ASSESSING THE CUMULATIVE IMPACTS OF HYDROPOWER REGULATION ON THE FLOW CHARACTERISTICS OF A LARGE ATLANTIC SALMON RIVER SYSTEM

We assessed the influence of hydropower on the flow characteristics of the river Tay, one of the UK's most heavily regulated catchments and important Atlantic salmon fisheries. Hydropower developments in the mid‐20th century preceded flow data collection, resulting in knowledge gaps over how far regulated flows deviate from natural and how ecosystem functioning might have been impacted. We used 29 unregulated catchments in and around the Tay to assess the relationships between hydroclimatic conditions, landscape structure and the overall flow regime, as well as the annual, monthly and daily flow metrics. This allowed the identification of flow characteristics by using an integrated suite of regression approaches (nonlinear, MLR and random forests) to assess likely impacts at 11 regulated sites. The results showed that the impacts of regulation are highly variable in both space and time. Headwater sub‐catchments are most heavily affected, and water imports or exports as part of hydropower schemes can increase or decrease annual runoff by up to 50%, respectively. On a monthly basis, regulation primarily increased summer low flows; winter high flows increased in catchments affected by water imports and reduced where there was a net water export. At larger catchment scales, impacts were relatively small, as unregulated tributaries re‐naturalize the flows and the effects of intra‐basin transfers balance. Non‐stationarity in climate and water use in the catchment dictates that adaptive management of flows may be necessary to protect ecosystems services. Copyright © 2013 John Wiley & Sons, Ltd.     

Response by fish assemblages to an environmental flow release in a temperate coastal Australian river: A paired catchment analysis

Defining appropriate environmental flow regimes and criteria for the use of environmental water allocations requires experimental data on the ecological impacts of flow regime change and responses to environmental water allocation. Fish assemblages in one regulated and one unregulated tributary paired in each of two sub‐catchments of the Hunter River, coastal New South Wales, Australia, were sampled monthly between August 2006 and June 2007. It was predicted that altered flow regime due to flow regulation would reduce species richness and abundance of native fish, and assemblage composition would differ between paired regulated and unregulated tributaries. Despite significant changes in richness, abundance and assemblage composition through time, differences between regulated and unregulated tributaries were not consistent. In February 2007, an environmental flow release (‘artificial flood’) of 1400 ML was experimentally released down the regulated tributary of one of the two catchments over 6 days. The flow release resulted in no significant changes in fish species abundances or assemblage composition when compared to nearby unregulated and regulated tributaries. Flow regulation in this region has reduced flow variability and eliminated natural low‐flow periods, although large floods occurred at similar frequencies between regulated–unregulated tributaries prior to and during 2006–2007, resulting in only moderate changes to regulated flow regimes. Barriers to dispersal within catchments also compound the effects of flow regulation, and findings from this study indicate that the location of migratory barriers potentially confounded detection of the effects of flow regime change. Further experimental comparisons of fish assemblages in regulated rivers will refine river‐specific response thresholds to flow regime change and facilitate the sustainable use of water in coastal rivers. Copyright © 2010 John Wiley & Sons, Ltd.     

Combined Effects of Reservoir Operations and Climate Warming on the Flow Regime of Hydropower Bypass Reaches of California's Sierra Nevada

Alterations to flow regimes from regulation and climatic change both affect the biophysical functioning of rivers over long time periods and large spatial areas. Historically, however, the effects of these flow alteration drivers have been studied separately. In this study, results from unregulated and regulated river management models were assessed to understand how flow regime alterations from river regulation differ under future climate conditions in the Sierra Nevada of California, USA. Four representative flow alteration metrics—mean annual flow, low flow duration, centroid timing and mean weekly rate of decrease—were calculated and statistically characterized under historical and future unregulated and regulated conditions over a 20‐year period at each of the eight regulated river locations below dams across the Sierra Nevada. Future climatic conditions were represented by assuming an increase in air temperature of 6 °C above historical (1981–2000) air temperatures, with no change in other meteorological conditions. Results indicate that climate warming will measurably alter some aspects of the flow regime. By comparison, however, river regulation with business‐as‐usual operations will alter flow regimes much more than climate warming. Existing reservoirs can possibly be used to dampen the anticipated effects of climate warming through improved operations, though additional research is needed to identify the full suite of such possibilities. Copyright © 2014 John Wiley & Sons, Ltd.     

Understanding the Thermal Regime of Rivers Influenced by Small and Medium Size Dams in Eastern Canada

Although small and medium‐size dams are prevalent in North America, few studies have described their year‐round impacts on the thermal regime of rivers. The objective of this study was to quantify the impacts of two types of dams (run‐of‐river, storage with shallow reservoirs) on the thermal regime of rivers in eastern Canada. Thermal impacts of dams were assessed (i) for the open water period by evaluating their influence on the annual cycle in daily mean water temperature and residual variability and (ii) for the ice‐covered winter period by evaluating their influence on water temperature duration curves. Overall, results showed that the run‐of‐river dam (with limited storage capacity) did not have a significant effect on the thermal regime of the regulated river. At the two rivers regulated by storage dams with shallow reservoirs (mean depth < 6 m), the annual cycle in daily mean water temperature was significantly modified which led to warmer water temperatures in summer and autumn. From August to October, the monthly mean water temperature at rivers regulated by storage dams was 1.4 to 3.9°C warmer than at their respective reference sites. During the open water period, the two storage dams also reduced water temperature variability at a daily timescale while increased variability was observed in regulated rivers during the winter. Storage dams also had a warming effect during the winter and the winter median water temperature ranged between 1.0 and 2.1°C downstream of the two storage dams whereas water temperature remained stable and close to 0°C in unregulated rivers. The biological implications of the altered thermal regimes at rivers regulated by storage dams are discussed, in particular for salmonids. Copyright © 2016 John Wiley & Sons, Ltd.     

MULTISTAGE ANALYSIS OF HYDROLOGIC ALTERATIONS IN THE YELLOW RIVER,CHINA

Natural river flow regimes provide an array of ecological and social functions by sustaining the health of riverine ecosystems. To identify the hydrologic alterations in the lower Yellow River basin caused by natural factors and human activities, we developed multistage hydrologic analysis to investigate the temporal variability of the river's flow regimes. We used a cumulative departure curve and Mann–Whitney–Pettitt nonparametric tests to determine possible change points based on hydrologic data from 1950 to 2006. We then used the range of variability approach to characterize and to quantify the temporal variability of the hydrologic regimes that were associated with perturbations such as dam operation, flow diversions or intensive conversion of land use within the watershed. In the case study, three stages in hydrologic alterations of the flow regime were found: a stage without human impacts, a stage with excessive human impacts and a reservoir‐regulation stage. Our results indicated that (i) after 1997, dam operation efficiently achieved flood control using sediment regulation activities; (ii) although effective in flood control, the Xiaolangdi Reservoir could not handle situations with extremely low flow, such as during droughts; and (iii) under the arid climate of the Yellow River basin, water consumption by agriculture was the main cause of water shortages. The current study shows that multistage hydrologic analysis can greatly assist regional water resources management and the restoration of riparian eco‐environmental systems affected by dam construction under a changing environment. Copyright © 2012 John Wiley & Sons, Ltd.     

The effects of flow regulation and climatic variability on obstructed drainage and reverse flow contribution in a Northern river–lake–Delta complex,Mackenzie basin headwaters

A distinctive hydrological feature of the Lake Athabasca–Peace–Athabasca Delta (LA‐PAD) complex is that flow in channels that drain the system reverses direction when stage on the Peace River exceeds that for the central lakes. This river's hydrology has experienced natural and human induced changes since 1968. This study investigates the importance of spring break‐up and open‐water induced outflow obstruction and reverse flow contributions to annual lake level maxima under natural (1960–1967), regulated (1976–2004) and naturalized (1976–1996) flow regimes. Obstructed and reverse flow events during spring break‐up were common prior to and following flow regulation, suggesting that natural climatic variability in source areas below the W.A.C. Bennett Dam exerted a strong influence on their occurrence. Antecedent hydrological conditions, such as fall freeze‐up lake level, break‐up magnitude, peak spring flow and initial open‐water lake level were significantly associated with annual lake level maxima. During the summer period, lake level was linked to sustained high flows on the Peace River. The river obstructed outflow and contributed reverse flow to the LA‐PAD in each year prior to 1968. Following regulation, however, more than half the years did not experience any open‐water obstruction and/or reversal, and those that did were characterized by smaller events. The average estimated duration of obstruction was more than two weeks shorter and reverse flow volume was reduced by ～90% under a regulated regime compared to a simulated naturalized flow regime. This implied a lowered potential for lateral lake expansion into the delta floodplain in some years. The regulated hydrology could produce large stormflow and high lake levels, but only under extreme climatic events in areas below the dam and/or human‐induced alterations to normal reservoir operation. Copyright © 2009 Crown in the right of Canada and John Wiley & Sons, Ltd.     

Growth,Condition and Survival of Three Forage Fish Species Exposed to Two Different Experimental Hydropeaking Regimes in a Regulated River

Hydroelectric dam operation can alter discharge and temperature patterns, impacting fish populations downstream. Previous investigations into the effects of river regulation on fish have focused on a single species within a river, yet different results among studies suggest the potential for species‐specific impacts. Here, we compare the impacts of two different hydropeaking regimes relative to a naturally flowing river on three ecologically important members of the forage fish community: longnose dace (Rhinichthys cataractae), slimy sculpin (Cottus cognatus) and trout‐perch (Percopsis omiscomaycus). Annual growth, estimated from otolith back‐calculations, was higher for each of the species in the regulated river relative to the naturally flowing river but did not differ between hydropeaking regimes. Condition was assessed using weight–length relationships and differed between rivers for each species, and between hydropeaking regimes for longnose dace and slimy sculpin. Survival of longnose dace and slimy sculpin was lower in the regulated river relative to the naturally flowing river, but comparable between rivers for trout‐perch. Annual growth was significantly related to mean summer discharge in the regulated river and to mean summer water temperature in the naturally flowing river for each species, and significantly different slopes among species indicate species‐specific responses to discharge and temperature alterations. This study demonstrates different biological responses among fish species within rivers to regulation in general, as well as to specific hydropeaking regimes. Future studies should focus on multiple species and multiple indicators of fish health to more fully characterize the impacts of river regulation on downstream fish communities. Copyright © 2016 John Wiley & Sons, Ltd.     

Annual Variation in Larval Fish Assemblages in a Heavily Regulated River During Differing Hydrological Conditions

One of the most severe anthropogenic impacts on river systems worldwide has been alterations to the natural flow regime. Understanding biological responses to altered flow regimes is critical to effectively rehabilitate aquatic ecosystems. This study investigated changes in the larval fish assemblages during varying hydrological conditions over 5 years in the lower River Murray, in south‐eastern Australia. Larval fish were sampled during spring/summer during three distinct hydrological periods: under a within‐channel flow pulse and a water level raising (2005); during a drought with very low flows and stable water levels (2006, 2007 and 2008); and during an overbank flow (2010). Data were analysed for annual, spatial and seasonal variations, and correlations were examined between changes in larval assemblages and environmental variables. Hydrology was a key driver in inter‐annual variation in larval fish assemblages. High abundances of small‐bodied to medium‐bodied native species were recorded under low flows, while for other species, abundance was more strongly correlated to temperature, representing seasonal variation. Two large‐bodied species were only recorded during the within‐channel flow pulse and overbank flow conditions, and significant increases in larval abundances were recorded during overbank flow conditions. We suggest groupings based on species response to hydrology (low‐flow to medium‐flow spawners, high‐flow spawners or seasonal spawners). This study suggests that a range of conditions (low flows and overbank flows) are required to maintain a diverse and abundant native fish fauna in the lower River Murray. Copyright © 2015 John Wiley & Sons, Ltd.     

Effects of Moderate and Extreme Flow Regulation on Populus Growth along the Green and Yampa Rivers,Colorado and Utah

River regulation induces immediate and chronic changes to floodplain ecosystems. We analysed both short‐term and prolonged effects of river regulation on the growth patterns of the keystone riparian tree species Fremont cottonwood (Populus deltoides ssp. wislizenii) at three upper Colorado River Basin rivers having different magnitudes of flow regulation. We compared cottonwood basal area increment on (i) the regulated Upper Green River below Flaming Gorge Dam; (ii) the adjacent free‐flowing Yampa River; and (iii) the partially regulated Lower Green River below their confluence. Our goal was to identify the hydrologic and climatic variables most influential to tree growth under different flow regimes. A dendrochronological analysis of 182 trees revealed a long‐term (37 years) trend of declining growth during the post‐dam period on the Upper Green, but trees on the partially regulated Lower Green maintained growth rates similar to those on the reference Yampa River. Mean annual, mean growing season, and peak annual discharges were the multicollinear flow variables most correlated to growth during both pre‐dam and post‐dam periods at all sites. Annual precipitation was also highly correlated with tree growth, but precipitation occurring during the growing season was poorly correlated with tree growth, even under full river regulation conditions. This indicates that cottonwoods rely primarily on groundwater recharged by river flows. Our results illustrate the complex and prolonged effects of flow regulation on floodplain forests, and suggest that flow regulation designed to simulate specific aspects of flow regimes, particularly peak flows, may promote the persistence of these ecosystems. Copyright © 2016 John Wiley & Sons, Ltd.     

The Impact of Low Flow on Riverine Food Webs in South‐Central Newfoundland

Low‐flow events can reduce food availability and decrease the feeding niche of consumers within rivers. Stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope and stomach content analyses were employed to evaluate resource use and overlap between fish species in a natural and regulated river in normal and low‐flow years, with the use of multiple methodological approaches providing the best means of understanding short‐term and long‐term observations on fish feeding and resource overlap under changing flow conditions. Diet analyses generally indicated significant inter‐specific differences in the diets of key fish species within rivers and similarities in resource use between rivers. In comparison with fish from the natural river, fish from the regulated river had lower and less inter‐annually variable δ¹³C values. In the natural river, there was a significant reduction and increase, respectively, in δ¹³C and δ¹⁵N variation in the low‐flow year. Intra‐annual or inter‐annual differences in trophic niche area were not apparent in the regulated river, whereas within the natural river, intra‐annual and inter‐annual differences in trophic niche were found. Resource overlap between key fish species was also higher in the low‐flow year and lower in the spring and higher in the summer as a result of differences in flow. Resource overlap was also higher between rivers in the low‐flow year. High resource overlap between rivers during decreased summer flow indicates a strong effect of flow on river organisms, where both fish and their invertebrate prey resources are concerned. Copyright © 2014 John Wiley & Sons, Ltd.     

Projected climate change impacts on hydrologic flow regimes in the Great Plains of Kansas

Alteration of flow regimes due to change in climate and its potential impact on habitat and species has become a major cause of concern for riverine ecosystems. Areas that are more vulnerable to such changes are semiarid river systems or regions experiencing intermittent flow and cyclic droughts. Although ecological changes are expected to occur with flow regime alterations, the biological changes cannot be predicted until the flow in such regions is analysed. This study addresses this concern by providing an analysis of flow for a semiarid river basin in the Central Great Plains from a 50 and 100‐year projection climate data. The projected data for these two periods are then compared with 30‐year historical data to determine changes in flow. Five major components of flow regime, magnitude, duration, and timing of annual extreme water conditions, frequency and duration of high and low pulses, and rate and frequency of water condition changes, were examined with respect to climate change for their impact on the ecology of the basin. This analysis strongly suggests that inter‐ and intra‐annual changes in flow regimes will result in the intensified drying of the basin represented by the increased number of low flow periods followed by higher occurrences of high flow events of shorter duration with expected changes in climate.     

The effect of altered flow regime on the frequency and duration of bankfull discharge: Murrumbidgee River,Australia

On meandering rivers with well‐developed floodplains, bankfull stage has geomorphological and ecological significance because it approximates the level of connection between the channel and the floodplain. As a river rises to bankfull stage, sediment begins to be deposited on the floodplain, wetlands are progressively inundated and organisms migrate between the channel and floodplain habitats. On many rivers large headwater dams have reduced the frequency and duration of floodplain inundation downstream. However, the lack of reliable pre‐regulation flow data has made it difficult to quantify the effects of river regulation. This study used historical regulated and modelled natural flow data to determine the effects of regulation on the frequency and duration of bankfull flows on the Murrumbidgee River, one of Australia's largest and most heavily regulated rivers. In combination with floodplain surveys the flow data show that regulation has halved the frequency and duration of bankfull flows. This reduction in channel–floodplain connection has implications for the ecological health of the Murrumbidgee River. Copyright © 2005 John Wiley & Sons, Ltd.     

The Sanaga discharge at the Edea Catchment outlet (Cameroon): An example of hydrologic responses of a tropical rain‐fed river system to changes in precipitation and groundwater inputs and to flow regulation

The Sanaga River is one of Sub‐Saharan Africa's largest and greatly regulated rivers. Available flow data for this hydrosystem largely cover the pre‐ and post‐regulation periods. From comparisons between unregulated (hypothetical) and observed scenarios, it has been possible to separate and to quantify hydro‐climatic (groundwater + rainfall) change effects from anthropogenic impacts (especially dam‐related alterations). To appreciate shifts in the river regime, discontinuity detection tests and the IHA model were applied to discharge data series reflecting average and extreme flow conditions, respectively. Results obtained principally from the Hubert segmentation method reveal that a major discontinuity occurred in 1970–1971 separating a surplus phase between 1945–1946 and 1969–1970, and a deficient and much contrasted one, from 1971/1972. This implies that the Sanaga catchment is dominantly affected by hydro‐climatic changes. However, wide land cover/land use changes experienced here since 1988 have resulted in an increase in surface runoff. Additional quickflows linked to these changes may have partly compensated for the substantial decline in the dry season rainfall and groundwater inputs observed from this date. Although at the monthly scale, dam‐related impacts on average flows increase with stage of regulation, the seasonal variability of the river regime remains generally unaffected. A comparison of the IHA statistics, calculated from unregulated and observed streamflow data, show that hydrologic shifts occurring in maximum and minimum discharges are mostly significant from 1971/1972 and are mainly due to the action of dams. Minimum flows appear, however, widely impacted, thus reflecting the prime objective assigned to the existing reservoirs, constructed to supplement flows for hydroelectricity production during the dry season. Copyright © 2010 John Wiley & Sons, Ltd.     

Rivers need floods: Management lessons learnt from the regulation of the Norwegian salmon river,Suldalslågen

The Norwegian river Suldalslågen, known for its population of large‐sized Atlantic salmon (Salmo salar), has been regulated for hydropower in 1966–1967 and in 1980. The initial regulation increased winter flows and reduced summer flows and major floods. The second regulation, involving abstraction of water to a power station in an adjacent fjord, led to a strong reduction in flow. In addition to implementing different flow regimes, many remedial actions have been taken, often concurrently, making it almost impossible to detect the effect of single measures. In addition, the monitoring data have not always been consistent as regards methods and scope, and also, few data are available for preregulation conditions. This highlights major challenges in the long‐term management of regulated rivers. The absence of major floods after regulation led to increased sedimentation and encouraged carpet mosses. This reduced interstitial spaces, creating a poor habitat for salmon fry and benthic invertebrates. The knowledge gained from the wide‐ranging studies of the different flow regimes have enabled the environmental authorities to devise a final regulation regime from 2012. The final flow regime focused on biological values and functions to sustain the strain of wild, large adult salmon. The catch of wild salmon >7 kg has in fact increased since 2010 and stabilized between 1 and 2 metric tons, although the yield of large salmon prior to 1994 is unknown. In addition, the increase in the catch of large salmon is based on hatchery fish. Hatchery fish have also to a large extent contributed to the increase in the total salmon catch in recent years. Thus, that the catches in Suldalslågen are now at an all‐time high is not due to improved conditions in the river but likely to hatchery fish.     

Effects of hydropeaking operations on the growth of Alabama bass Micropterus henshalli and redeye bass Micropterus coosae in the Tallapoosa River,Alabama, USA

Anthropogenic factors such as dam construction and hydropower generation can dramatically alter the flow regime of rivers and may impact growth of aquatic organisms. Using incremental growth techniques, annual growth of Alabama bass Micropterus henshalli and redeye bass M. coosae in the Tallapoosa River, Alabama, USA, was evaluated in response to variation in flow regime. Fish were collected from the Tallapoosa River above Harris Dam (unregulated site) and at two sites downstream of the dam (regulated sites), as well as Hillabee Creek (unregulated tributary). Flow variables were calculated for each growth year, and the best model that described growth for each species at each location was determined using Akaike's Information Criterion. Additionally, growth increments of each species at ages 1, 2, and 3 were compared between years characterized by low and high flow variability. Age was the best explanatory variable that described growth in all models, although flow variables were included in more than half the models. In all cases, annual and seasonal flow variables had low predictive power and explained <2% of the variation in growth. Growth was higher for age‐1 fish in years with less flow variation but was similar among years for age‐2 and age‐3 fish. Overall, this study provided little evidence that annual growth of either species was heavily influenced by flow in this regulated river.     

Macroinvertebrate Community Responses to Annual Flow Variation from River Regulation: An 11‐Year Study

The majority of the world's large river systems is affected by dams. The influences of unnatural regimes induced by flow management are wide‐ranging from both biotic and abiotic standpoints. However, many of these effects are not evident over short (1–2 years) periods (e.g. impacts of annual flow variation). This study examines the long‐term effects of annual flow variation on the macroinvertebrate community in the Chattahoochee River (GA) in the reaches below Buford Dam, the major water control structure on the river. Quarterly, macroinvertebrate samples were taken from 2001 to 2011 using Surber and Hester–Dendy plate samplers at six locations spread across 65 km below the dam. Data were analysed via analysis of similarities to determine differences in community composition between high‐flow (mean discharge = 58.27 m³/s) and low‐flow (mean discharge = 26.53 m³/s) years. Taxa that contributed most to community differences were determined via similarity percentages analyses and subsequent t‐tests. Several insect taxa (e.g. Cheumatopsyche and Ceratopsyche caddisfly larvae, Maccaffertium mayfly nymphs and Taeniopteryx stonefly nymphs) were more prevalent under the high‐flow regime. Non‐insect macroinvertebrates (e.g. Crangonyx amphipods, Tricladida flatworms and Caecidotea isopods) were more abundant under low‐flow conditions. In terms of taxon richness, no significant effects of flow regime were detected. Implications of macroinvertebrate patterns for the fishery and ecological health of the river are discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

The Hydrological Status Concept: Application at a Temporary River (Candelaro,Italy)

In achieving the final objective of the European Water Framework Directive, the evaluation of the ‘hydrological status’ of a water body in a catchment is of the utmost importance. It represents the divergence of the actual hydrological regime from its ‘natural’ condition and may thus provide crucial information about the ecological status of a river. In this paper, a new approach in evaluating the hydrological status of a temporary river was tested. The flow regime of a river has been classified through the analysis of two metrics: the permanence of flow and the predictability of no‐flow conditions that were evaluated on monthly streamflow data. This method was applied to the Candelaro river basin (Puglia, Italy) where we had to face the problem of limited data availability. The Soil and Water Assessment Tool model was used when streamflow data were not available, and a geographic information system procedure was applied to estimate potential water abstractions from the river. Four types of rivers were identified whose regimes may exert a control on aquatic life. By using the two metrics as coordinates in a plot, a graphic representation of the regime can be visualized in a point. Hydrological perturbations associated with water abstractions, point discharges and the presence of a reservoir were assessed by comparing the position of the two points representing the regime before and after the impacts. The method is intended to be used with biological metrics in order to define the ecological status of a stream, and it could also be used in planning the ‘measures’ aimed at fulfilling the Water Framework Directive goals. Copyright © 2014 John Wiley & Sons, Ltd.     

Fish assemblage patterns across a gradient of flow regulation in an Australian dryland river system

Hydrological regime, physical habitat structure and water chemistry are interacting drivers of fish assemblage structure in floodplain rivers throughout the world. In rivers with altered flow regimes, understanding fish assemblage responses to flow and physico‐chemical conditions is important in setting priorities for environmental flow allocations and other river management strategies. To this end we examined fish assemblage patterns across a simple gradient of flow regulation in the upper Murray–Darling Basin, Australia. We found clear separation of three fish assemblage groups that were spatially differentiated in November 2002, at the end of the winter dry season. Fish assemblage patterns were concordant with differences in water chemistry, but not with the geomorphological attributes of channel and floodplain waterholes. After the summer‐flow period, when all in‐channel river sites received flow, some floodplain sites were lost to drying and one increased in volume, fish assemblages were less clearly differentiated. The fish assemblages of river sites did not increase in richness or abundance in response to channel flow and the associated potential for increased fish recruitment and movement associated with flow connectivity. Instead, the more regulated river's fish assemblages appeared to be under stress, most likely from historical flow regulation. These findings have clear implications for the management of hydrological regimes and the provision of environmental flows in regulated rivers of the upper Murray–Darling Basin. Copyright © 2010 John Wiley & Sons, Ltd.     

CLASSIFICATION OF FLOW REGIMES FOR ENVIRONMENTAL FLOW ASSESSMENT IN REGULATED RIVERS: THE HUAI RIVER BASIN,CHINA

Flow regime characteristics (magnitude, frequency, duration, seasonal timing and rates of change) play a primary role in regulating the biodiversity and ecological processes in rivers. River classification provides the foundation for comparing the hydrologic regimes of rivers and development of hydro‐ecological relationships to inform environmental flow management and river restoration. This paper presents a classification of natural flow regimes and hydrologic changes due to dams and floodgates in the Huai River Basin, China, in preparation for an environmental flow assessment. The monthly natural flow regime of 45 stations in the upper and middle Huai River Basin were simulated for the period 1963–2000, based on the hydrological model SWAT (Soil and Water Assessment Tool). Six classes of flow patterns (low or high discharge, stable or variable, perennial or intermittent, predictable or unpredictable) were identified based on 80 hydrologic metrics, analysed by hierarchical clustering algorithms. The ecologically relevant climatic and geographic characteristics of these flow classes were tested for concordance with, and to strengthen, the hydro‐ecological classification. The regulation of natural flow patterns by dams and floodgates changed flows at some locations within each flow class and caused some gauges to shift into another class. The research reported here is expected to provide a foundation for development of hydro‐ecological relationships and environmental flow methods for wider use in China, as well as setting a new scientific direction for integrated river basin management in the Huai River Basin. Copyright © 2011 John Wiley & Sons, Ltd.     

An Optimal Reservoir Operation Model Based on Ecological Requirement and Its Effect on Electricity Generation

Rather than optimizing water regimes for one or a few species, a better approach is to approximate the natural flow regime that maintains the entire panoply of species. RVA method generally describes flow regimes through 32 hydrologic indicators, quantifies the changes of the indicators post-dam, and distinguishes the highly changed indicators. Based on this function, an ecological objective which takes natural flow regimes into consideration is established. The objective synthesize highly changed indicators selected from the 32 hydrologic indicators and minimize their degree of change to approximate the natural status. The function of the hydrologic indicators are quantified through fuzziology according to their effect on river environment when changed. The model is applied to Xiangyang section of the Han River downstream the Danjiangkou reservoir, which maximizes the ecological objective to close to a natural flow regime. By optimization, model results indicate that the maximum synthetical membership of the selected indicators is 0.5, which means that the post-regulation optimum release is 50?% closer to the natural flow regime. It is much better than the traditional power generation regulation model, the membership of which is only 0.2. The result indicates that the ecological model is better in improving the river ecosystem, but with reduced power generation because of excessive abandon water. However, when deeply evaluate the effect of the new model, it shows the possibility of a win-win scenario between maintaining ecosystem health and power generation.