Physical Habitat Simulation Model Research Articles

Ecological Flows Assessment of Significant Fish Species in Iril River, Northeast India Through PHABSIM

Background: Freshwater fishes are facing alarming threats due to various anthropogenic activities. The present study estimates the ecological flow requirements for Bangana dero and Wallago attu fish species in the Iril River through a habitat modeling approach. Methods: The habitat suitability modeling of the target species was carried out using the physical habitat simulation model (PHABSIM). PHABSIM model was developed for the river stretch extending about 6,000 m in Iril River. 11 cross-sections at a distance of about 500 m were specified in the model. In the model, habtae was set to run and weighted usable area (WUA) was obtained as output from the habitat model. Result: The highest WUA for the two fish species is estimated at 21 cumecs of discharge. The mean flow of the Iril River is about 27.7 cumecs, which is 6.7 cumecs higher than the optimal ecological flow requirements. The estimation of ecological flow requirements is required to have a better understanding of Weighted Usable Area (WUA) for planning and management strategies. This information may enable stakeholders to develop ameliorative strategies and adopt meaningful measures suitable for the conservation of significant fish species.

An algorithm to generate 2D bathymetry of an Alpine river for habitat suitability assessment.

Here we present an original approach to generate 2D high detail riverbed based on a drone photogrammetric survey, and RTK bathymetry measurements for Mera river in the Italian Alps. The aim is to better represent macro-roughness and riverbed structure of the river, also extending it to an ungauged area. Specifically, we apply a step-by-step approach. I) Depth and average slope of the riverbed were calculated from bathymetry data. II) Thus, a trapezoidal channel with constant slope and variable width was defined using the drone images. III) Riffle-pool sequence was assessed as a function of river width and applied to the generated channel. IV) Finally, the semi-random Perlin Noise was added to recreate riverbed irregularities in the natural stream. HEC-RAS 2D hydraulic software was then implemented to assess spatialized water depth and velocity. The proposed methodology could be quite relevant in river hydraulics to decouple roughness coefficient from water submergence, and in Physical Habitat Simulation Model (PHABSIM), where the dependency of the output is not linear with hydraulic parameters (i.e. water depth and velocity). Indeed, we apply PHABSIM for a case study of a stretch of the river and results are compared with a previous environmental study for Mera river.

Can the regulation of Golden Inland Waterways meet the needs of navigation, flood control, and ecology? A model-based case study

In recent years, the ecological functions of inland waterways have received much attention. Roughness elements have been used in waterway regulations (WRs) to guard the riverbed and improve physical habitat. However, the response of aquatic organisms to regulations varies widely. It is controversial whether inland waterway regulations can achieve the sustainable function of navigation, flood control and ecological needs.This paper evaluated the influence of WRs on aquatic habitat by using the physical habitat simulation models combining a 2D hydrodynamic model and habitat models. Compared with a reference model with no-engineering, the habitat suitability of zoobenthos, four major species of Chinese carp's spawning ground and the Yangtze finless porpoise at different flow discharges were simulated under different densities of river training structures and types of roughness elements. Results showed that the implementation of the WRs can adjust the distribution of the suitability of aquatic habitats, but does not change the pattern of suitability with discharge. The response of biological habitats to regulation projects varied by species. Regulation can maintain the stable habitat during dry and flood periods, reducing the effect of extreme weather on aquatic organisms. Roughness elements are not suitable for large-scale use in WRs. The “win-win” agreement between economic and ecological issues can be obtained through pre-optimization.

Calculation and evaluation of suitable ecological flows for eco-environmental recovery of cascade-developed rivers

River cascade development affects the hydrological and habitat characteristics of the region and disrupts the dynamic balance of stable river ecosystems. The most profound impact of river cascade development is on the resident fish species. River ecosystem restoration for maximum river habitat improvement is generally based on water security and environment improvement and effectively embodies the nature-based solutions (NbS) concept of naturalized restoration. Yuanjiang (Y.J.) River is an international river in southwest China seriously affected by cascade development. By determining the response of the river ecosystem and using the key performance indicator method, Yuanjiang carp (Cyprinus carpio rubrofuscus) and red giant catfish (Bagarius rutilus) were identified as the key species in the main stream of the Y.J. River., and the ecological effects of river cascade development on them were studied by applying two-dimensional hydrodynamic physical habitat simulation and multi-objective ecological scheduling models. Based on the calculation results for ecological operation optimization of cascade reservoirs, an improved progressive optimality algorithm was used to calculate the ecological flows required to maintain the stability of the river ecosystem. With the increasing extent of cascade development in the river, important indicators, such as the intra-annual, extreme, high, and low flows have changed significantly, and the hydrological characteristics of the main stream have changed rapidly and comprehensively. Habitat suitability curves were used to determine the appropriate water depth and delineate the weighted usable area required for the spawning, nursing, and growing periods of the key fish species. The suitable ecological flows required for the three life-cycle stages of the C. carpio rubrofuscus accounted for 34, 45, and 62 %, respectively, of the multi-year mean natural water inflow at the Qiaotou (Q.T.) cascade, whereas those required for the three respective periods of B. rutilus accounted for 47, 98, and 27 %, respectively, of the multi-year mean natural water inflow at the Madushan (M.D·S.) cascade. Considering the physiological lifecycle demands of the indicator/key fish species and the upper limit of water resources development and utilization in the key river section, the ecological flow precipitation frequency in the Q.T.-Luodie (Q.T.-L.D.) and M.D·S.-Xinjie (M.D·S.-X.J.) sections (currently at 25, 50, and 75 %, respectively) can be increased to 100 % under optimal operating conditions (cascade hydropower station optimal operation). After implementing the multi-objective ecological operation at the Y.J. River main-stream cascade reservoirs, the suitable habitat area for C. carpio rubrofuscus and B. rutilus increased significantly (>10 % and 15 %, respectively). In general, the NbS-based ecological flow calculation method for cascade-developed rivers has a wide range of applications, which can be useful for the eco-environment restoration of rivers and improving the living habitats of waterway organisms.

Suitability Assessment of Fish Habitat in a Data-Scarce River

Assessing fish habitat suitability in a data-scarce tidal river is often challenging due to the absence of continuous water quantity and quality records. This study is comprised of an intensive field study on a 42 km reach which recorded bathymetry and physical water quality parameters (pH, electroconductivity, dissolved oxygen, and total dissolved solids) testing and corresponding water levels and velocity. Frequent water sampling was carried out on 17 out of 90 locations for laboratory water quality tests. Based on this, an interpolation technique, i.e., Inverse Distance Weighted (IDW), generates a map in a Geographic Information System (GIS) environment using ArcGIS software to determine the river water quality parameters. Additionally, a hydrodynamic model study was conducted to simulate hydraulic parameters using Delft3D software followed by a water quality distribution. During validation, the Delft3D-simulated water quality could reasonably mimic most field data, and GIS featured dissolved oxygen. The overall water quality distribution showed a lower dissolved oxygen level (~3 mg/L) in the industrial zone compared to the other two zones during the study period. On the other hand, these validated hydraulic properties were applied in the Physical Habitat Simulation Model (PHABSIM) set up to conduct the hydraulic habitat suitability for Labeo rohita (Rohu fish). Thus, the validated model could represent the details of habitat suitability in the studied river for future decision support systems, and this study envisaged applying it to other similar rivers.

Assessment of Environmental Flow Requirements for Four Major Chinese Carps in the Lower Reaches of the Jinsha River, Southwest China

An appropriate environmental flow (AEF) is one of the necessary conditions for fish spawning. The operation of cascade reservoirs in the lower reaches of the Jinsha River has changed the discharge process downstream, which in turn has directly affected the spawning habitat of fishes. Determining how to quantitatively evaluate the impact of different outflows from Xiangjiaba Reservoir on the spawning habitat of four major Chinese carp species in the downstream area is a key problem that must be solved immediately. The Yibin River section was selected as the study area, and the velocity and water depth were measured. A physical habitat simulation model (PHABSIM) was used to analyze the main hydrodynamic conditions that affect the spawning of the four major Chinese carp species and to quantify the weighted usable area (WUA) for the fishes based on different outflows from Xiangjiaba Reservoir. Hydrodynamic suitability curves for the four major Chinese carp species were established based on observed data from 2012 to 2020, and a two-dimensional hydrodynamic model was developed using a triangular grid to obtain the hydrodynamic distribution characteristics of the fish habitat. Then, the AEF range was obtained based on the outflow-WUA relationship. The results showed that the velocity during the spawning period was 0.6–1.3 m/s, the most appropriate velocity was 0.9–1.0 m/s, the water depth range was 3.0–18.0 m, and the most appropriate water depth was 9.0–12.0 m. Additionally, the AEF range was 2,000–4,500 m3/s, and the optimal AEF was, m3/s. The research results provide a scientific basis for the ecological operation of cascade reservoirs in the lower reaches of the Jinsha River.

Operation chart optimization of multi-hydropower system incorporating the long- and short-term fish habitat requirements

There are increasing calls to incorporate ecological requirements into hydropower operation, however it remains a challenge to balance average ecological benefit over a long period of time and ecological damage under wet/dry conditions. This study proposes a new hydropower-ecological operation chart of cascade hydropower stations in which limited ecological curves were introduced and all guiding curves were optimized, aiming to improve the long-term average fish habitat quality and to mitigate the negative impacts caused by drought/flood events on fish habitat without reducing power generation compared to the conventional reservoir operation. The JiaSA(JSA)-MaduShan (MS) cascaded reservoirs in Yuan Basin were chosen as the research area. The physical habitat simulation model (PHABSIM) is used to quantify the hydrological requirements of the target fish species at different life stages. At an ecological need fitness target of 70%, under the guidance of hydropower-ecological operation chart, without reducing the power generation, the average ecological need fitness at the downstream of JSA and MS hydropower stations is increased by 0.09% and 1.06%, the frequency of ecological damage is reduced by 6.12% and 25.00%, and the ecological damage degree during wet/dry periods is reduced by 1.96% and 0.52%, respectively. However, when ecological need fitness target is higher than 80%, the frequency and magnitude of ecological damage are significantly increased. Therefore, the proposed operation chart has the potential to increase the multi-objective benefits of hydropower system and can be easily applied to other cascaded reservoirs in different basins.

Assessment of environmental water requirement for rivers of the Miankaleh wetland drainage basin

The Miankaleh wetland, one of the richest ecosystems in the north of Iran, has experienced an unprecedented environmental degradation caused by overexploitation of the water resources and climatic changes in recent years. This research aims to estimate the environmental water requirement (EWR) for the rivers that drain into the wetland. For this purpose, comprehensive data were collected through physiographic, climatic, hydrologic, ecologic, and field studies of the wetland and its drainage basin. To estimate the EWR, we applied several methods including the Tenant, the Eco-deficit, the flow duration curve, the Wetted-Perimeter method, and the physical habitat simulation model (PHABSIM) and the results were evaluated based on the natural discharge of the rivers before retrogression of the Miankaleh wetland. Further, the results showed that the consideration should be given to the Wetted-Perimeter and the PHABSIM Model for estimation of the EWR for the rivers of the Miankaleh wetland given the seasonality of the rivers and hydroclimatic condition of the study area. The mean annual EWR of the rivers was estimated between 0.12 and 2.03 m3/s, which is close to the values of the bank full flows. The current discharge of the rivers are less than the estimated EWR, showing the discharge rates do not meet the water requirement for aquatic species of the Miankaleh wetland

Bioenergetic Habitat Suitability Curves for Instream Flow Modeling: Introducing User‐Friendly Software and its Potential Applications

Habitat suitability curves (HSCs) are the biological component of habitat simulation tools used to evaluate instream flow management trade‐offs (e.g., the physical habitat simulation model). However, traditional HSCs based on empirical observations of habitat use relative to availability have been criticized for generating biased estimates of flow requirements and for being poorly transferable across locations. For fish like salmonids that feed on drifting invertebrates, bioenergetics‐based foraging models that relate habitat conditions to net energy gain offer an alternative approach that addresses some of these shortcomings. To make this technique more accessible for practitioners, we present free and user‐friendly software for generating bioenergetics‐based HSCs. The software also allows sensitivity analyses of HSCs to factors like fish size or prey abundance as well as direct integration of hydraulic data. While some caveats remain, bioenergetic HSCs should offer a more rigorous and credible means for quantifying habitat suitability for instream flow modeling.

Effects of land use changes on the ecological operation of the Panjiakou-Daheiting Reservoir system, China

The problem of insufficient water for ecological purposes in the Luanhe River basin requires urgent resolution. The regional hydrological cycle is affected by the Panjiakou-Daheiting Reservoir system and by changes in land use in the upper watershed. Therefore, this system was selected as a study area to simulate ecological reservoir operation and analyze the effects of changes in land use on ecological operation. A physical habitat simulation model (PHABSIM) was built to determine the minimum and suitable ecological water demand. Then, an ecological reservoir operation model using an improved differential evolution (DE) algorithm was established. Simulated inflow data under the land use conditions in 1970 and 2015 were input into the model, and the effects of changes in land use on ecological operation and on the weighted usable area (WUA) for cyprinoids were calculated. The results show that ecological reservoir operation significantly improves the ecological water supply and increases cyprinoid habitat. The changes in land use led to a decrease in annual runoff, which further reduced the urban water supply by 0.67%–2.25% and the ecological water supply by 0.45%–2.04% at different flow frequencies. The land use changes also caused the WUA to decrease by 1746–2999 m2/km at different flow frequencies, with a decrease rate of 1.04%–6.28%. This study could provide valuable information for water resource managers operating reservoirs in river ecosystems and planning to cope with water shortages caused by land use change in water-deficient areas.

Study on the Ecological Operation and Watershed Management of Urban Rivers in Northern China

Small- and medium-sized rivers are facing a serious degradation of ecological function in water resource-scarce regions of Northern China. Reservoir ecological operation can restore the damaged river ecological environment. Research on reservoir ecological operation and watershed management of urban rivers is limited in cold regions of middle and high latitudes. In this paper, the urban section of the Yitong River was selected as the research object in Changchun, Northern China. The total ecological water demand and reservoir operation water (79.35 × 106 m3 and 15.52 × 106 m3, respectively) were calculated by the ecological water demand method, and a reservoir operation scheme was established to restore the ecological function of the urban section of the river. To examine the scientific basis and rationality of the operation scheme, the water quality of the river and physical habitat after carrying out the scheme were simulated by the MIKE 11 one-dimensional hydrodynamic-water quality model and the Physical Habitat Simulation Model (PHABSIM). The results indicate that the implementation of the operation scheme can improve the ecological environment of the urban section of the Yitong River. A reform scheme was proposed for the management of the Yitong River Basin based on the problems in the process of carrying out the operation schemes, including clarifying department responsibility, improving laws and regulations, strengthening service management, and enhancing public participation.

Exploitation of Velocity Gradients by Sympatric Stream Salmonids: Basic Insights and Implications for Instream Flow Management

AbstractHydraulic heterogeneity can strongly influence habitat selection by stream fishes. Velocity gradients created by channel roughness and flow obstructions may be particularly important for species that feed on drifting invertebrates, where maintaining focal points in low‐velocity microhabitats adjacent to faster water allows fish to scan a larger water volume for prey while minimizing swimming costs. However, these velocity gradients are rarely integrated into habitat suitability criteria used for defining instream flow requirements, which are generally based on mean column velocity measurements at the focal point location. It is also unclear how velocity gradient exploitation differs among sympatric drift‐feeding species. We measured the use of velocity gradients by two sympatric juvenile salmonids, Coho Salmon Oncorhynchus kisutch and steelhead O. mykiss, in a midorder cobble–boulder‐dominated river. We compared focal point velocities of fish to adjacent velocities within their foraging area and compared the magnitude of velocity and kinetic energy gradients between species. We then explored how lateral velocity gradients may bias instream flow assessments by deriving two sets of velocity habitat suitability curves (HSCs): conventional HSCs using average water column velocities measured at focal point locations and spatially averaged HSCs incorporating adjacent velocities (four body lengths from focal points). These contrasting HSCs were then used as input into the physical habitat simulation model to predict the influence of flow on habitat availability. Both species often used focal velocities that were lower than adjacent points, but the magnitude of these velocity gradients was higher for steelhead, consistent with known differences in foraging behavior, habitat selection, and physiology. Incorporating adjacent velocities into HSCs resulted in a ~40% (steelhead) and ~10% (Coho Salmon) increase in flows predicted to optimize habitat availability. Thus, small‐scale heterogeneity in velocity used by drift‐feeding fish can lead to large biases in flow assessments.

Incorporation of Optimal Limited Ecological Curves into the Operation Chart of Cascade Hydropower Systems to Alleviate Ecological Damages in Hydrological Extremes

Most ecological operation charts of hydropower stations have focused on the average ecological benefits over a long period of time, while the possible ecological damage caused by flood or drought is often overlooked or averaged out. This study proposed a new hydropower-ecological operation chart of cascade hydropower stations, in which limited ecological curves were introduced and optimized to alleviate the negative impacts caused by drought or flood events on fish habitat and to maintain the long-term average habitat quality without reducing the power generation. The optimal ecological discharge range at a given ecological conservation target was determined from the weighted usable area-discharge curve using the physical habitat simulation model, and then the upper and lower limited ecological curves were obtained by reverse calculation, which together with the conventional operation chart (COC) formed the ecological operation chart (EOC). The limited ecological curves were further optimized with the goal of reducing the ecological damage frequency in wet and dry extremes, and then incorporated into COC to form the optimized ecological operation chart (OEOC). A case study was performed with Jasajiang (JS) and Madushan (MDS) cascade reservoirs on the Yuan River in southwestern China. The results show that the EOC that takes into account the ecological benefits can reduce the ecological damage frequency compared to the COC, but potentially at the expense of the overall ecological benefit. However, further optimization of limited ecological curves in OEOC makes it possible to obtain higher short-term ecological benefit and lower ecological damage frequency with the loss of lower overall ecological benefit. Specifically, OEOC is helpful to reduce the ecological damage frequency and improve the power generation and overall ecological benefit at an ecological target of 60 ~ 80%. Notably, at an ecological target of 80%, OEOC results in a 4.1% increase in power generation and a 11.25% decrease in ecological damage frequency for JS-MDS cascade reservoirs compared with that of COC, respectively.

Indigenous Rights and Climate Change: The Influence of Climate Change on the Quantification of Reserved Instream Water Rights for American Indian Tribes

The people indigenous to the Western portion of the lands now referred to as North America have relied on aquatic species for physical, cultural, and spiritual sustenance for millenia. Such indigenous peoples, referred to in the American legal system as Indian tribes, are entitled to water rights for fish habitat pursuant to the Winters Doctrine, which holds that the federal government impliedly reserved water rights for tribes when reservations were created. Recently, the methodology for quantifying these rights has been the Instream Flow Incremental Methodology (IFIM) and/or one of its major components, the Physical Habitat Simulation Model (PHABSIM). These models result in water right claims for fixed quantities of water, which—although not required by law—result in instream water rights that are decreed without any means for adjustment to account for changing conditions. Ultimately, climate change will likely alter the amount of water necessary to protect aquatic habitat, rendering obsolete any water right that is based on a fixed quantity. As climate change continues to worsen, we argue that quantifying reserved water rights for inflexible fixed quantities imposes an unreasonable burden on American Indian tribes. Instead, we suggest the application of a number of integrated technical and legal solutions to mitigate the uncertainty Indian tribes currently face from climate change as they seek to protect their rights, resources, and homelands.

Law and Science Series No. 1: The Contemporary Methodology for Claiming Reserved Instream Flow Water Rights to Support Aquatic Habitat

This article is the first in a series to provide information related to commonly used technical methodologies in furtherance of legal rights held by American Indian Tribes. Specifically, this article discusses the method for estimating water rights necessary to protect instream habitat to support fish. Unlike reserved water rights for irrigation — which has the well settled practicably irrigable acreage (“PIA”) standard — the United States Supreme Court has not identified a single quantification methodology appropriate for traditional uses of water. Instead, lower courts have fashioned a more ad hoc approach to quantifying traditional reserved water rights. This seems preferable given that unlike irrigation water rights, which are fairly uniform in their nature, each tribe’s traditional uses of water are unique and driven by the physical, historical, and cultural factors present for each tribe. Although the method for quantifying these rights have evolved over time, courts have slowly converged on the Instream Flow Incremental Methodology (IFIM) and its component part, the Physical Habitat Simulation Model (“PHABSIM”). Although the IFIM/PHABSIM method does not enjoy the de jure recognition of its sister-methodology PIA, the consistent use and acceptance of this method have caused it to become the de facto method for quantifying reserved instream water rights to protect fish habitat. The purpose of this article is to provide an explanation of the IFIM/PHABSIM methodology in an effort to put practitioners in the position to apply and, where necessary, critique the method. It proceeds in a chronological fashion; describing from beginning to end the steps necessary to develop a reserved instream water right claim using the IFIM/PHABSIM method.

Effects of damming and climatic change on the eco-hydrological system: A case study in the Yalong River, southwest China

Abstract The eco-hydrological system in China is undergoing dramatic changes in recent decades due to climate change and construction of cascade dams for power production. Given that multiple drivers often interact in complex and nonadditive ways, the purpose of this study is to predict future changes in runoff and fish habitat quality of the Yalong River basin attributed to the individual and combined effects of cascade dam construction and climate change. The bias corrected and spatially downscaled CMIP5 GCM projections are used to drive the Soil and Water Assessment Tool hydrological model and to simulate and predict runoff responses under diverse scenarios. The physical habitat simulation model is established to describe the relationship between river hydrology and fish habitat quality and to assess the individual and combined effects of cascade dam construction and climate change. The mean annual temperature and precipitation of the Yalong River in 2020–2100 are predicted to increase at a rate of 0.016–0.487 °C/10a and 4.55–10.13 mm/10a, with an increase of 1.63–3.25 °C and 0.66–3.34% in comparison with those in 1957–2012, respectively. While, the mean annual runoff of the middle and lower reaches is increased by 11.77%–16.63% and 14.02%–19.02% compared with that in the history, respectively. The construction of cascade dams could significantly improve the fish habitat quality of the Yalong River basin, especially in dry seasons, and consequently the ecological conservation degree is increased by about 2%. In the middle reaches, changes in runoff from February to October are mainly determined by cascade dam construction, but the effect of climate change becomes more pronounced from November to January. Similarly, cascade dam construction has a more significant effect on runoff of the lower reaches than climate change except in November and December.

A novel operation chart for cascade hydropower system to alleviate ecological degradation in hydrological extremes

Incorporating limited ecological curves, a novel operation chart optimization method is proposed for the multipurpose hydropower systems, which is capable of improving power generation and overall ecological condition and alleviating ecological degradation under extreme dry or wet conditions. The method mainly includes: (1) determine the optimal ecological discharge using weighted usable area-discharge curve based on the physical habitat simulation model (PHABSIM); and (2) establish the operation chart optimization model aiming to maximizing power generation and overall ecological condition and solve the model with DPSA; then (3) derive the limited ecological curves and incorporate them in the operation chart. A case study is performed with Jasajiang (JS) and Madushan (MDS) reservoirs on the Yuan River in southwestern China. The results show that the optimized operation charts result in a 1.72% and 5.99% increase in hydropower generation and a 0.27% and 1.13% increase in ecological conservation degree for MDS reservoir, respectively. In addition, the frequency of ecological damage is reduced from 6.11% to 1.11% for JS reservoir and from 26.67% to 3.89% for JS and MDS reservoirs, respectively. A further discussion using a time series of random runoff generated by first-order Markov model has confirmed the adaptability of this operation chart. The feasibility and potential applications of this operation chart has been confirmed.

Future changes in Yuan River ecohydrology: Individual and cumulative impacts of climates change and cascade hydropower development on runoff and aquatic habitat quality

The eco-hydrological system in southwestern China is undergoing great changes in recent decades owing to climate change and extensive cascading hydropower exploitation. With a growing recognition that multiple drivers often interact in complex and nonadditive ways, the purpose of this study is to predict the potential future changes in streamflow and fish habitat quality in the Yuan River and quantify the individual and cumulative effect of cascade damming and climate change. The bias corrected and spatial downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) General Circulation Model (GCM) projections are employed to drive the Soil and Water Assessment Tool (SWAT) hydrological model and to simulate and predict runoff responses under diverse scenarios. Physical habitat simulation model is established to quantify the relationship between river hydrology and fish habitat, and the relative change rate is used to assess the individual and combined effects of cascade damming and climate change. Mean annual temperature, precipitation and runoff in 2015–2100 show an increasing trend compared with that in 1951–2010, with a particularly pronounced difference between dry and wet years. The ecological habitat quality is improved under cascade hydropower development since that ecological requirement has been incorporated in the reservoir operation policy. As for middle reach, the runoff change from January to August is determined mainly by damming, and climate change influence becomes more pronounced in dry seasons from September to December. Cascade development has an effect on runoff of lower reach only in dry seasons due to the limited regulation capacity of reservoirs, and climate changes have an effect on runoff in wet seasons. Climate changes have a less significant effect on fish habitat quality in middle reach than damming, but a more significant effect in lower reach. In addition, the effect of climate changes on fish habitat quality in lower reach is high in dry seasons but low in flood seasons.

Ecological Flow Requirement for Fishes of Godavari River:Flow Estimation Using the PHABSIM Method

Fish habitat requirements are an essential aspect of the estimation of environmental flows. In India, a few studies have proposed environmental flows for the major rivers on the basis of qualitative observation or expert opinion. As part of a study regarding the effect of altered flow across the Godavari river on fishes, we estimated flow requirement of the fishes using a physical habitat simulation model (PHABSIM). This model uses habitat requirement of selected fish species in the form of habitat suitability curves (HSCs) against river habitat availability. We developed HSCs for five economically important fishes ( Bangana dero, Cirrhinus cirrhosus, Labeo calbasu, Labeo fimbriatus and Wallago attu ). These HSCs indicate that B. dero prefers high velocities (0.9–1.2 m/s) compared with the other species and that L. fimbriatus prefers deeper areas (1.2–1.5 m). C. cirrhosus uses low flows with moderate depth (0.3–0.6 m/s; 0.6–1.5 m). The HSCs were used in PHABSIM along with instream habitat data recorded from four cross-sections to predict the weighted usable areas (WUAs) of the fishes. The relationship between habitat area and discharge was used to predict the minimum acceptable flow for maintaining fish habitats. On the basis of the WUA–discharge relationship curve, 26% of the mean flow was recommended as the minimum ecological flow required below the Polavaram dam of Godavari river.

Developing flow–ecology relationships: Implications of nonlinear biological responses for water management

Abstract Empirical relationships between stream flow and ecological responses (flow–ecology relationships) are essential for establishing environmental flows and evaluating tradeoffs between instream values and out‐of‐stream uses. Establishing the shape of flow–ecology relationships (i.e. slope, linearity versus nonlinearity) is particularly important to avoid crossing ecological thresholds in water management. This review focuses on ecological responses to discharge at low summer flows when out‐of‐stream water demand is often highest, and identifying ecological contexts where nonlinearities are most likely. Most physical attributes (temperature, dissolved oxygen, available habitat) and ecological responses (energy flow, fish survival, recruitment, community structure) show at least some evidence of nonlinear relationships with flow, although assumptions of linearity may be reasonable across limited discharge ranges which may include low flows. Nonlinearities are most likely in systems that are near existing thresholds (e.g. cold‐water transitional fish communities that are close to upper thermal tolerances). The probability of nonlinearities is likely to increase under future landuse and climate change scenarios, particularly in combination with other stressors, such as eutrophication, which may greatly accelerate temperature‐related decline in dissolved oxygen under climate warming. Managers need to anticipate changes in flow–ecology relationships and develop management systems that are robust to change. Field programmes to establish the slope and linearity of local flow–ecology relationships are essential for regional management, but developing generalisable flow–ecology relationships that are transferrable to regions with limited resources also needs to be a priority. Generalised relationships can be generated through meta‐analysis of empirical flow–ecology relationships, and may prove especially useful if they can capture how environmental and ecological context (channel size and morphology, landuse, flow regime, antecedent conditions, habitat or taxonomic guild) affect flow–ecology relationships. For instance, linking empirical data from flow–ecology relationships to available habitat predicted by physical habitat simulation models (e.g. PHABSIM) may provide a better mechanistic basis for modelling ecological responses, while providing much needed validation for habitat simulation approaches. This would also help bridge the gap between emerging holistic environmental flow modelling approaches and more traditional habitat simulation methods.