chlorides (Cl), Total Dissolved Solids (TDS), Conductivity, Temperature and pH.

Analysis of samples

The water samples were collected from each of the five selected stat ions according to the standard sampling methods (IS: 2488, 1966 APHA, 1998).Samples for estimating dissolved oxygen (DO) and biochemical oxy gen demand (BOD) were collected separately in BOD(glass) bottles. Water temperature was recorded on the spot using thermometers.

RESULT AND DISCUSSION

Temperature was found to be ranged between 14 0C (minimum) to 280C (maximum) with average value of 210+9.90C from all the sites. Impinging solar radiation and the atmospheric temperature brings interesting spatial and temporal changes in natural waters. The rise in temperature of water accelerates chemical reactions, reduces solubility of gases, amplifies taste and odour and elevates metabolic activity of organisms (Usharani et al., 2010).

pH of the aquatic system is an important indicator of the water quality and the extent pollution in the watershed areas. pH was recorded to be varying from 6.43 (minimum) to 9.13 (maximum) with an average value of 7.78+1.91 from all the sites (Jonnalagadda et al.,2001). It has been mentioned that the increasing pH appear to be associated with increasing use of alkaline detergents in residential areas and alkaline material from wastewater in industrial areas (Chang, H., 2008)

Conductivity is a good and rapid method to measure the total dissolved ions and is directly related to total solids. Higher the value of dissolved solids, greater the amount of ions in water (Bhatt.,1999). The range of Electrical conductivity from all the sites was recorded as 340.00

Âµmhos (minimum) to 734.00 Âµmhos (maximum) with an average value of 537.00+278.60 Âµmhos

The value of Dissolved Oxygen is remarkable in determining the water quality criteria of an aquatic system. In the system where the rates of respiration and organic decomposition are high, the DO values usually remain lower than those of the system, where the rate of photosynthesis is high (Mishra et al., 2009). During the study period DO was found to be ranging between 4.90 mg/l (minimum) to 8.50 mg/l (maximum) from all the sites with an average value of 6.70+2.55 mg/l.

Biochemical Oxygen Demand is a measure of the oxygen in the water that is required by the aerobic organisms. The biodegradation of organic materials exerts oxygen tension in the water and increases the biochemical oxygen demand (Abida, 2008).BOD has been a fair measure of cleanliness

of any water on the basis that values less than 1-2 mg/l are considered clean, 3 mg/l fairly clean, 5 mg/l doubtful and 10 mg/l definitely. During the study period BOD varied from 3.00 mg/l (minimum) to 8.00 mg/l (maximum) with an average value of 5.50+3.54 mg/l at all the sites.

Chemical Oxygen Deand is a measure of the oxidation of reduced chemicals in water. It is commonly used to indirectly measure the amount of organic compounds in water. The measure of COD determines the quantities of organic matter

found in water. This makes COD useful as an indicator of organic pollution in surface water (King et al., 2003).COD pointing to a deterioration of the water quality likely caused by the discharge of municipal waste water (Mamais et al., 1993). In the present study COD was found to be ranging from 11 mg/l (minimum) to 24 mg/l (maximum) with average value of 17.50+9.19 at all the sites.

Alkalinity of water is a measure of weak acid present. Total alkalinity of water is due to presence of mineral salt present in it. Alkalinity was ranged between 123.00 mg/l (minimum) to 240.00 (maximum) mg/l with average value of 181.50+82.73 mg/l from all the sites.

Total hardness is the parameter of water quality used to describe the effect of dissolved minerals (mostly Ca and Mg), determining suitability of water for domestic, industrial and drinking purpose attributed to presence of bicarbonates, sulphates, chloride and nitrates of calcium and magnesium (Taylor, 1949). The variation in Total hardness during study period at all the sites was recorded as

mg/l to 475.00 mg/l with average value of 352.50+173.24 mg/l

Chlorides occur naturally in all types of water. High concentration of chloride is considered to be the indicators of pollution due to organic wastes of animal or industrial origin. Chlorides are troublesome in irrigation water and also harmful to aquatic life (Rajkumar, 2004). The levels of chloride in the present study were ranging from 18.00 mg/l (minimum) to 32.00 mg/l (maximum) with an average value of 25.00Â±9.90 mg/l at all the sites.

Fluoride concentration is an important aspect of hydrogeochmistry, because of its impact on human health. The recommended concentration of Fluoride in drinking water is 1.50 mg/l. The values recorded in this study was ranged between 0.40 mg/l (minimum) to 1.20 (maximum) mg/l with an average value of 0.80Â±0.57 mg/l from all the sites.

Table 1: Physico-chemical qualities of river water

Where D.O.= Dissolved Oxygen, BOD= Biochemical Oxygen Demand, COD= Chemical Oxygen Demand, TH= Total Hardness.

The present study concluded that river water of study area was moderately polluted in respect to analyzed parameters. pH, total hardness, chloride and fluoride were found within permissible limit but the higher values of BOD and COD in present study attributed river water was not fit for drinking purpose. It needs to aware local villagers to safeguard the precious river and its surrounding

APHA. Standard methods for the examination of water and wastewater.18thEdition, Washingoton, D.C 1992

Abida, B. and Harikrishna Study on the Quality of Water in Some Streams of Cauvery River, E- Journal of Chemistry, 5, (2): 377-384. 2008.

Eletta O. A.A Llnd Adekola F.A.. Studies Of The Physical and

Chemical Properties Of Asa River Water, Kwara State, Nigeria. Science Focus Vol, 10 (l), 2005 pp 72 76.

Jonnalagadda, S.B., and Mhere,G. Water quality of the odzi river in the eastern highlands of zimbabwe.Water Research, 35(10): 2371- 2376. 2001

Meitei, N.S., Bhargava and Patil, P.M. Water quality of Purna river in Purna Town, Maharashtra state. J. Aqua. Biol., 19- 77, 2005

Manjappa,S.,Suresh,B., Arvinda, H.B., Puttaiah, E.T., Thirumala,S. Studies on environmental status of Tungabhadra river near Harihar, Karnataka (India),J. Aquqa. Biol, vol 23(2): 67-72,2004

Mishra, A., Mukherjee, A. and Tripathi, B.D. Seasonal and Temporal Variation in Physico- Chemical and Bacteriological Characteristics of River Ganga in Varansi. Int. J.Environ. Res., 3(3): 395-402.2009

Rajkumar, S., Velmurugan, P., Shanthi, K., Ayyasamy, P.M. and Lakshmanaperumalasamy, P.(2004). Water Quality of Kodaikanal lake, Tamilnadu in Relation to PhysicoChemical and Bacteriological Characteristics, Capital Publishing Company, Lake 2004, pp.339- 346

Trivedi, R.K. and Goel, P.K. Chemical and biological methods

for water pollution studies. Environ. Publication, Karad. Maharashtra, India ,1994.

Usharani, K., Umarani,K., Ayyasamy, P.M., Shanthi, K.Physico- Chemical and Bacteriological Characteristics of Noyyal River and Ground Water Quality of Perur, India. J. Appl. Sci. Environ. Manage. Vol.14(2) 29-35,2009

ACKNOWLEDGEMENT

I would like to thank principal of RajaRajeswari College of Engineering and Management of RajaRajeswari Group of Institutions for extending encouragement and support to present the paper in the International Conference at T.John College of Engineering, Bangaluru

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For the Instructor

Mississippi River Case Study

Dead Zone in the Gulf of Mexico

Agricultural runoff can contribute pollutants to natural waters, such as rivers, lakes, and the ocean, that can have serious ecological and economic impacts, such as the creation of areas with low levels of dissolved oxygen called dead zones caused by pollution from fertilizers. Nutrients , such as nitrogen and phosphorus, are elements that are essential for plant growth and are applied on farmland as fertilizers to increase the productivity of agricultural crops. The runoff of nutrients (nitrogen and phosphorus) from fertilizers and manure applied to farmland contributes to the development of hypoxic zones or dead zones in the receiving waters through the process of eutrophication (Figure 4.2.7).

Watch the following videos from NOAA's National Ocean Service that show how dead zones are formed and explain the dead zone in the Gulf of Mexico:

Video: Happening Now: Dead Zones in the Gulf 2017 (2:33)
Video: Hypoxia (3:51)

The nutrients that make our crops grow better also fertilize phytoplankton in lakes and the ocean. Phytoplankton are microscopic organisms that photosynthesize just like our food crops. With more nitrogen and phosphorus available to them, they grow and multiply. When the phytoplankton dies, decomposers eat them. The decomposers also grow and multiply. As they're eating all of the abundant phytoplankton, they use up the available oxygen in the water. The lack of oxygen forces mobile organisms to leave the area and kills the organisms that can't leave and need oxygen. The zone of low oxygen levels is called a hypoxic or dead zone. Streams flowing through watersheds where agriculture is the primary land use exhibit the highest concentrations of nitrogen (Figure 4.2.8).

graph of Nitrogen concentrations in streams draining watersheds with different land uses

The Mississippi River is the largest river basin in North America (Figure 4.2.9), the third largest in the world, and drains more than 40 percent of the land area of the conterminous U.S., 58 percent of which is very productive farmland (Goolsby and Battaglin, 2000). Nutrient concentrations in the lower Mississippi River have increased markedly since the 1950s along with increased use of nitrogen and phosphorus fertilizers (Figure 4.2.10). When the Mississippi River's nutrient-laden water reaches the Gulf of Mexico, it fertilizes the marine phytoplankton. These microscopic photosynthesizing organisms reproduce and grow vigorously. When the phytoplankton die, they decompose. The organisms that eat the dead phytoplankton use up much of the oxygen in the Gulf's water resulting in hypoxic conditions. The resulting region of low oxygen content is referred to as a dead zone or hypoxic zone. The dead zone in the Gulf of Mexico at the mouth of the Mississippi River has grown dramatically and in some years encompasses an area the size of the state of Connecticut (~5,500 square miles) or larger. Hypoxic waters can cause stress and even cause the death of marine organisms, which in turn can affect commercial fishery harvests and the health of ecosystems.

Map of Mississippi and Atchafalaya River Basin and hypoxic zone in Gulf of Mexico

Figure 4.2.9. The Mississippi and Atchafalaya River Basin and the hypoxic zone in the Gulf of Mexico

Credit: USGS Factbook - Nitrogen in the Mississippi Basin-Estimating Sources and Predicting Flux to the Gulf of Mexico

graph of Nitrogen inputs and population from 1940-2010

Optional Reading

Additional resources about the dead zone in the gulf of mexico.

NOAA sponsored program out of LSU runs the hypoxia net website with great information ( Hypoxia Research Program')
Hypoxia and Eutrophication from the National Centers for Coastal Ocean Science of the NOAA Nation Ocean Service
USGS Fact Sheet 105-03, 2003, Nutrients in the Upper Mississippi River: Scientific Information to Support Management Decisions

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Experts share remarkable effects of removing restrictive dams from river: 'A case study in how we can improve habitat'

A multimillion dam removal project in Colorado is already having a positive impact on a river, and experts believe further investigation will provide valuable insights into restoring ecosystems.

The Denver Gazette reported that rainbow trout and brown trout are now easily able to swim to their spawning grounds after crews finished breaking down the concrete Colorado Springs Utilities diversion dam in 2023.

Around $4.8 million was invested in the project, which connected 45 miles of river and aimed to prevent the possibility of dam failure . Prior to the deconstruction of the dam, the trout were unable to get where they needed to go.

"We're watching fish every day try to jump over that dam and just bounce right off," FlyWater construction manager Nick Saylor told the Gazette in October 2023.

According to the World Wildlife Fund , dam removals can go a long way toward restoring the health of our rivers and aiding biodiversity. Since 1970, freshwater species populations have dropped by 83% on average. That, in turn, impacts humans who rely on those species for food, recreation, and income.

River restoration also makes the surrounding areas more resilient amid the uptick in severe weather events supercharged by a changing climate .

Watch now: Delta chief sustainability officer reveals how company plans to appeal to conscious consumers

Fortunately, nonprofit American Rivers reported that the United States deconstructed 80 dams in 2023. Projects in Maine , California , and Oregon are among the initiatives that have already resulted in remarkable ecosystem recoveries.

Now, according to the Gazette , scientists are monitoring a streambed of Eleven Mile Canyon. Since dams don't typically get removed in steep mountain canyons, the data is unique.

"The idea is that we can take what we gained from this study, to make it easier to predict how other places will respond if we remove dams like this in the future," Forest Service Rocky Mountain Research Station research geomorphologist Charlie Shobe told the news outlet.

Researchers are also investigating the impact of dams along the South Platte River, at Eleven Mile, and the Cheesman Reservoir, which are remaining to help the region meet its water demands.

"It's kind of a case study in how we can improve habitat over large reaches of a river and improve the functioning of the river channel while still meeting user water needs," Shobe added .

Restoration efforts are ongoing, with crews revegetating the area with willows and grasses expected to support migratory birds . A new wheelchair-accessible trail is also being created so that more locals can get out and explore nature. The area is expected to reopen to the public in 2025.

Join our free newsletter for cool news and cool tips that make it easy to help yourself while helping the planet.

Experts share remarkable effects of removing restrictive dams from river: 'A case study in how we can improve habitat' first appeared on The Cool Down .

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Understanding rivers and their social relations: A critical step to advance environmental water management

Elizabeth p. anderson.

1 Department of Earth and Environment and Institute for Water and Environment, Florida International University, Miami, Florida, USA

Sue Jackson

2 Australian Rivers Institute, Griffith University, Nathan, Queensland, Australia

Rebecca E. Tharme

3 Riverfutures Ltd, Buxton, UK

Michael Douglas

4 University of Western Australia, Perth, Western Australia, Australia

5 Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, Australia

Joseph E. Flotemersch

6 U.S. Environmental Protection Agency, Office of Research and Development, Cincinnati, Ohio, USA

Margreet Zwarteveen

7 IHE-Delft Institute for Water Education, Delft, the Netherlands

8 Amsterdam Institute for Social Science Research, University of Amsterdam, Amsterdam, the Netherlands

Chicu Lokgariwar

9 Peoples’ Science Institute, Dehradun, Uttarakhand, India

Mariana Montoya

10 Wildlife Conservation Society, Lima, Peru

11 Integrated Research Center, The Field Museum, Chicago, Illinois, USA

Gail T. Tipa

12 (Ngai Tahu) Tipa and Associates Ltd, East Taieri, New Zealand

Timothy D. Jardine

13 School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

Julian D. Olden

14 School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington, USA

15 Water Practice, Worldwide Fund for Nature (WWF-China), Beijing, China

John Conallin

16 Institute of Land, Water and Society, Charles Sturt University, Albury, New South Wales, Australia

Barbara Cosens

17 University of Idaho College of Law, Moscow, Idaho, USA

Chris Dickens

18 International Water Management Institute, Pretoria, South Africa

Dustin Garrick

19 School of Enterprise and the Environment, University of Oxford, Oxford, UK

David Groenfeldt

20 Water-Culture Institute, Santa Fe, New Mexico, USA

Jane Kabogo

21 Ministry of Water and Irrigation, United Republic of Tanzania, Dodoma, Tanzania

Dirk J. Roux

22 Scientific Services, South African National Parks, George, South Africa

23 Sustainability Research Unit, Nelson Mandela University, George, South Africa

Albert Ruhi

24 Department of Environmental Science, Policy, and Management, University of California, Berkeley, California, USA

Angela H. Arthington

25 Australian Rivers Institute, Griffith University, Nathan, Queensland, Australia

River flows connect people, places, and other forms of life, inspiring and sustaining diverse cultural beliefs, values, and ways of life. The concept of environmental flows provides a framework for improving understanding of relationships between river flows and people, and for supporting those that are mutually beneficial. Nevertheless, most approaches to determining environmental flows remain grounded in the biophysical sciences. The newly revised Brisbane Declaration and Global Action Agenda on Environmental Flows (2018) represents a new phase in environmental flow science and an opportunity to better consider the co-constitution of river flows, ecosystems, and society, and to more explicitly incorporate these relationships into river management. We synthesize understanding of relationships between people and rivers as conceived under the renewed definition of environmental flows. We present case studies from Honduras, India, Canada, New Zealand, and Australia that illustrate multidisciplinary, collaborative efforts where recognizing and meeting diverse flow needs of human populations was central to establishing environmental flow recommendations. We also review a small body of literature to highlight examples of the diversity and interdependencies of human-flow relationships—such as the linkages between river flow and human well-being, spiritual needs, cultural identity, and sense of place—that are typically overlooked when environmental flows are assessed and negotiated. Finally, we call for scientists and water managers to recognize the diversity of ways of knowing, relating to, and utilizing rivers, and to place this recognition at the center of future environmental flow assessments.

This article is categorized under:

Water and Life > Conservation, Management, and Awareness

Human Water > Water Governance

Human Water > Water as Imagined and Represented

1 |. INTRODUCTION

Freshwater is arguably the most critical substance for life on Earth: it is essential for ecosystem health and underpins the economies and lifeways of human populations around the world ( UN Environment, 2017 ; WWAP, 2018 ). For generations, water resource management as conceived and practiced in more industrialized regions of the world has construed freshwater as a natural, asocial substance that can be objectively known and—in efforts to maximize its potential as a resource—controlled and regulated for human welfare. Thus “knowing, accounting for and representing water apart from its social context” is part of a particular modern hydrological knowledge paradigm that, by the end of the twentieth century, had come to dominate the myriad ways to know and relate to freshwater ( Linton, 2014 , p. 111; Wantzen et al., 2016 ; Magdaleno, 2018 ).

For numerous reasons, the modern conception of water as a substance abstracted from social, cultural, and religious context has come under heightened scrutiny. Consequently, there has been greater interest in addressing how water is not just natural, but also historical, political, and cultural. This interest has generated attention to approaches other than eco-hydrological methods to know and understand water and has led to increased recognition of the complexity of the relations between water, society, and ecosystem processes. This is, for instance, manifest in recent scholarship on socio-hydrology ( Sivapalan, Savenije, & Blöschl, 2012 ) and the hydro-social cycle ( Bakker, 2012 ; Boelens, 2014 ; Linton & Budds, 2014 ), both bodies of work in which natural and social researchers collaborate because they acknowledge the need to understand water flows and systems as both social and natural ( Wesselink, Kooy, & Warner, 2017 ). Although the viewpoints emerging from socio-hydrology and the hydro-social cycle are founded on different knowledge paradigms, they are rooted in the core idea that water systems—like rivers—and society coevolve and emerge through continued engagement over space and time ( Wantzen et al., 2016 ). Ethnographic studies of customary hydraulic systems and their communal water management institutions have also contributed to such an understanding. These include the subak irrigation system (cooperatives) of Bali ( Lansing, 2006 ) and the self-sufficient acequia systems that have persisted for several hundred years in the southwestern United States ( Cox, 2014 ). The increased scholarly acknowledgement of the mutual constitution of society and water has also been translated into policies and international frameworks that seek to address complex, interdependent societal challenges, for example, the Sustainable Development Goals (SDGs). A specific goal for water—SDG6: Ensure availability and sustainable management of water and sanitation for all —along with other SDGs focused on peace, justice, climate, conservation, and well-being, seek to explicitly link water and social relations ( Wiegleb & Bruns, 2018 ).

Those interested in environmental flows also increasingly recognize the importance and complexity of relationships between humans and freshwater bodies. According to the renewed Brisbane Declaration of 2018, the term environmental flows refers to: the quantity, timing, and quality of freshwater flows and levels necessary to sustain aquatic ecosystems which, in turn, support human cultures, economies, sustainable livelihoods, and well-being ( Arthington et al., 2018 ; Box 1 ). Environmental flow assessment—also sometimes referred to as environmental water allocation or environmental water management—is a critical step in establishing a societally-acceptable threshold between water available for off-channel allocations and water to be retained within or returned to a waterbody to sustain ecosystems. The science of environmental flows embraces the full range of aquatic ecosystems, however the focus of this paper is on rivers and their social relations.

THE BRISBANE DECLARATION AND GLOBAL ACTION AGENDA ON ENVIRONMENTAL FLOWS (2018)

In 2018, scientists, river conservationists, and water managers revisited the Brisbane Declaration and Global Action Agenda of 2007. In the decade between the first and second declarations, the environmental flow community had come to appreciate that “social and cultural dimensions of environmental flow management warrant far more attention” ( Arthington et al., 2018 , p. 2). Thus, a significant new element of the 2018 Declaration and Global Action Agenda is the emphasis given to “full and equal participation for people of all cultures, and respect for their rights, responsibilities and systems of governance in environmental water decisions” ( Arthington et al., 2018 , p. 12).

The Declaration sets out six statements, all pertinent in the context of this paper:

Environmental flows are essential to protect and restore biodiversity, aquatic ecosystems, and the ecosystem services they provide for all societies.
Environmental flows are critical to protect and safeguard the world’s cultural and natural heritage.
Environmental flows have been compromised and today many aquatic systems around the world are at risk.
Implementation of environmental flows requires a complementary suite of policy, legislative, regulatory, financial, scientific, and cultural measures to ensure effective delivery and beneficial outcomes.
Local knowledge and customary water management practices can strengthen environmental flow planning, implementation, and sustainable outcomes.
Climate change increases the risk of aquatic ecosystem degradation and intensifies the urgency for action to implement environmental flows.

The Action Agenda contains over 30 recommendations to support and advance environmental flow implementation organized under the categories: leadership, management, and research. A central recommendation is to “develop and implement a legal basis for regulating water use, environmental flows, water rights, and licenses, including recognition of cultural heritage values, knowledge, and customary relationships with water” ( Arthington et al., 2018 , p. 12).

The revised Declaration “heralds a new era of scientific innovation, shared visions, collaborative implementation programs and adaptive governance of environmental flows, with ample opportunities for engagement across multiple sectors, disciplines, regions, and cultures” ( Arthington et al., 2018 , p. 7).

Despite the inclusion of a hydro-social perspective in the new definition and advances in several assessment frameworks ( Poff, Tharme, & Arthington, 2017 ), the science and practice of environmental flows has so far remained faithful to distinctly modern methodologic traditions. These traditions have their origins in the biophysical sciences and are mostly premised on a separation between nature and society. With some exceptions ( Acreman et al., 2014 ; King, Tharme, & Villiers, 2000 ; Poff et al., 2010 ), the overwhelming majority of approaches used for determining environmental flows remain based predominantly on (a) hydrology; (b) physical habitat simulation for fish or other aquatic biota; or (c) flow-ecology relationships where people are excluded from important ecological relations or concepts, like aquatic food webs ( Tharme, 2003 ). Few studies have considered the role of river flow in the livelihoods and well-being of local communities and highlighted vital social and economic dependencies. Consequently, the embedded, reciprocal, and constitutive relationships that many human populations have with water and rivers continue to be poorly understood.

We argue that a challenge for environmental flows research and implementation is to understand natural systems in relation to the social world, in line with what those who seek to advance hydro-social thinking are trying to do ( Wesselink et al., 2017 ), and to appreciate rivers and their flow regimes as social-ecological systems ( McGinnis & Ostrom, 2014 ). We posit that rivers are socially constituted in at least three ways. First, historical, social, and political processes and contexts shape ways of knowing (e.g., conceptualizing and making abstractions about water and eco-hydrological processes) and acting on the environment, or in this case, rivers and waterways. As we will describe, the growing commitment to environmental flows and the expansion of methodological approaches grew from a shared political concern from environmentalists and scientists about the future of rivers and river-dependent ecosystems and societies. They were particularly concerned about those waterways directly affected by the modernist mode of water management, one that transformed rivers through regulatory infrastructures or other river alteration measures. Second, implementation of the prescriptions promoted by environmental flows scientists and advocates requires effective frameworks, technologies and institutions (norms, rules, laws), as well as widespread political-social support and alignment with the aspirations of those people responsible for and living with rivers subject to alteration. Third, the implementation of environmental flows will have social and political consequences that result from decisions to redistribute water or share it differently, by “taking away” water from some and allocating it to others or allowing it to remain in the environment. Similar to environmental flows, the importance and influence of societal values, priorities, and perceptions of nature also are increasingly recognized as inherent to river restoration ( Lave, 2016 ; Smith, Clifford, & Mant, 2014 ).

This paper is the first to synthesize knowledge of relationships between people and rivers as conceived under the renewed definition of environmental flows (see Box 1 ). We trace the historical underpinnings of environmental flows and explore how social norms and values have influenced scientific understandings of rivers, a neglected aspect of the historiography of river science. We then review a specific but small body of literature that describes multidisciplinary efforts in which satisfying diverse flow needs for human livelihoods or well-being has been central to setting environmental flow recommendations. Several of these efforts were undertaken with the realization that implementing environmental flows requires active support of stakeholders, as well as their knowledge, spiritual beliefs, and the symbolic meanings they attribute to rivers. We conclude with a discussion of the diversity of flow-human relationships that typically remain overlooked when environmental flows are assessed and negotiated ( Table 1 ), and a call for greater recognition of these relationships.

Select examples of cases and references illustrating various interlinked relationships between humans and rivers from different regions and cultures of the world

The ideas presented here emerged from discussions among ~25 people at a week-long workshop on social and eco-hydrological linkages to environmental flows, convened in June 2017 at the Socio-Ecological Synthesis Center (SESYNC) in Annapolis, Maryland, USA. Workshop participants intentionally represented diverse backgrounds (e.g., government, non-government, Indigenous) and nationalities, and collectively brought together decades of experience in theory, research methods, assessment, negotiation, and implementation of environmental flows, and/or knowledge of the varied connections human societies maintain with rivers.

2 |. HOW HAS ENVIRONMENTAL FLOW SCIENCE HISTORICALLY CONCEIVED OF RIVER-HUMAN INTERACTIONS?

There is some evidence that state water management practices considered some aspects of societies’ relations with rivers and the social significance of flowing water, even before environmental flows took shape as a scientific field and river conservation practice in the late 20th century. Yet, this consideration was often partial, with river relationships maintained by certain marginalized groups, such as Indigenous peoples in setter societies, afforded little regard or protection by modernist (and in many cases, colonial) approaches to water management (see Emanuel, 2019 ; Estes, 2017 ; Robison, Cosens, Jacskon, Leonard, & McCool, 2018 ). In 1915, in a move to recognize the aesthetic value of a river, Oregon (USA) prohibited the diversion of water from certain streams that sustained the spectacular falls of the Columbia River Gorge ( Lamb & Doerksen, 1987 ). A 1917 agreement from India shows that the British colonial government recognized the importance of flows for religious purposes on the Ganges River and duly amended plans for water infrastructure following interjections from local rulers (General Administration Department, No. 10, April 28, 1917). In the 1960s–1970s, scientists in southern Africa investigated the intricate relationships between the livelihoods of the Thonga people and floodplain dynamics along the Pongola River ( Heeg & Breen, 1982 ; Tinley, 1964 ). Their studies informed recommendations for managed flow releases from an upstream impoundment to meet fishery and other tribal needs downstream, although that advice was not incorporated into operating rules at the time. Such frontrunners to the concept of environmental flows are not well recognized in the international scientific literature.

In the documented histories of river conservation (e.g., Poff & Matthews, 2013 ), it was the era of extensive dam building that promulgated the concept and practice of environmental flows. In the mid-20th century, and particularly in the United States, development of water supplies by the agencies of the state using large-scale infrastructure was the prevailing response to the problems of “modern” water management ( Linton, 2014 ). The first generalized set of environmental flow recommendations is commonly attributed to Donald Tennant, a biologist who, while working for the U.S. Fish and Wildlife Service during the 1950s–1960s, made hundreds of observations about flow-altered and unaltered rivers in Montana, Wyoming, and Nebraska. Based on these observations, Tennant devised the Montana Method for calculating minimum, moderate, and excellent flow levels to protect aquatic resources downstream from dams based on varying percentages of average annual or seasonal flow ( Tennant, 1976 ). By 1969, Montana had become the first U.S. state to provide for the legal acquisition of a water right for in-stream uses, a move that also allowed its fish and game department to acquire such rights ( Lamb & Doerksen, 1987 ). Other U.S. states followed suit, stimulating the need for scientifically legitimate methods of assessing flows. Although the Montana Method is often described as hydrology-based method, a lesser-known fact is that the underpinning research also included studies of “fishing and floating” and “esthetics and natural beauty” as outcomes linked to river flows, and documented water velocities suitable for white-water boating.

The 1970s–1980s witnessed a shift from equating environmental flows with hydrology-based minimums to greater recognition of relationships between flow and hydraulic conditions linked to physical habitat for aquatic organisms and to recreational uses of water ( Stalnaker, Lamb, Henriksen, Bovee, & Bartholew, 1995 ; Tharme, 2003 ). Additionally, in the United States, a growing multiple-use ethic of water led to the consideration of water budgets for different uses, such as instream fisheries, and understanding that these budgets vary across the year. During this period, the Instream Flow Incremental Methodology (IFIM), developed by the U.S. Fish and Wildlife Service, U.S. Geological Survey, and other partners, created an analytical framework to evaluate various alternatives for use of instream flows within a hydrologic time series. IFIM is often confounded with the Physical Habitat Simulation System (PHABSIM), a tool that links open channel hydraulics with aquatic biota and calculates habitat available for different fish life stages at varying flow levels ( Bovee & Milhous, 1978 ). However, PHABSIM forms only one component of IFIM. The overall structure of IFIM heralded recognition of the value of an interdisciplinary approach to instream uses, including not only water management and hydrology, but also political science and law. It offered a platform to recognize all users of water in decision-making about environmental flows, including recreational and Indigenous tribal uses ( Stalnaker et al., 1995 ). The more integrated framing of IFIM is not as frequently used, nor as well known as the quantitative aspects of PHABSIM, but in reality, it represented an early awareness of diverse human connections to the flow characteristics of rivers.

Appreciation for recreational uses and their linkages to river flow gained additional strength in the 1970s–1980s. Brown, Taylor, and Shelby (1991) reviewed ~25 river-specific studies of recreational quality, economic value, and esthetics, and their interactions with other needs for river flows. They distinguished between direct effects of river flows on recreational attributes of rivers—such as quality of flows for boating, fishing, and scenic beauty—and indirect or longer-term effects related more to the form and function of river channels and riparian habitats. These studies consistently identified a range of responses to putative minimum, optimum, and maximum flow conditions, thereby highlighting the importance of considering variation in perceptions among recreationalists ( Brown et al., 1991 ). Around the same time (1980s–1990s), in response to adjudication of water rights in the western U.S., the U.S. Forest Service developed an approach to identify channel maintenance flows to reflect the original intention of national forest protection defined in the Organic Administration Act of 1897 ( Schmidt & Potyondy, 2004 ). Flows that would maintain stream channels over time could also ensure the delivery of water to downstream users.

The development and application of more comprehensive approaches to determining environmental flows—often referred to as “holistic” approaches (sensu Tharme, 2003 )—represented a further development in systematically recognizing the connections between people and rivers ( Poff & Matthews, 2013 ). From the late 1980s, as scientists grew more aware of the inherent variability in a river’s hydrologic regime and the importance of this variability to multiple aspects of a river’s ecology ( Poff et al., 1997 ; Richter, Baumgartner, Wigington, & Braun, 1997 ), they were increasingly preoccupied with the conservation and management challenges posed by widespread river alteration, particularly by hydropower dams ( Cushman, 1985 ; Dynesius & Nilsson, 1994 ; Ligon, Dietrich, & Trush, 1995 ). This era (mid-1990s to early 2000s) saw the development and application of two new methodologies that incorporated societal goals for the future ecological condition of a river when setting flow objectives. The first of these was the Building Block Methodology (BBM) developed in South Africa ( King et al., 2000 ). A second methodology, known as Downstream Response to Imposed Flow Transformations (DRIFT), explicitly considered the “sociological” consequences of flow-related biophysical changes, giving them equal weight to other impacts encompassed by a “biophysical module” ( King & Brown, 2006 ). Using DRIFT, flow alterations affecting fisheries ( Arthington, Rall, Kennard, & Pusey, 2003 ), riparian vegetation, and water quality ( King, Brown, & Sabet, 2003 ) were considered by teams that comprised specialists involved in the fields of ecology, livestock health, public health, anthropology, sociology, water use, and resource economics ( King & Brown, 2006 ).

This period marked an advance in environmental flows through a broadened perspective to an ecosystem level, greater involvement from various stakeholders in establishing goals for river flow management, and recognition of socio-economic dependencies on flows and consequences of altered flows for human communities. Nevertheless, several limitations remained. Most environmental flow approaches of this time saw the natural world as separate from and external to the social world and sought to reconstruct an “original nature” against which human environmental practices such as flow alteration could be judged ( Richter et al., 1997 ). As a consequence of this framing and because of a biocentric approach to the research task, the focus in most methodologies remained on ecologically significant variables and processes, and their linkages to flow. Social considerations were limited to descriptions of how altered flows could affect vulnerable people; measured impacts typically related to subsistence reliance on fish and other aquatic resources, rather than being used as metrics to help set environmental flow recommendations around underlying human interactions with rivers. Furthermore, most progress on approaches described as “holistic” was still limited to a small number of regions, primarily South Africa and Australia ( Arthington, 2012 ; Poff & Matthews, 2013 ; Tharme, 2003 ).

By the turn of this century, the development and application of environmental flows had spread worldwide, with various motivating factors ( Poff et al., 2017 ). For example, in the African nations of Kenya and Tanzania, numerous flow assessments were conducted in response to new water policy frameworks that gave second priority to ecosystems in water allocation decisions, following satisfaction of basic human needs for water ( Dickens, 2011 ; Kabogo, Anderson, Hyera, & Kajanja, 2017 ; McClain, Kashaigili, & Ndomba, 2013 ). A proliferation of new hydropower projects precipitated environmental flow assessments in other places—such as Central and South America ( Anderson et al., 2018 ; Anderson, Pringle, & Rojas, 2006 ; Esselman & Opperman, 2010 ), southeast Asia including China ( Illaszewicz, Tharme, Smakhtin, & Dore, 2005 ; Wang et al. 2009 ; Blake et al., 2011 ) and Central Asia ( USAID, 2017 ). While these approaches maintained a heavy focus on hydrology or habitat-based methodologies, they included a social assessment component in some cases (e.g., Poff et al., 2017 ). Here, as with the cases referred to above, these assessments relied primarily on ecological variables to understand and quantify the relationships between people, flows and desirable ecosystem properties, often with a strong focus on economic consequences for riparian communities.

From the mid-2000s to the present, globalization has increasingly transformed and unified the science and practice of environmental flows. The first Brisbane Declaration (2007) established a common definition and global action agenda to advance environmental flows science and management. It also consolidated an international community of environmental flows practitioners that included scientists, water agencies, environmental NGOs, and engineers—those who had historically been involved—with newcomers to environmental flows from the financial, government, humanitarian, and development assistance sectors ( Poff & Matthews, 2013 ). Together, this community has expanded environmental flows science and practice far beyond its historical foundations. Today, numerous countries in Central and South America, Africa, and Asia have established legislation and advanced practical experience related to environmental flows ( Anderson et al., 2011 ; McClain & Anderson, 2015 ; Poff et al., 2017 ; Harwood et al. 2018 ).

The international community also moved to synthesize and scale up scientific knowledge of ecological responses to flow alteration ( Arthington, Bunn, Poff, & Naiman, 2006 ). The regional Ecological Limits of Hydrologic Alteration (ELOHA) framework emerged, and with it a river basin approach that articulates and quantifies testable hypotheses of ecological responses to altered flows to guide environmental flow determination ( Poff et al., 2010 ). The ELOHA incorporates human dimensions into environmental flow setting through explicit consideration of societal preferences for flow conditions and through its commitment to adaptive management ( Poff et al., 2010 ). Nevertheless, similar to earlier methodologies seeking to incorporate societal or human dimensions and variables, the core of ELOHA’s framework focuses on flow alteration-ecological response relationships. Among ELOHA’s limitations is that it has yet to consider the profound and complex interactions between people, river flows, and the governance of water, or to give critical attention to the relationships between science and society. ELOHA also privileged eco-hydrological science in the making of flow recommendations (see Finn & Jackson, 2011 ; Pahl-Wostl et al., 2013 ).

In an effort to incorporate matters of governance and strengthen the capacity for comparisons between different rivers, some researchers set out to improve the consideration ELOHA had given to the social sciences in a new framework referred to as Sustainable Management of Hydrological Alterations (SUMHA) ( Pahl-Wostl et al., 2013 ). The revised approach sought to achieve greater engagement in environmental flows research and traction within the water management sector by attending explicitly to the needs of stakeholders and including social sciences in assessment, sectoral tradeoff analysis, and other steps ( Pahl-Wostl et al., 2013 ). However, the framework could have benefited from deeper reflection on its foundational ontological and epistemological assumptions. As with previous methodologies, SUMHA and the underpinning ELOHA framework rely on an understanding of “nature” as external to social relations. More precisely, in these models, researchers conceive of water and ecosystems as resources that exist independently of social relations and can be objectively known and quantified by scientists. Furthermore, SUMHA adopts the framework of “ecosystem services” to bridge the social and eco-hydrological realms without questioning whether a universal approach to value articulation will assist the goal of understanding differences across the socio-ecological systems of the world’s rivers. Relational values are the key to pluralistic environmental valuation ( Himes & Muraca, 2018 ), and so the emphasis given by SUMHA to instrumental values is one of its limitations.

That SUMHA is premised on the ecosystem services framework is not surprising given that the globalization of environmental flows has been accompanied by growing and widespread recognition of the ecosystem services concept ( MEA, 2005 ). Freshwater ecosystem services are described as the numerous benefits humans derive from rivers and other aquatic systems in terms of provisioning goods like water, food, or fiber; regulating processes like flood control; supporting services like nutrient cycling or waste assimilation; and cultural appreciation of freshwater through spiritual and recreational benefits ( Bark et al., 2016 ).

Since the concept’s ascendance, freshwater ecosystem services have often been used in environmental flow assessments to describe a one-way flow of benefits from the human uses of rivers ( Forslund et al., 2009 ; Gilvear, Beevers, O’Keeffe, & Acreman, 2017 ; Gopal, 2016 ). Although the intention has been to raise awareness of human dependencies on rivers, in our view, the ecosystem services concept is inadequate in that it stresses nature’s provision of goods and services, but neglects the embedded, reciprocal and constitutive relationships that many human populations have with water and rivers ( Emanuel, 2019 ; Huertas & Chanchari, 2011 ; Jackson & Palmer, 2012 ; Tipa & Nelson, 2008 ). Rivers are not merely biophysical phenomena that constitute a component of an objectified and externalized nature that provides services to people. The relationship of the Lumbee people to the Lumbee river of North Carolina exemplifies the essential shortcoming of this economic concept. Informed by his experience as a Lumbee person and environmental scientist, Emanuel (2019) stresses the “bi-directional” or reciprocal relationship maintained by his tribe and its river. While acknowledging that the Lumbee River provides distinctive benefits, the relationship is not unidirectional:

“Lumbee people respect and honor the river, and they spend time in and around its waters for work, recreation, and worship. In doing so, the people and the river have each infused the other with identity to the extent that both share the same name (p. 5).”

As this quote reveals, rivers and their waters mediate social relationships through belief systems, cultural identity, institutions, knowledge and technology ( Figure 1 ). Flows connect people who relate to rivers through habitual practices and experiences that are influenced by ethics, morals and other means of socialization, and these relationships in turn shape flow regimes ( Emanuel, 2019 ; Wantzen et al., 2016 ). Human societies come to know the meaning of water and rivers from within social relationships ( Bakker, 2012 ; Krause & Strang, 2016 ). By emphasizing the relational character of human-river interactions, the concept and practice of environmental flows can provide a framework for improving our understanding of rivers as social-ecological systems.

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(a) The lives and livelihoods of people across the Amazon are inextricably linked to seasonal fluctuations in river flows. Rivers are also a key component of the culture of many Amazonian Indigenous groups, such as the Shawi (pictured here). (b) Rivers offer spaces, goods, and functions that mediate social interactions. Here, a gathering of canoes in the Peruvian Amazon. Photo credits: Alvaro del Campo, The Field Museum, USA

To date, this kind of relational thinking has gained the most traction in contexts where Indigenous peoples have a significant stake in a water management issue. This is readily apparent in the recent spate of cases that have afforded legal status of personhood to rivers ( Pecharroman, 2018 ). For example, several authors have recently described developments in Australia where the idea of “cultural flows” ( Johnston et al., 2012 ; Magdaleno, 2018 ; Weir, 2009 ) has taken hold as a complement to orthodox approaches to environmental flows ( Jackson, 2017 ). Similarly, Finn and Jackson (2011) urged researchers to consider Indigenous people’s attachments to rivers in environmental flow assessment, specifically Indigenous cosmologies and ethical responsibilities in water governance. The next phase of environmental flows science, heralded by the Brisbane Declaration and Global Action Agenda 2018 ( Box 1 )—and the renewed definition of environmental flows—represents an opportunity to further these developments, to embrace these alternative views of sustainability, and to better consider the co-constitution of river flows, ecosystems, and society. In the next section, we explore case studies that have advanced our understanding of diverse human relationships with rivers. These cases represent a bridge to an emerging mindset that seeks to recognize and foster mutually beneficial relationships of interdependence between people and rivers, as well as support the full participation of those with a stake in water management decisions.

3 |. CASE STUDIES: A DIVERSITY OF RELATIONSHIPS BETWEEN HUMANS AND RIVER FLOWS

There is a growing body of literature, mostly produced in the past decade, responding to the realization that the support of local people—those who most directly experience the effects of river alterations—is necessary if the goals of sustainable water management are to be met ( Conallin, Dickens, Hearne, & Allan, 2017 ; Kabogo et al., 2017 ; Lave, 2016 ). Attention within water governance to public participation and more generally to the importance of process coincided with changes in human rights law that have influenced international standards relating to community consent to water resource development. Two high profile international institutions have focused particular attention on the needs of Indigenous peoples who have suffered human rights violations and disproportionate negative impacts of large dams ( Carino & Colchester, 2010 ; Estes, 2017 ; Robison et al., 2018 ). Reporting in 2000, the World Commission on Dams helped establish as development best practice the requirement to respect the right of Indigenous peoples to give or withhold their “free, prior and informed consent” to development projects ( Carino & Colchester, 2010 ). Almost a decade later, the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP) affirmed the rights of Indigenous Peoples to “maintain and strengthen their distinctive spiritual relationship with their traditionally owned or otherwise occupied… waters” (Article 25 cited in Robison et al., 2018 , p. 856). The Declaration also imposed obligations on nation states to seek the free, prior and informed consent of Indigenous communities to water resource developments affecting them.

With this societal change in norms, it is becoming ever more important to satisfy the flow needs of riparian human populations dependent on rivers for their livelihood and well-being in setting environmental flow recommendations. This is a change from earlier considerations of human linkages to river flows, which focused heavily on recreational uses of rivers or scenic beauty (e.g., Brown et al., 1991 ). More recent studies have documented the linkages of river flows to floodplain agriculture, transportation, and social exchange, and to acts of reverence, cultural identity, or sense of place (see, e.g., Table 1 ; Figure 1 ).

In this section, we examine case studies from around the world that exemplify the more integrative conceptualization of environmental flows articulated in the Brisbane Declaration 2018. In that manifesto, environmental flows and aquatic ecosystems “ support human cultures, economies, sustainable livelihoods, and well-being ” ( Arthington et al., 2018 ; Box 1 ) and therefore need to build upon local ways of seeing and understanding rivers to protect not only well-established relationships, such as floodplain fisheries, but also the less visible and generally less easily quantifiable values of rivers in water resource allocation frameworks. Additionally, the selected cases offer a lens for a better understanding of power relations among stakeholders and the importance of trust in supporting and developing dynamic relationships between humans, river flow regimes, and aquatic ecosystems, through relationships that are sustainable, just, and inclusive.

3.1 |. The Patuca River, Honduras

The Patuca River, Honduras, is Central America’s third longest river and supports Indigenous Miskito and Tawahka who depend on it to sustain their lifeways. Additionally, the Patuca River is a primary conduit for transportation and communication in eastern Honduras, as much of its basin drains roadless areas. Since the 1970s, the national government has considered numerous hydropower projects. In 2006–2008, during planning for the Patuca III hydropower project, environmental flows were assessed under an agreement between The Nature Conservancy (TNC) and the Honduran National Electric Energy Corporation (ENEE) (see Esselman & Opperman, 2010 for a summary).

Scant published data on the ecology of the Patuca River were available to the environmental flows scientific team at the time of the assessment. Researchers sought to fill knowledge gaps by working with Indigenous Miskito and Tawahka. A diverse team of ecologists, hydrologists, and community members collected and systematized information for setting flow recommendations in workshops. Interviews with boat captains along the Patuca River linked low waters to extended travel time, increased risk of accidents, and associated costs. During workshops, Miskito and Tawahka community members annotated maps and photos to define river water levels important for key ecological components (e.g., fish, crocodile habitat), for vital social components (e.g., transportation, fishing), and for extreme events (e.g., Hurricane Mitch in 1998). External researchers relied on Indigenous knowledge of the river to form hypotheses about flow-dependent ecological characteristics of the Patuca River and to help them identify social factors that could be vulnerable to flow alterations ( Esselman & Opperman, 2010 ).

The process of establishing flow recommendations to ENEE for the operation of the Patuca III hydropower project focused on: (1) channel morphology; (2) aquatic organisms; and (3) terrestrial resources, human communities, and riparian forests. Researchers considered the reliance of Miskito and Tawahka communities on the Patuca River for transportation in flow recommendations, as well as the requirements for floodplain conditions to support agriculture and fisheries. Having identified the most challenging passage points for boat traffic, researchers estimated the flow levels above normal dry-season base flow level required to minimize barriers to river passage. The recommended flow rate was similar to the predicted mean outflow from the dam during normal dry-season operation.

The Patuca River case exemplifies incorporation of human dimensions in environmental flows in multiple ways. First, it involved a multidisciplinary team from diverse institutions and backgrounds, including numerous Indigenous people from the lower basin. Second, it relied primarily on local knowledge of Miskito and Tawahka peoples for understanding of flow-dependent ecological and social features of the Patuca River. Third, human dependencies on the flow dynamics of the Patuca River—for transportation, communication, floodplain agriculture, and fisheries—were incorporated as environmental flow recommendations.

3.2 |. The Ganga River, India

Millions of people consider India’s Ganga (Ganges) River sacred. Religious Hindu texts describe the river/goddess as: “ turbulent, sportive, moving, swift, leaping and booming ” and the River Ganga derives its name from the Sanskrit verb gam, meaning “to go” ( Eck, 1982 ). Over millennia, people throughout India have developed customs, rituals, and philosophies that reflect and align with the natural rhythms of the river. People depend on the Ganga for water for daily drinking and washing. Rituals such as ceremonial bathing and meditation, and traditional practices such as flood recession farming are critical to the maintenance of cultural identities. These uses of the Ganga were historically based on the availability of certain flows at different times of the year. ( Lokgariwar, Chopra, Smakhtin, Bharati, & O’Keeffe, 2014 ). People living beyond the basin also engage in some of these practices. For example, the Kumbh ceremony represents the world’s largest aggregation of people for a religious purpose. In 2013, over 80 million devotees visited Allahabad, India, to drink from and immerse themselves in the Ganga River to attain salvation ( WWF, 2013 ). The event’s significance was linked to high public expectations for adequate and clean flows in the Ganga during the celebration ( Sarkar, 2017 ).

Appreciating this context, environmental flow assessments undertaken by World Wildlife Fund (WWF) and partners for the Ganga River have focused on documenting and better quantifying socio-cultural relationships to flow, using the Building Block Methodology with inclusion of a component on cultural water requirements ( Lokgariwar et al., 2014 ; Figure 2 ). Review of historical and religious texts and participatory surveys and interviews with riverside human communities provided valuable information on the symbolic importance of the Ganga River locally and to the wider nation of India. Responses indicated that the built environment provided a means for record-keeping of historical flows, with temples and ghats (steps) marking levels of flow events. Interviewees frequently expressed cultural flow requirements with reference to depths at these sites and along banks, but also in terms of the width and depth of the Ganga channel. Using hydraulic cross-sections, the depths and widths required for cultural practices in different parts of the channel were converted into environmental flow requirements.

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Flow needs for religious and spiritual practices were central to an environmental flow assessment for the Ganga River, India. Here, a gathering of pilgrims for the Kumbh festival. Photo credit: Chicu Lokgariwar

To complete the environmental flow assessment, levels of water necessary for worship, ritual bathing, and cremation rites were estimated under three scenarios: (a) flows for maintenance years (neither too wet nor too dry); (b) flows for drought years; and (c) flood flows for both maintenance and drought years. This was followed by an assessment of flow needs for a successful Kumbh in 2013. Here too, a review of texts and interviews with elders, religious leaders and visitors to the key bathing sites collected data on the desired water depth, water surface width, and velocity of the river at key bathing sites for two scenarios: (a) during the entire 12-week Kumbh and (b) during the special Snans (bathing periods) scheduled for six nonconsecutive days ( WWF, 2013 ).

Non-negotiable water depth levels were recommended for the Kumbh festival, as was a restriction on discharges of untreated waste into the Ganga River. These flow recommendations aligned well with geomorphological and biological objectives of the environmental flow assessment ( WWF, 2013 ). In response, the state government of Uttar Pradesh agreed to allocate an additional 200–300 m 3 /s for the two-month duration of the Kumbh festival ( Lokgariwar et al. 2014 ). During 2013, monitoring efforts showed that recommended water levels were maintained for more than 90% of the festival’s duration. To the best of our knowledge, the Ganga River case was a world first in giving the spiritual status of a river the highest priority for determination and implementation of environmental flows. The magnitude and importance of the celebration of the Kumbh in 2013 called for action on environmental flows, and presented an opportunity to highlight the conservation challenges facing rejuvenation of the larger Ganga Basin ( WWF, 2017 ).

3.3 |. The Athabasca River, Canada

The Athabasca River, Canada, is linked intimately to the culture and economy of the Athabasca Chipewyan First Nation (ACFN) and Mikisew Cree First Nation (MCFN). The rights of these First Nation peoples to hunt, trap, fish, and otherwise exercise their rights—all activities linked to the Athabasca River and the Peace-Athabasca Delta, a massive wetland complex ( Timoney, 2013 )—were recognized in Treaty No. 8 of 1899. Candler, Olsen, and DeRoy (2010) documented the relationships of the ACFN and MCFN to the river, including their concerns over navigation and broader water quality and quantity issues related to their practice of Treaty rights. Their study aimed to understand the possible effects of river alteration to the practice of Treaty rights, such as limited access, reduced quality of lands or waters for subsistence use, and erosion of opportunities for transmission of knowledge. Beyond the functional uses of the river for mobility and economic practice, for First Nations the Athabasca River is a sentient being whose liveliness drives the flow of water through the area, as indicated in a comment from an ACFN representative:

“When we were younger the Athabasca River was … a wild beast. In other words, because it was alive, it had tremendous amount of water, it fed all the tributaries, lakes and everything. When the spring flood and that occurred … it brings life to the delta and when it brought life to the delta it also kept our people healthy, our population stable and, in other words, it sustained our way of life for our people for the existence of who we are today.” ( Candler et al., 2010 , p. 12).

The 2010 study was conducted in the context of ongoing upstream oil sands development, a changing climate, and overall declining flows ( Sauchyn, St-Jacques, & Luckman, 2015 ). Candler et al. (2010) found that reductions in the quantity and quality of the Athabasca River’s flow associated with oil sands development were having adverse effects on the ability of ACFN and MCFN members to access territories, and to practice their Aboriginal and Treaty rights. Interviews with male navigators revealed that use of the river for drinking water, trapping, and teaching seemed to have declined more than use for hunting, transportation, and cultural/spiritual and wellness practices. All respondents reported that the seasonal flow of the Athabasca had changed over their lifetimes.

Based on these findings, researchers advanced environmental flow recommendations in the form of two preliminary thresholds. The first threshold, an Aboriginal Base Flow (ABF), recommends water levels for the Athabasca River and adjacent streams that allow ACFN members to fully practice their rights and access their territories. The second, an Aboriginal Extreme Flow (AXF), defines a low water level for the river below which loss of access would cause widespread disruption of Aboriginal and Treaty rights along the river, its tributaries, and the delta. Based on recollections of land-users and the normal year hydrograph of the Athabasca River, researchers made conservative estimates of flow conditions for the ABF and AXF. The study recommended that the Crown “sit with” both Nations to establish an Athabasca River Consultation and Accommodation Framework to govern future water management. This governance model would include: linking water abstraction activity to the duties of the Canadian Government under the treaty to both consult and accommodate First Nations, setting a goal for frequency of spring floods and further monitoring and refinement of AXF levels and their social and ecological impacts ( Baines, Steelman, & Bharadwaj, 2017 ).

The Athabasca River case is emblematic of the widening of scope of environmental flows in its explicit recognition of the flow definitions and needs of First Nation peoples of Canada. Even the names of the recommended flows—Aboriginal Base Flow and Aboriginal Extreme Flow—leave little doubt regarding the intended beneficiaries of these water management guidelines. The ability to practice Aboriginal rights, as recognized in a historic Treaty, and the well-being of First Nation peoples in the Athabasca River are dependent on river flows ( Baines et al., 2017 ). Additionally, the Athabasca case represents an attempt to account for Indigenous worldviews and the quality of people-place relationships, a challenging task for environmental flow assessments ( Finn & Jackson, 2011 ).

3.4 |. Murray-Darling Basin, Australia

During the past few decades there has been a significant investment in scientific research to inform environmental flow assessments in Australia, including experimentation in approaches to determining the flow requirements of Indigenous peoples ( Jackson, Pollino, Maclean, Bark, & Moggridge, 2015 ). Indeed, Indigenous leaders have initiated research into “cultural flows”, a concept which they define as “ water entitlements that [would be] legally and beneficially owned by the Indigenous Nations of a sufficient and adequate quantity and quality to improve the spiritual, cultural, environmental, social, and economic conditions of those Indigenous Nations ” ( Weir, 2009 ).

Jackson et al. (2015) describe two multidisciplinary case studies conducted in Australia’s Murray–Darling Basin to understand Indigenous values and explore the application of methods to derive water requirements to meet them. Participants shared their water values with researchers who quantified a limited set of water requirements necessary to sustain those values and then assessed whether these water requirements would be met under three alternative water management scenarios, one of which would entail a substantial reallocation of water to the environment.

The first case concerns the Werai State Forest, part of the Murray River complex of wetlands recognized under the Ramsar Convention. The Werai is described as a special place for Wamba Wamba people: it is a place “ seen by most of the local community as home ” ( Jackson et al., 2015 , p. 146). There are 349 registered Aboriginal cultural sites in the forest ( Yarkuwa Indigenous Knowledge Centre Aboriginal Corporation, 2009 ). Title to the Werai Forest is due to be handed back to the Wamba Wamba and the area is to be managed as an Indigenous Protected Area. Restoring “cultural water” to the wetland is a priority of the community ( Weir, Ross, Crew, & Crew, 2013 ). Threatening this goal, however, are changes in the frequency and duration of flooding of the Werai forest due to alterations to land use and river regulation. Concerned about the poor condition of the forest, traditional owners told researchers that they sought a more consistent delivery of environmental water under a flow regime that restores a balance in vegetation communities and provides suitable habitats for fish and waterbirds. The results of this preliminary investigation have been used by traditional owners in their discussions with the Commonwealth agency that delivers environmental water to features of ecological significance, along with a private group that brokers environmental water delivery to wetlands.

The second case, from the northern Murray–Darling Basin, concerned a small billabong (oxbow lake) that fills periodically during flood flows and the nationally registered heritage fish traps at Brewarrina on the Barwon–Darling River. Prior to European settlement, the billabong area was an important tribal meeting place. Between 1876 and 1967 it was the site of the Brewarrina Aboriginal Mission and it is now listed on the State Heritage Register. Environmental protection is a priority for the Ngemba people that maintain rights and responsibilities to their territories. Sites of spiritual significance represent important sources of cultural inspiration while also providing opportunities for recreational and subsistence pursuits, such as fishing and collecting bush foods. Two elders described why these places are special to them and their responsibilities to the river and its life: “ all legends, stories are along the river, for example where the billabong meets the river: it’s where the spirits are ” ( Jackson et al., 2015 , p. 147). Further, the heritage fish traps, as well as various other sites along the river provide evidence of past occupancy. Ngemba traditional owners stated that water needed to be allocated to sustain the “life force” flow of the river, to connect the billabong to the river at times of high flow, and to enable local sustainable development enterprises. According to Ngemba participants, changing flow regimes were the main causes of decreasing water quality and habitat loss. Researchers employed semi-structured interviews, workshops, photo voice elicitation and mapping methods to define a set of hydrologic requirements that quantified an acceptable flow regime or particular flow demands ( Jackson et al., 2015 ).

These preliminary studies demonstrate how Indigenous knowledge, values and priorities can contribute to the setting of water requirements in the Australian context. They demonstrated the potential for environmental flow assessment methods ( Finn & Jackson, 2011 ; Poff et al., 2010 ) to address direct Indigenous uses of water. Nevertheless, further discussion is required among Indigenous communities, water planners, and eco-hydrology specialists to extend these methods to meet a wider array of less tangible Indigenous values.

3.5 |. Kakaunui and Orari rivers, New Zealand

Maori, the Indigenous people of New Zealand, have developed many innovative approaches to the comanagement of freshwater ( Harmsworth et al. 2016 ). Cultural Flow Preference Studies (CFPS) offer one approach that has been implemented across New Zealand to convey to decision makers how flow regimes affect Maori cultural interests ( Tipa & Nelson, 2008 ; Tipa, Nelson, Home, & Tipa, 2016 ). A CFPS represents a different way of thinking about the role of people in the setting of environmental flows, and a new way of conceptualizing how people react to rivers. It recognizes that people view a landscape and make judgments concerning the type and quality of experiences they expect to have and the ease of accessing, exploring, using and functioning in the environment they are viewing ( Chenge, 2007 ; Kaplan & Kaplan, 1982 ).

To develop the CFPS approach, Maori provided descriptions of river flows, river use, and the attributes that describe healthy vibrant rivers that support cultural beliefs, values, and uses ( Figure 3 ). From these descriptions, valued flow attributes formed the basis for field assessments. Cultural assessments of sites identified by Maori utilize a process akin to customer satisfaction assessments and environmental preference studies ( Tipa, 2010 ). Cultural flow preferences, and importantly the flow thresholds, are calculated for four themes: mahinga kai —gathering of foods and other materials for cultural use (up to nine attributes); Wai Maori —freshwater (four attributes); hauora —well-being (three attributes), and cultural landscapes (three attributes).

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(a) A tribal member completing a cultural assessment of a tributary of the Kakaunui River, New Zealand. (Photo: Kyle Nelson). (b) As part of the Kakaunui Cultural Flow Preference Study, tribal members chose to complement their cultural assessments with data about eel presence, collected through electrofishing (Photo: Myra Tipa)

We describe results of CFPSs in the Kakaunui and Orari river catchments in New Zealand ( Tipa & Nelson, 2012a , 2012b ). Through field visits, structured assessments, and observations, average scores for various flow attributes and for each of the four themes (i.e., Wai Maori, Cultural Landscape, Cultural Use, and Hauora) were determined at several sites in each catchment. These average scores were compared with average recorded river flows for the time and date of the assessment. Additional data were collected using experiential study methods, specifically personal interviews with tribal members, focus groups, the use of pictorial information, open ended questions, and cognitive mapping.

For the Kakaunui Catchment, the data confirmed that flows for one site in the Kakaunui Catchment (at Mill Dam) at or below 350 L/s were consistently scored as being unsatisfactory across all four themes. However, assessors also rated flows between 350 and 650 L/s as unsatisfactory and of concern for at least one of the themes. These initial analyses that consider the ratings for satisfaction and a weighting for the significance of each attribute suggested that the current minimum flow of 250 L/s could be considered too low by Maori ( Tipa and Nelson 2012b ). In the Orari River, the data suggested that Maori were highly unlikely to support a flow of less than 900 L/s because flows below this level exposed the riverbed, led to the accumulation of nuisance plants, and impeded fishing from Maori lands ( Tipa and Nelson 2012a ).

Flow conditions impact how Maori feel about a site. As kaitiaki (guardians), Maori are expected to ensure healthy condition of sites within their territories are available for all to engage with safely. However, when flows in the Kakaunui River were below 350 L/s for prolonged periods, Maori believed that the health of the sites prevented use; they did not believe that there was a good feel to the sites, and they were not proud of the condition of the sites. These feelings impact their cultural well-being. Maori also acknowledge a minimum flow is only one aspect of the flow regime. A range of flows, their timing, and duration all help determine whether or not a site supports cultural use and sustains ecosystems. Therefore, the flow assessment process is necessarily a partnership combining the expertise of biophysical and other scientists with the intimate knowledge and experience of Maori ( Tipa & Severne, 2010 ).

4 |. DISCUSSION

The above-mentioned cases represent early efforts to recognize, prioritize and incorporate the social and cultural importance of river flow regimes in environmental flow assessments. The purpose of this incorporation is to improve water management and governance by connecting human communities, satisfying spiritual and religious needs, and protecting Indigenous rights and well-being, in accordance with international human rights standards. Nevertheless, these cases only scratch the surface of the multitude of relationships between humans and rivers and the opportunities for incorporating them into environmental flows. We encourage further exploration of still under-recognized or hidden river flow values and dependencies. Examples might include the linkages between a river’s flow and: a sense of place, identity, subsistence resources, religious and ancestral belief systems, well-being, language or locally important narratives, and education practices, among others ( Table 1 ; Figure 4 ). We also urge wider acceptance and more explicit inclusion of diverse knowledge of rivers, not only limiting flow assessments to forms of expertise based on the hydrograph as the main framing principle. There are many examples of other ways of knowing or seeing rivers that are insightful for developing more sustainable and just interactions between societies and rivers. In the Amazon, rivers are central to the worldviews of Indigenous communities. Amazonian rivers can include features such as underwater cities which provide shelter to drowned relatives ( Fraser & Tello Imaina, 2015 ) and can sustain ancestors who protect water resources and whose existence is also influenced by flow ( Huertas & Chanchari, 2011 ). In north Australia, many Aboriginal traditions affirm the role of the Rainbow Serpent as driver of the hydrological cycle and bringer of the wet season floods ( Liedloff et al., 2013 ). In Africa, there is widespread belief in river Gods and spirits that have their own water requirements, often related to deep pools of clear water or waterfalls; these Gods can be angered by changes to flow regime through water infrastructure ( Breen, Jaganyi, Tham, & Zeka, 2006 ; Main, 1990 ; Siegel, 2008 ).

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For many human populations around the world, river flows are linked to livelihood, identity, sense of place, religious beliefs and ceremonies, language systems, or educational practices. These embedded, reciprocal, and constitutive relationships between humans and rivers remain poorly understood, but can be critically important to assessment and implementation of environmental flows

In these and other water knowledge and management traditions, riparian communities are keen to hold on to their custodial rights and responsibilities and would like to maintain their relationships with each other and with the river. How to reconcile such desires with national policies and legislation is still very much an open question. Further, a movement to recognize rivers as agents with lifegiving force and personality has taken hold in Colombia, New Zealand, and India ( Pecharroman, 2018 ). Granting legal personhood to rivers foregrounds reciprocal exchanges between people and rivers, emphasizing mutual responsibilities over narrow utilitarian definitions of human benefit from water and resource extraction ( O’Donnell & Talbot-Jones, 2018 ). These new frontiers of water governance represent promising avenues for improving the assessment and implementation of environmental flows within the blueprint of the renewed Brisbane Declaration and Global Action Agenda ( Arthington et al., 2018 ).

The cases described in this paper illustrate opportunities for the adaptation of existing environmental flow methodologies to achieve greater consideration of river-human relationships, but also underscore the relevance of new approaches that use social and cultural perspectives for framing sustainable ways of living with rivers that can perhaps complement or partly replace typical environmental flow assessments. These cases are also consistent in underscoring the need for interdisciplinary teams that include social scientists so as to draw on their knowledge and methods. Notwithstanding those advances, the majority of environmental flow approaches still retain a modernist ontological framing, one in which scientific knowledge defines the river as a natural or biophysical entity that can be objectively known. Cultural values and social relations appear at best as additional factors or dimensions that need to be incorporated in the biophysical framing of environmental flow assessments. In this prevailing framing, alternative (nonmodern) ways of engaging with, talking about, living with and indeed defining and knowing rivers are relegated to the realm of “culture.”

For the science and practice of environmental flows to advance according to the internationally-agreed definition and actions recommended in the 2018 Brisbane Declaration, there is a need for increased acceptance that the production of scientific knowledge about rivers is itself also a social and cultural process ( Johnston et al., 2012 ; Magdaleno, 2018 ). All scientific concepts are partial and historical, as Poff and Matthews (2013) acknowledge in their history of the evolution of environmental flows. In developing the natural flow paradigm ( Poff et al., 1997 ), an idea that has provided a solid conceptual basis for environmental flows, river flow was seen as one of many significant environmental variables but it came to be considered the “master variable” governing river ecosystem characteristics and functions. In another sense, flow was seen as a ‘master variable’ in the era of widespread dam construction, for it could most readily be controlled or “mastered” with the know-how of scientists and engineers and through the infrastructure that harnessed the power of water.

Realization of the renewed Brisbane Declaration ( Box 1 ) requires a rethink of relationships between humans and rivers. A crucial step will be for researchers and water managers to reflexively acknowledge the diversity of ways of knowing, relating, and utilizing rivers, to move towards more locally or contextually situated assessments and negotiations of environmental flows. This will lead to better recognition of the mutual interdependencies between humans and rivers, and support the development of effective approaches to foster more mutually beneficial modes of relating to rivers in situations where water extraction and river regulation threaten to undermine the health of rivers and their dependent human communities. Achieving this requires that assessment and negotiation processes allow sufficient time for full inclusion of all interests and for disempowered groups to be afforded opportunities to influence project scope and methods. The Brisbane Declaration’s accompanying Global Action Agenda offers guidance for continued advancement towards incorporation of river-human relationships in environmental flows, through recommendations for leadership and governance, management, and research. The greatest challenge may be to deepen, pluralize and diversify understandings of the relationships between humans and rivers, and place the acceptance that there are many different ways of seeing and knowing rivers at the core of environmental flow assessments and their implementation.

ACKNOWLEDGMENTS

Discussions at SESYNC that included Siva Sivaplan, Lisa Perras Gordon, Paul Lumley, and Jon Kramer helped inform material presented in this paper. We are grateful to the many people who participated in the case studies we describe and especially to Sarah Baines and Peter Esselman for review of material from the Athabasca and Patuca case studies, respectively. Special thanks go to Nadia Seeteram for her assistance with literature searches and reference management and to Ann Marshall for preparation of Figure 4 . The views expressed in this article are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency. The multidisciplinary and cross-regional collaboration that informed this paper was in large part supported by the National Socio-Environmental Synthesis Center (SESYNC) under funding received from the National Science Foundation DBI-1052875. S. Jackson was supported from a grant from the Australian Research Council’s Future Fellowships Program (project number FT130101145). M. Douglas was supported by the Australian Government’s National Environmental Science Program. C. Dickens recognizes Water, Land, and Ecosystems for support. E. Anderson acknowledges support from The MacArthur Foundation under grant agreements #16-1607-151 and G-106564-0. We thank Stuart Lane, Ryan Emanuel, and an anonymous reviewer for helpful comments that improved this manuscript.

Funding information

Australian Research Council, Grant/Award Number: FT130101145; John D. and Catherine T. MacArthur Foundation, Grant/Award Numbers: 16-1607-151, G-106564-0; U.S. National Science Foundation, Grant/Award Number: DBI-1052875

CONFLICT OF INTEREST

The authors have declared no conflicts of interest for this article.

Climate change may help the Colorado River, new study says

Researchers still recommend a conservative approach to river management..

(John Burcham | The New York Times) The Colorado River flows through the Grand Canyon in 2020. A new study predicts that the river's flows will increase between 2026 and 2050.

This article is published through the Colorado River Collaborative , a solutions journalism initiative supported by the Janet Quinney Lawson Institute for Land, Water, and Air at Utah State University.

A new study found that the Colorado River may experience a rebound after two decades of decreased flows due to drought and global warming.

“Importantly, we find climate change will likely increase precipitation in the Colorado headwaters,” Professor Martin Hoerling, the study’s lead author, wrote to The Salt Lake Tribune in an email. “This will compensate some if not most of the depleting effects of further warming.”

Recently published in the Journal of Climate , the study by researchers at the University of Colorado Boulder’s Cooperative Institute for Research in Environmental Science used data from the Intergovernmental Panel on Climate Change.

Researchers analyzed precipitation, temperature and flows at Lees Ferry, a point 15 miles downstream of Glen Canyon Dam in northern Arizona . Lees Ferry serves as the dividing line between the Upper and Lower Colorado River Basin.

Winter snows melting off mountains in the Upper Basin states of Colorado, New Mexico, Utah and Wyoming and into the river each year produce about 85% of the river’s flow.

The study’s climate projections forecast that there is a 70% chance that climate change will lead to increased precipitation in the Upper Basin between 2026 and 2050. That precipitation increase could boost the river’s flows by 5% to 7%.

The Colorado River’s flows have decreased by 20% since the turn of the century.

But researchers caution that these forecasts aren’t a bailout for the beleaguered river. Climate change will lead to a higher variability in precipitation, meaning that “extremely high and low flows are more likely” on the Colorado River between 2026 and 2050, according to the study.

“When there is that much uncertainty involved in something, the smartest management approach is to be conservative,” said Brian Richter, who serves as the president of Sustainable Waters, an organization focused on water education .

Richter, who was not involved in the University of Coloraro study, recently authored a different study about where the Colorado River water goes from its headwaters to its dry delta in Mexico.

“That there might be better precipitation is good to know,” he said, “but it’s not cause to abandon the reality that we need to aggressively reduce our level of consumption.”

Water managers across the West are currently working to negotiate management of the Colorado River and its reservoirs after 2026 , when current operational guidelines from 2007 expire. The Bureau of Reclamation, the federal agency that oversees water projects across the country, aims to complete a draft environmental impact statement for post-2026 operations by the end of this year.

Hoerling, too, pointed to the need for more responsible river use as water managers hash out future river guidelines: “The crisis, though triggered at this time by nature, exposed a structural problem of how water is used, especially in the Lower basin of the Colorado River.”

Arizona, California and Nevada — the Lower Colorado River Basin states, which draw their water from reservoirs — have committed to water cuts . The Upper Basin states argue that they shouldn’t have to cut their water use because they experience natural water cuts due to the river’s decreasing flows and evaporative losses.

Hoerling wrote that, given a warming planet and highly variable river conditions responsible management necessitates more research on how low the Colorado River’s flows could be in the future.

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Remote sensing inversion on heavy metal content in salinized soil of Yellow River Delta based on Random Forest Regression—a case study of Gudao Town

Pingjie Fu 1 ,
Xiaotong Li 1 ,
Jiawei Zhang 1 , 2 ,
Chijie Ma 1 ,
Yuqiang Wang 3 &
Fei Meng 1

Scientific Reports volume 14 , Article number: 11216 ( 2024 ) Cite this article

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Environmental sciences
Environmental social sciences

To explore the potential of using the mineral alteration information extracted by remote sensing technology to indirectly estimate the heavy metal content of salinized soil, 23 sampling points were uniformly set up in the town of Gudao in the Yellow River Delta as the research area in 2022. The concentrations of seven heavy metals, Cr, Cu, Pb, Zn, As, Mn and Ni, at the sampling points were determined in laboratory tests. Spectral derivative indices, topographic factors, and mineral alteration information (iron staining, hydroxyl, and carbonate ions) were extracted and screened as modeling factors using Sentinel 2 imagery. An inverse model of heavy metal content was constructed using the random forest algorithm, and the model accuracy was evaluated using the cross-validation method. The results of the study show that: (1) Hydroxyl and carbonate ion alteration can be effectively used for the inversion of soil As and Ni content in this study area. Iron-stained alteration can be used as a modeling factor in the inversion of Cr, Cu, Pb, Zn, and Mn concentrations. (2) The inclusion of alteration information improves the accuracy of heavy metal content inversion. The Cu concentration was verified to be the best predictor, with an RMSE of 3.309, MAPE of 11.072%, and R 2 of 0.904, followed by As, Ni, and Zn; the predictive value of Mn, Cr and Pb was average. (3) Based on the results of concentration inversion, the high concentration areas of As, Ni, and Mn are primarily distributed on both sides of the river and around lakes and ponds. The high-concentration areas of Zn were mainly distributed in the farmland areas on both sides of the river. Areas with high concentrations of Cu were mainly distributed in the eastern oil extraction area, both sides of the rivers, and around lakes.

Introduction

Soil salinization has a serious impact on the ecological environment of the Yellow River Delta wetlands. In recent years, the sediment entering the Yellow River has decreased sharply, and the rate of seawater erosion has changed, resulting in the shrinkage of the wetlands due to seawater backwater, which has aggravated the salinization of the delta soils. To some extent, it constrains the development of local agriculture. Simultaneously, deepening salinization leads to increased soil vulnerability. Human activities such as oil production and mining have resulted in some heavy metals entering coastal beaches. According to the data from the 2019 ecological geochemical survey of the lower Yellow River Basin in Shandong Province, the contents of the heavy metals As, Cr and Ni in the soils within Dongying City exceeded the surface soil elemental background values for this heavy metal element in Shandong Province. Although As is not a heavy metal, it is usually included in the category of heavy metals for discussion because its behavior and source as well as its harm are similar to those of heavy metals. According to previous studies, most of them used the concentration of heavy metal elements such as Cu, Pb, Zn, Cr, Ni, Mn, Cd, and Hg as important indicators of soil quality 1 , 2 . Therefore, Cu, Pb, Zn, Cr, Ni, Mn, and As were selected as inversion objects in this paper to provide technical support for the in-depth study of the spatial distribution and large-scale monitoring of heavy metal concentrations in salinized soils in the Yellow River Delta. It can provide a scientific basis for ecological environmental protection, land quality management, rational use of resources, and agricultural production in the region.

In recent years, researchers have studied a variety of methods for monitoring soil heavy metal content in typical areas. Examples include direct assessment using the sample analysis method 3 , X-ray fluorescence (XRF) in situ detection 4 , pollution evaluation and source analysis 5 , spatial distribution of GIS methodologies, and inversion of heavy metal content in multi-source remote sensing images 6 , 7 . As an advanced Earth observation technology, remote sensing has the advantages of objectivity and reality, long time series, large area, low cost, simplicity high efficiency. Combined with the rapid development of computer technology, this technology, and plays an important role in the assessment of heavy metal content in soil. Hyperspectral remote sensing data have a high spectral resolution. The accuracy of soil heavy metal quantitative inversion can be improved by optimizing feature extraction 8 , band combination 9 , and training models 10 . Among these, spectral data obtained using portable ground object spectrometers have high accuracy, which is convenient for model construction and mechanism analysis. However, achieving model transposition for large-scale images is difficult. Satellite-based hyperspectral data facilitate large-area monitoring but often require complex data preprocessing because of limitations in spatial resolution and signal-to-noise ratio. Guo et al. used the DS algorithm to correct the Zhuhai-1 hyperspectral image to match the laboratory spectrum. Then the Cr in soil was predicted based on the combined SNV + UVE + SVR model, and the inversion was effective 11 . Sun et al. inverted the Zn content by extracting the characteristic bands of organic matter and clay minerals that adsorb the soil heavy metal Zn. The results showed that VNIR hyperspectral data were superior to VNIR-SWIR hyperspectral data in predicting and localizing Zn concentrations in soil 12 . Airborne hyperspectral data solve the problems of spatial resolution and data accuracy, enabling high-precision inversion of soil heavy metal contents at a small scale. However, the cost of data acquisition is high, and the maintenance cycle of the instrument is long. Multispectral remote sensing imagery is advantageous in terms of spatial resolution, processing efficiency, time series of available data, and cost. Current research mainly focused on constructing an inversion model of soil heavy metal content by extracting and screening the characteristic bands, spectral derivative indices 7 , 13 , 14 , and topographic factors (DEM, slope, and aspect) of heavy metal concentrations. Yang et al. proposed a network model based on transfer learning theory and a back propagation (BP) network optimized by genetic algorithm (GA). The visible and near-infrared spectral data from Landsat8 satellite images, and modeling factors selected by the digital elevation model were used to predict Cu and Pb contents. The results show that the proposed Tr-GA-BP network performs well 15 . Wang et al. proposed an optimization of the commonly used partial least squares regression (PLS) method to invert the Ni, Cu, and Zn contents of tailings ponds and their surroundings by using a variety of remote sensing indices and the modeled heavy metals as modeling factors based on GF-2 image. Compared to the traditional PLS, the goodness-of-fit of Ni, Cu and Zn was improved by 0.0852, 0.2291 and 0.2919, respectively 16 . Iron oxides and clay minerals have a certain adsorption effect on soil heavy metals 17 . Iron-stained, hydroxyl (–OH), and carbonate ion (CO 3 2− ) alteration information can reflect the distribution of the two types of minerals, and the technology of alteration mineral information extraction based on remotely sensed images is very mature 18 , 19 . However, the alteration of mineral information has not yet been applied to the image inversion of soil heavy metal content. Yang et al. extracted mineralization and alteration information in the Xinjiang Tashkurgan Prefecture area using mineral indicators and mask models based on ASTER images. Statistical analysis with existing geological data identified three mineralized prospecting targets 20 . Zhang et al. used the GF-5 visual infrared spectroscopic imager (VIMS) to extract iron staining and hydroxyl alteration. It was found the alteration information extracted from VIMS image is consistent with the alteration extracted from TM image, and it is more accurate 21 . Sentinel-2A satellite data has more advantages in spatial resolution and spectral resolution than Landsat series images. Li et al. used Sentinel-2A satellite data to analyze the spectral combination responses of different types of alteration, and then selected the optimal principal component analysis scheme to extract alteration information 22 . According to previous studies, the extraction of alteration information is dominated by methods such as band ratio, principal component analysis, and independent component analysis (ICA) 23 , 24 . In particular, the principal component analysis method has the advantages of simple realization, fast speed, good effectiveness, and robustness, which make a significant contribution to the extraction of alteration information 25 .

To investigate the potential of alteration information in the inversion of heavy metal content in salinized soils, this study used the town of Gudao in the Yellow River Delta as the research area to obtain seven heavy metal concentrations of soil Cr, Cu, Pb, Zn, As, Mn, and Ni from 23 sampling points. Sentinel-2A satellite imagery and spectral derivative indices, topographic factors, and alteration information to extract and screen modeling factors. A random forest regression model was constructed to predict soil heavy metal content, and the accuracy of the estimation results was evaluated. To investigate the effectiveness of mineral alteration information extracted from multispectral remote sensing images in soil heavy metal inversion, with a view to providing new ideas and methods for rapid and efficient large-area soil quality monitoring, and to improve the technical level of multispectral remote sensing in support of soil environmental quality research.

Overview of the study area and data acquisition

Overview of the study area.

The study area was the town of Gudao, northeast of Dongying City, Shandong Province, China, located in the Yellow River Delta. Surrounded by the Bohai Sea in the north and the Laizhou Bay in the east, with the geographical coordinates of 118° 39′–119° 8′ E and 37° 47′–37° 84′ N, it has a total area of 159.46 square kilometers and is separated from the Jiaodong Peninsula by the sea (Fig. 1 ). The town is located in the semi-arid warm-temperate East Asian monsoon zone, through the statistics of meteorological data from 2001 to 2020, in which the average annual temperature is 12.1 °C, 12.9 °C is the highest average annual temperature and 10.9 °C is the lowest average annual temperature, an annual precipitation of 347–813.2 mm, and an annual sunshine of 2600–2800 h. Underground oil resources are rich, and the soil above the ground is fertile and well-irrigated, making it suitable for growing crops such as rice, wheat, corn, and soybeans. The traffic is well-developed, and the internal roads are vertically and horizontally aligned.

Geographic location of the research area.

Data acquisition and preprocessing

Soil sample data

Soil samples were collected in the field on July 25–27, 2022 in Gudao, and were mainly distributed in the eastern part of the study area in the oil extraction area, in the central part of the agricultural area, and to a lesser extent, on the sides of riverbanks and pits, at 23 sampling sites. Surface weeds and stones were removed by digging to a depth of 0–30 cm using a shovel. Soil samples were collected in polyethylene plastic bags weighing approximately 2.5 kg per sampling point. Using a Global Navigation Satellite System (GNSS) receiver to receive signals from a continuously operating reference station (CORS), and using Real-Time Kinematic (RTK) method to locate the sampling point, the coordinate system is WGS-84. Sealed bags are labeled with the time of sampling, latitude and longitude, and sample number. Transportation in black plastic bags protected from light at the end of sampling. Afterwards, the collected samples are sent back to a professional testing organization for testing. First, the samples were removed from impurities such as stones and plant fragments. Then, soil samples were dried after natural air drying, grinded with a glass rod and passed through a 100 mesh nylon aperture sieve, and placed in clean sample bags. A German-made wavelength dispersive X-ray fluorescence spectrometer (Bruker S8 TIGER) was utilized for the detection of heavy metal elements in soil samples. The metal element concentrations were detected using wavelength-dispersive X-ray fluorescence spectrometry (HJ780-2015). The detection limits were 3.0 mg/kg for Cr, 10.0 mg/kg for Mn, 1.5 mg/kg for Ni, 1.2 mg/kg for Cu, and 2.0 mg/kg for Zn, As, and Pb.

The numerical characteristics of the seven metal elements were determined based on the results of the laboratory tests. The extreme values, arithmetic means, and standard deviations of the metal contents were selected as statistical indicators and compared with the background values of soil chemistry in Dongying City. The calculated comparisons showed that the percentages of samples with Cu, Pb, Zn, Cr, Mn, As, and Ni contents exceeding the soil chemical background values in Dongying were 0%, 10%, 2.5%, 5%, 0%, 7.5%, and 10%, respectively. Based on the distribution of metallic elements in the study area, a histogram rectangle with group distance as the bottom edge and frequency as the height was plotted to show the content of each metallic element at the 23 sampling points and the exact distribution of the elements (Fig. 2 ).

Elemental content histograms.

Remote sensing image data

The Sentinel-2A satellite was launched on June 23, 2015, using a Vega launch vehicle carrying a multispectral imager. It is a high-resolution multispectral imaging satellite with an altitude of 786 km, coverage of 13 spectral bands, three types of spatial resolution (10, 20, and 60 m) and a width of 290 km. Sentinel-2A imagery combines the strengths of the Landsat and Spot satellites with high-resolution multispectral features and relatively stable quality. Therefore, in this study, Sentinel-2A data on October 23, 2022 were selected for an inversion study of soil heavy metal content in the Yellow River Delta region. Images covering the entire study area were downloaded from the official website of the European Space Agency. The downloaded Sentinel-2A remote sensing images were imported into SNAP and exported in ENVI format after 10 m resampling. Band fusion is performed on the exported files in the ENVI platform to obtain remote sensing images displayed in real bands. As the Sentinel-2A remote sensing imagery acquired is at the L2A level and have been processed for radiometric calibration and atmospheric correction, and only cropping was required before image processing and analysis. Water disturbance information was extracted by MNDWI, and band3 and band11 were selected to participate in the calculation. A segmentation threshold of − 0.12 < WNDWI < − 1 was used to create a water mask file, and the image was masked using the mask file.

Theory and methodology

Modeling factors.

Spectral derivative indices

Various vegetation covered on the ground absorbs some heavy metal elements from the soil during its growth process, as well as soil moisture, brightness, and color, can affect satellite sensors to a certain extent when they receive reflected waves from the ground. Currently, the use of vegetation indices to invert land-cover change is gradually becoming an important research tool for understanding global environmental change 26 , 27 . Therefore, in this study, a variety of spectral indices reflecting the surface conditions, also known as spectral derivative indices, were selected to enhance specific information in remote sensing images.

The spectral derivative indices selected for the study were the Normalized Difference Vegetation Index (NDVI), Clay Mineral Ratio (CMR), Modified Normalized Difference Water Index (MNDWI), Ratio Vegetation Index (RVI), Difference Vegetation Index (DVI), modified soil-adjusted vegetation index (MSAVI), Enhanced Vegetation Index (EVI), and Red-Green Ratio Index (RGRI), as shown in Table 1 .

Topographic factors

The ASTER GDEM Digital Elevation Model (DEM), which covers the entire study area at a resolution of 30 m, was downloaded from the Geospatial Data Cloud website. The ASTER GDEM is an easily accessible, high-precision DEM that covers virtually all of the Earth's landmass and is available to all users, regardless of the size or location of their target area. The DEM data were further used for terrain factor extraction, including aspect and slope.

Alteration information

The alteration of surrounding rocks refers to the process by which rocks and minerals undergo changes to their original physical and chemical properties due to hydrothermal activity, leading to the formation of new mineral assemblages 33 . Iron oxides and clay minerals have a certain accompanying relationship with heavy metals in soil, and information on iron-stained alteration, –OH, and CO 3 2− alteration may reflect the distribution of the two types of minerals. Principal component analysis (PCA) is one of the most commonly used methods for the extraction of alteration information. This is the process of reducing the correlation between images using a linear transformation to represent the information in each band with the fewest comprehensive indicators, thus highlighting the useful information contained in the image. By performing PCA on the water masked image, the information is mainly concentrated in the first component so that the magnitude of the contribution of the generated principal components can be reflected in the magnitude of the eigenvector matrix weights 34 , 35 . After specifically analyzing the actual situation of the study area, we chose to extract iron stained, –OH, and CO 3 2− alteration information.

In 1978, Hunt et al. found that minerals containing ions or ionophores such as Fe 2+ , Fe 3+ , –OH, and CO 3 2− have unique absorption properties in the visible-near-red band by examining the reflectance spectral characteristics of minerals 36 . With the help of rock and mineral spectral curves obtained from the U.S. Geological Survey (USGS) standard spectral library, the characteristic absorption peaks of the iron-stained minerals occur at 0.40–0.50 μm, 0.80–0.92 μm, 1.39–1.41 μm, and 1.90–1.92 μm, and the characteristic reflectance peaks are mainly distributed at 0.65–0.72 μm, 1.23–1.30 μm, and 1.60–1.70 μm. The characteristic absorption bands of –OH and CO 3 2− ionophores were generally distributed at 0.86–0.98 μm, 1.32–1.44 μm, and 2.15–2.55 μm, in which the most significant absorption feature was located at the vicinity of 2.33 μm, and the characteristic reflectance bands were mainly distributed at 0.49–0.58 μm, 1.60–1.70 μm, and 2.00–2.14 μm.

Based on the spectral characteristics of iron-stained minerals, after multiple band selections, two absorption bands at 0.40–0.50 μm and 0.80–0.92 μm, as well as two reflection bands at 0.65–0.72 μm and 1.60–1.70 μm were selected. These correspond to bands 2, 8, 4, and 11 of Sentinel-2A imagery, respectively. PCA (Table 2 ) was performed to extract information related to the alterations in iron staining. Based on the characteristics of the eigenvectors of the anomalous principal components, the absolute values of the loading coefficients for bands 2 and 4 must be relatively large and have opposite signs: one negative and one positive. Additionally, the loading coefficients for bands 8 and 11 should have opposite signs: one negative and one positive. By analyzing the PCA eigenvector matrix of the Sentinel-2A images in the study area, the loading coefficients of bands 2, 8, 4, and 11 in the principal component of PC4 were found to be consistent with the requirements. Thus, we conclude that the iron-stained alteration information was located in the PC4 component.

Based on the spectral characteristics of –OH and CO 3 2− minerals, two absorption bands of 0.86–0.98 μm and 2.15–2.55 μm, and two reflection bands of 0.49–0.58 μm and 1.60–1.70 μm, corresponding to bands 8, 12, 2, and 11 of the Sentinel-2A image, were finally selected by several band selections and were subjected to PCA (Table 3 ) to extract the –OH and CO 3 2− alteration information. Depending on the characteristics of the eigenvectors of the anomalous principal components, the signs of the loading coefficients of band 2 and band 8 should be opposite: one positive and one negative, and the signs of the loading coefficients of band 11 and band 12 should also be oppositive: one positive and one negative. The results of the analysis presented in Table 3 show that the loading coefficients of bands 8, 12, 2, and 11 in the PC4 principal component of the Sentinel-2A image in the study area meet the requirements. Therefore, the –OH and CO 3 2− alteration information of the Sentinel-2A image of Gudao Town was also determined to be located in the PC4 component.

Complex covariance test

A strong correlation between the factors distorts the model estimation. Therefore, the above factors must be tested for complex covariance to prevent the existence of serious complex covariance among them.

The Variance inflation test (VIF) was used to test the linear correlation between the factors. The formula is as follows:

The test statistic used to examine the explanatory ability of the model is R 2 (sample decidability coefficient). The magnitude of R 2 determines the degree of correlation between factors. A smaller R 2 value indicates that this factor is less linearly correlated with the other factors. If the VIF value is greater than 5, it indicates the presence of multicollinearity; if the VIF value is greater than 10, it indicates the presence of severe collinearity and the factor needs to be discarded.

Random Forest Regression model (RFR model)

Random Forest Regression (RFR) is the combination of multiple CART decision trees as weak learners to form a "forest" to make predictions on a dataset 40 . A single decision tree can only take a single classifier when making decisions, which inevitably results in disadvantages, such as the decision tree being able to select only one type of attribute to analyze at a time or overfitting the model to accommodate noise. To address these shortcomings, the algorithm builds a forest using randomization, in which the decision trees in the forest are not associated with each other. Multiple decision trees constructed to average errors and improve prediction accuracy are the core concepts of random forests.

To determine the accuracy of the model, three accuracy indicators used in this study were root mean square error (RMSE), mean absolute percentage error (MAPE), and R 2 .

RMSE is the square root of the ratio of the square of the deviation of the predicted value from the true value to the number of observations, which is of the same order of magnitude as the true value; it measures the deviation of the predicted value from the true value and is more sensitive to outliers in the data. The formula is as follows:

MAPE is the average of the deviation of the predicted value from the true value and the absolute value of the true value, and is a relative metric that is commonly used as a statistical measure of prediction accuracy. The formula is as follows:

The R 2 statistic is an important measure of the goodness-of-fit of the model and is calculated as the ratio of the regression sum of squares to the total sum of squares. The numerical values reflect the relative contributions of the regression. The formula is as follows:

The range for RMSE and MAPE values is [0, + ∞); when the gap between the predicted and true values is smaller, the closer the value is to 0, the higher the model accuracy; therefore, the smaller the RMSE and MAPE values of the model, the higher the model efficacy. Compared to RMSE, MAPE provides a more realistic reflection of the deviation between the predicted and actual values, presented as a percentage to enhance user understanding. However, the calculation is limited when the actual values are close to or equal to zero. By contrast, RMSE is applicable to any dataset and is more sensitive to outliers in the data. The R 2 value ranges from 0 to 1, with values closer to 1 indicating a higher model accuracy and stronger predictive capability.

Results and analysis

Modeling factor extraction and screening.

The correlations between the contents of the seven heavy metals were analyzed to obtain a comparable matrix of correlation coefficients, indicating a correlation between the variables (Fig. 3 ). Figure 3 shows that the correlations of As, Mn, Ni, Cu, and Cr were better.

Correlations between heavy metal content.

Spectral data, including six spectral bands and eight derived spectral indices, were extracted from the Sentinel-2A image of Gudao and analyzed for correlations between the concentration of each heavy metal and the spectral data (Table 4 ). As shown in Table 5 , the correlation between the elemental concentrations of Mn, Ni, As, Cu, and Zn and the six spectral bands was better, whereas the correlation between Pb and Cr and the six spectral bands was worse. Regarding spectral indices, the elemental concentration of Mn correlated well with MSAVI, MNDWI, RGRI, and NDVI, and the concentration of Ni correlated well only with MNDWI; all eight spectral indices correlated well with As, and the elemental concentrations of Cu and Zn correlated well with MSAVI, MNDWI, and RGRI.

The topographic factors included DEM, aspect and slope, and the correlation between the concentration of each heavy metal element and the topographic factors was calculated separately (Table 5 ). The coefficients in Table 5 show that the concentrations of six metal elements (Mn, Ni, As, Cu, Zn, and Cr) had the best correlation with aspect, that is they had the greatest effect on the metal elements, and the concentration of Pb had the best correlation with slope. However, the correlation coefficients of each terrain factor with metals were relatively low, and other factors must be considered in the subsequent selection of the modeling factors to select the most appropriate terrain factor.

Sentinel-2A images of the study area were processed using PCA to extract the PC4 component that could reflect the alteration information and analyze the correlation between the concentration of each heavy metal element and the alteration information (Table 6 ). From the data in Table 7 , it can be seen that, overall, the concentrations of five metal elements, Mn, Ni, Cu, Zn, and Cr, were well correlated with iron-stained alteration, and As and Pb had good correlations with –OH and CO 3 2− alteration. However, the correlation coefficients between the concentration of each metal element and the alteration information did not differ significantly from each other.

According to the results of the above correlation analysis, modeling factors with higher correlation coefficients were screened for the complex covariance test by comprehensively considering the spectral information, topographic factors, and mineral alteration information. Factors with VIF values greater than 10 were discarded, and the final modeling factors that were retained are listed in Table 7 .

Inverse modeling of soil heavy metal content

The original data is first randomly divided into training and validation sets in the ratio of 7:3. For the modeling factors selected for each heavy metal element in the study area, the RFR algorithm was used to construct an inverse model of the soil heavy metal concentrations in the region. The inversion results are listed in Table 8 . As shown in Table 8 , the prediction accuracy of the concentration of each element was improved by adding alteration information. The elemental concentration of Cu was predicted to be the best with an RMSE of 3.309, MAPE of 11.072%, and R 2 of 0.904. This was followed by As, Ni, and Zn, all with R 2 greater than 0.5 and significantly lower RMSE and MAPE. Although the prediction of the elemental concentrations of Pb, Cr, and Mn was improved by adding the alteration information, the prediction accuracy remained average. The analysis revealed that the low prediction accuracy of Cr and Pb may be due to the presence of a high number of outliers in the prediction model.

The corresponding scatter plots were obtained by comparing the measured values with the predicted concentrations of each heavy metal in the study area (Fig. 4 ). Statistical analysis of the predicted and measured values revealed that the inclusion of alteration information improved the accuracy of the model, and the prediction results were more stable. The scatterplot of the total sample shows that the closer it is to the y = x line, the better the model fit. The sample-predicted and measured values of the RFR model with the addition of alteration information were mostly concentrated around the 1:1 line, and the model fitting was superior to that predicted by the model without the addition of alteration information.

Comparison of the accuracy of inversion models for heavy metal concentrations.

Spatial distribution of soil heavy metal content

The spatial distribution of heavy metal concentrations was estimated using the constructed RF model based on spectral derivative indices, topographic factors, and alteration information after screening for the seven heavy metal elements in the study area. The inversion results are shown in Fig. 5 . The analysis results showed that the spatial distribution of the elemental concentrations of As, Ni, and Mn was generally consistent, with the high-concentration areas mainly distributed along the banks of rivers, lakes, and pits, followed by higher concentrations in the eastern oil extraction areas and lower concentrations in the agricultural areas. The Yellow River carries a large amount of sediment downstream from its source, and some of the sediments form piles along the banks. High concentrations on both sides of the river and around the lake may be due to compound industrial and agricultural pollution upstream, which causes heavy metals to accumulate. As a whole in the study area, heavy metal Cu concentrations in soils are low in the northwestern and central regions. The high-concentration area of Cu is mainly concentrated in the eastern oil extraction area, both sides of the river, and around the lake. Among them, the distribution of Cu in the soil of the eastern oil extraction area is continuous and the concentration is significantly higher than that in other areas. It is presumed that the Cu pollution in the area is related to the oil and gas development of the oil extraction plant. The areas with high concentrations of Zn were mainly distributed in the farmland areas on both sides of the river, with an overall trend of high in the southwest and low in the northeast. A combination of images and field surveys revealed that the southwestern side of the study area is mostly dominated by agricultural fields, suggesting that the high concentrations of Zn in the soil are likely to come from agricultural production practices. Areas with high concentrations of Cr and Pb were more widely distributed, with lower concentrations only in some of the pits and ponds. Both have a continuous distribution of heavy metal content in the soils of the area, with higher contamination on both sides and in the center. The spatial distributions of the concentrations of the seven elements matched well with the results of the correlation analysis. The distribution of the Cr elemental concentration is quite different from that of As, Ni, Mn, and Cu, which is attributed to the low accuracy of the prediction model for the Cr elemental concentration.

Spatial distribution of heavy metal element concentrations from Random Forest Modeling.

Except Cr element, the spatial distribution maps of the concentration of the remaining six heavy metal elements based on spectrally derived indices, topographic factors and alteration information using RF model are similar to the spatial distribution maps of the metals obtained by Yu et al. 41 . using the kriging interpolation method. The feasibility of using mineral alteration information extracted based on remote sensing images for predicting heavy metal content is again demonstrated. Moreover, the spatial distribution maps of heavy metal element concentrations obtained based on this paper's method are more detailed than those obtained based on the Kriging interpolation method. In terms of the drivers of heavy metal aggregation, the causes of Cu, Pb, and Zn aggregation analyzed in this paper have similarities with the sources of Cu, Pb, and Zn aggregation analyzed in the study by Zhang et al. 42 . It provides a more scientific basis for further monitoring the heavy metal content of soil on a large scale and strengthening regional land quality management.

Conclusions

This study used the town of Gudao in the Yellow River Delta as the study area and obtained seven heavy metal concentrations from 23 sampling points through on-site sampling and analysis. Based on Sentinel-2A images, spectral derivative indices, terrain factors, and mineral alteration information were extracted and filtered. A soil heavy metal concentration inversion model was constructed using the RFR algorithm, and the accuracy of the model was evaluated to achieve the spatial distribution inversion of heavy metal concentrations within the region. The results of this study are as follows:

–OH and CO 3 2− alterations can be effectively used for the inverse modeling of soil As and Ni contents. The RMSE and MAPE metrics of the prediction model were significantly reduced, and the R 2 improved from 0.2 to more than 0.5. Improvement of prediction by applying iron-stained alterations to Cr, Cu, Pb, Zn, and Mn elemental concentration inversion. In particular, the prediction accuracy of Cu elemental concentration was significantly improved with an RMSE of 3.309, MAPE of 11.072%, and R2 of 0.904, followed by elemental Zn with an RMSE of 5.065, MAPE of 8.01%, and R2 of 0.523, whereas the accuracy of Mn, Cr, and Pb improved and remained at a low level. However, for the entire sample, the correlation between the measured and predicted values of Mn was better, and the low prediction accuracy of Cr and Pb may have been due to the existence of points with higher concentrations.

The spatial distribution of soil heavy metal concentrations in the study area was inverted based on the constructed model. It was found that the areas of high concentration of As, Ni and Mn elements were mainly located on the banks of rivers, around lakes and ponds, followed by higher concentrations in the eastern oil extraction areas and lower concentrations in the agricultural areas. The high-concentration area of Cu is consistent with the distribution of the high-concentration areas of the above three elements, mainly in the eastern oil extraction area, both sides of the river, and around the lake. Areas with high Zn concentrations were mainly located in agricultural areas on both sides of the river. High concentrations of Cr and Pb are distributed over a wide area, with lower concentrations found only in some areas of the pits. The results of this study provide a scientific basis for the assessment and management of soil quality. For the perimeters of points with abnormally high heavy metal concentrations, further research is required in terms of field investigation, data analysis, and model construction. The number of sampling points can be increased and the range can be further expanded so that more data can be used for modeling and the applicability of the model can be improved. Meanwhile, at the level of spectral response mechanism, the correlation study between heavy metal elements and alteration information needs to be further deepened.

Data availability

The datasets generated during the current study are not publicly available due the procedures established in contract with the funding institution but are available from the corresponding author on reasonable request.

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This research is supported by the National Natural Science Foundation of China (No.42101388), Shandong Top Talent Special Foundation(No.0031504), Youth Innovation Team Project of Higher School in Shandong Province (No.2022KJ201), and Jinan City school integrated development strategy project (JNSX2023065).

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Pingjie Fu, Xiaotong Li, Jiawei Zhang, Chijie Ma & Fei Meng

College of Geodesy and Geomatics, Shandong University of Science and Technology, Qingdao, 266590, China

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Disaster Reduction Center of Shandong Province, Jinan, 250101, China

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P.F. conceptualization, data curation, funding acquisition, formal analysis and writing-original draft, review and editing. X.L. data curation, writing—review and editing. J.Z. data acquire and method design. C.M. literature review and method writing. Y.W. review, and editing. F.M. method design and funding.

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Fu, P., Li, X., Zhang, J. et al. Remote sensing inversion on heavy metal content in salinized soil of Yellow River Delta based on Random Forest Regression—a case study of Gudao Town. Sci Rep 14 , 11216 (2024). https://doi.org/10.1038/s41598-024-62087-y

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Received : 01 February 2024

Accepted : 13 May 2024

Published : 16 May 2024

DOI : https://doi.org/10.1038/s41598-024-62087-y

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Today’s front page, Wednesday, May 15, 2024

today's front page businessmirror 051524

Transport fix: Ferry system on Pasig River, 3 waterways

Cai U. Ordinario
May 15, 2024
3 minute read

THE national government is keen on maximizing Metro Manila’s natural resource, the Pasig River, to help ease commuters’ transportation woes.

Department of Transportation (DOTr) Assistant Secretary for Planning and Project Development Leonel Cray De Velez told reporters on Tuesday that they are already conducting a feasibility study on the project.

Once the study is completed, the agency will bid out the contract to develop the Manila Bay-Pasig-Marikina-Laguna lake ferry system by next year.

“It’s to provide an alternative east-west transportation corridor in NCR. So as you know, we have the North-South Commuter Railway, we have the subway. If you see the maps, those are primarily north-south corridors,” de Velez said.

“We do not have what we call east-west corridors for mass transportation and Pasig River naturally is there and traverses east-west. So unlike a railway where we still have to build the tracks, for the Pasig River, it’s there. All we need to do is build stations and also buy ferries. So it’s naturally there already and we hope to take advantage of that,” he explained.

De Velez said the DOTr is working with the Public-Private Partnership (PPP) Center on what is called the Manila Bay, Pasig River, Marikina River, and Laguna Lake ferry system.

He said this is part of the initiative of the President and the First Lady to enhance the Pasig River and “make it livable again.” The project also aims to create good walking spaces and help enhance urban development nationwide.

The feasibility study for the project is being conducted to gather information of the possible number of passengers who can take the ferry. This is crucial in determining the stations and how many stations will be created.

Currently, de Velez said, anecdotal evidence indicates that a lot of Filipinos living in Marikina and Rizal travel to the University Belt and the Central Business Districts like Makati.

But these are merely “anecdotal” evidence. “Until we have quantifiable studies and surveys, these are all anecdotes. So that’s what we’re doing right now. We’re figuring out how many people will actually use the ferry service in the future,” de Velez said.

Once the feasibility study is completed this year, the project will be submitted for evaluation of the interagency Investment Coordination Committee (ICC) and approval by the National Economic and Development Authority (Neda).

“A big focus of the administration is to use private expertise, private capital, and private efficiency to be able to develop our transportation system,” de Velez said.

Part of the study includes the use of electric ferries as well as the possibility of allowing bicycles on board these ferries. This is also consistent with the government’s efforts to encourage active transport.

De Velez said the interconnectivity of the Pasig ferry system is one of the primary concerns of commuters in terms of maximizing its use.

“One of the things we are considering is allowing bikes on board. So that’s one possibility as well, rather than having mga bike racks,” de Velez said. “So there are two options…these are having bike racks on the station or allowing bikes inside the public utility vessels or vehicles.”

Earlier, Department of Human Settlements and Urban Development (DHSUD) Secretary Jose Rizalino L. Acuzar, who also heads the Inter-Agency Council for the Pasig River Urban Development (IAC-PRUD), said this is one of the reasons the project is not only for beautification.

The revitalization project aims to capitalize on the full potential of the Pasig River and bring it to the level of other major waterways such as the Thames River in London, the Chao Phraya in Bangkok and the Seine River in Paris.

Acuzar said notable among these waterways, aside from being popular tourist attractions, are the commercial and mixed-use developments that surround it.

With the successful revitalization of the Pasig River, commuters can transition from surface roads to water transport through the project through bridge walks.

These will be constructed at major points serving as pickup and drop-off points for the water ferries. (See: https://businessmirror.com.ph/2024/02/05/pasig-river-revitalization-seen-to-offer-alternative-transport/).

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Experts share remarkable effects of removing restrictive dams from river: 'A case study in how we can improve habitat'

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Understanding rivers and their social relations: A critical step to advance environmental water management

Sue Jackson

Rebecca E. Tharme

Michael Douglas

Joseph E. Flotemersch

Margreet Zwarteveen

Chicu Lokgariwar

Mariana Montoya

Gail T. Tipa

Timothy D. Jardine

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Barbara Cosens

Chris Dickens

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Dirk J. Roux

Albert Ruhi

Angela H. Arthington

1 |. INTRODUCTION

THE BRISBANE DECLARATION AND GLOBAL ACTION AGENDA ON ENVIRONMENTAL FLOWS (2018)

2 |. HOW HAS ENVIRONMENTAL FLOW SCIENCE HISTORICALLY CONCEIVED OF RIVER-HUMAN INTERACTIONS?

3 |. CASE STUDIES: A DIVERSITY OF RELATIONSHIPS BETWEEN HUMANS AND RIVER FLOWS

3.1 |. The Patuca River, Honduras

3.2 |. The Ganga River, India

3.3 |. The Athabasca River, Canada

3.4 |. Murray-Darling Basin, Australia

3.5 |. Kakaunui and Orari rivers, New Zealand

4 |. DISCUSSION