Assessment of Water Capacity and Availability from Unregulated Stream Flows Based on Ecological Limits of Hydrologic Alteration (ELOHA) Environmental Flow Standards

Determination of water resources management thresholds, such as conservation releases, passby flows, and water availability limits, is a contemporary challenge facing water resources managers. With recent advancements in environmental flow science, including the ecological limits of hydrologic alteration (ELOHA) framework, environmental flow standards can be developed for a variety of stream types throughout a particular region or watershed. Environmental flow standards typically cover the entire natural flow regime, including low‐flow, seasonal‐flow (medium), and high‐flow components. However, it can be difficult for water resources managers to directly apply these standards to establish practical management thresholds. This study proposes a novel approach to assessing water capacity based on ELOHA environmental flow standards. The procedure entails iterative simulations to identify withdrawal limits for gaged streams and regional regression analysis to predict withdrawal limits for ungaged streams. The approach was applied for 63 reference gages with long‐term, continuous, minimally altered, daily streamflow records within the Susquehanna River basin. The results of the investigation demonstrate that the approach can be used to assess water capacity from gaged and ungaged streams via iterative withdrawal simulations and regional regression analysis respectively. The regression equation developed through analysis of the reference gages has an adjusted R‐square value of 0.96 and a standard error of 27%. Determination of a water capacity value, based on a suite of environmental flow standards, provides water resources managers with a valuable tool for informing the establishment of water resources management thresholds. Copyright © 2015 John Wiley & Sons, Ltd.     

REGIONAL FRAMEWORKS APPLIED TO HYDROLOGY: CAN LANDSCAPE‐BASED FRAMEWORKS CAPTURE THE HYDROLOGIC VARIABILITY?

Regional frameworks have been used extensively in recent years to aid in broad‐scale management. Widely used landscape‐based regional frameworks, such as hydrologic landscape regions (HLRs) and physiographic provinces, may provide predictive tools of hydrologic variability. However, hydrologic‐based regional frameworks, created using only streamflow data, are also available and have been created at various scales; thus, relating frameworks that share a common purpose can be informative. In addition, identifying how the relative importance of variables change in governing streamflow with respect to scale can also be informative. The purpose of this study was to determine whether landscape‐based frameworks could explain variation in streamflow classifications and in the hydrologic variables used in their creation. We also evaluated how climate and watershed‐based variables govern the divergence of different flow classifications at two different scales. HLRs and physiographic provinces poorly predicted flow class affiliation within our study and for the entire USA, although physiographic provinces explained more variability. We also found that HLRs explained very little variation in individual hydrologic parameters. Using variables summarized at the watershed scale, we found that climate will play a larger role in influencing hydrology across the entire US, whereas soils may govern variation in hydrology at smaller scales. Our results suggest that predictor variables, developed at the watershed scale, may be the most appropriate at explaining hydrology and that the variables used in creating regional landscape‐based frameworks may be more useful than the frameworks themselves. In addition, managers should be careful when using landscape‐based regional classifications for stream management because the scale of their construction may be too broad to capture differences in flow variability. Copyright © 2011 John Wiley & Sons, Ltd.     

Potential Effects of Climate Change on Ecologically Relevant Streamflow Regimes

We assessed the climate‐driven changes in ecologically relevant flow regimes expected to occur by the year 2100 in streams across the conterminous United States. We used long‐term daily flow measurements from 601 gauged streams whose watersheds were in relatively natural condition to characterize spatial variation in 16 flow regime variables selected for their ecological importance. Principal component analysis of these 16 variables produced five uncorrelated factors that described patterns of spatial covariation in flow regimes. These five factors were associated with low flow, magnitude, flashiness, timing, and constancy characteristics of the daily flow regime. We applied hierarchical clustering to the five flow factors to classify the 601 streams into three coarses and eight more finely resolved flow regime classes. We then developed a random forest model that used watershed and climate attributes to predict the probabilities that streams belonged to each of the eight finely resolved flow regime classes. The model had a prediction accuracy (per cent correct classification) of 75%. We used the random forest model with downscaled climate (precipitation and temperature) projections to predict site‐specific changes in flow regime classes expected by 2100. Thirty‐three per cent of the 601 sites were predicted to change to a different flow regime class by 2100. Snow‐fed streams in the western USA were predicted to be less likely to change regimes, whereas both small, perennial, rain‐fed streams and intermittent streams in the central and eastern USA were predicted to be most likely to change regime. Copyright © 2016 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.     

Predicting the natural flow regime: models for assessing hydrological alteration in streams

Understanding the extent to which natural streamflow characteristics have been altered is an important consideration for ecological assessments of streams. Assessing hydrologic condition requires that we quantify the attributes of the flow regime that would be expected in the absence of anthropogenic modifications. The objective of this study was to evaluate whether selected streamflow characteristics could be predicted at regional and national scales using geospatial data. Long‐term, gaged river basins distributed throughout the contiguous US that had streamflow characteristics representing least disturbed or near pristine conditions were identified. Thirteen metrics of the magnitude, frequency, duration, timing and rate of change of streamflow were calculated using a 20–50 year period of record for each site. We used random forests (RF), a robust statistical modelling approach, to develop models that predicted the value for each streamflow metric using natural watershed characteristics. We compared the performance (i.e. bias and precision) of national‐ and regional‐scale predictive models to that of models based on landscape classifications, including major river basins, ecoregions and hydrologic landscape regions (HLR). For all hydrologic metrics, landscape stratification models produced estimates that were less biased and more precise than a null model that accounted for no natural variability. Predictive models at the national and regional scale performed equally well, and substantially improved predictions of all hydrologic metrics relative to landscape stratification models. Prediction error rates ranged from 15 to 40%, but were ≤25% for most metrics. We selected three gaged, non‐reference sites to illustrate how predictive models could be used to assess hydrologic condition. These examples show how the models accurately estimate pre‐disturbance conditions and are sensitive to changes in streamflow variability associated with long‐term land‐use change. We also demonstrate how the models can be applied to predict expected natural flow characteristics at ungaged sites. Copyright © 2009 John Wiley & Sons, Ltd.     

Ecological effects of flow regulation on macroinvertebrate and periphytic diatom assemblages in the Hawkesbury–Nepean River,Australia

The effects of flow regulation on macroinvertebrates and periphytic diatoms were examined in the Hawkesbury–Nepean River system in Australia. Regulated sites below eight dams or weirs were compared with unregulated sites above the impoundments and sites on two nearby unregulated streams. The management of the water supply during the study created two types of flow regulation, sites with water supply releases and sites with comparatively small or no releases. The macroinvertebrate communities in three habitats and periphytic diatoms below the storages and weirs differed from the biota at unregulated sites above the weirs and on unregulated systems. The number of macroinvertebrate taxa in riffle and pool‐rock assemblages was significantly lower at regulated sites when compared with unregulated sites and the number of stream edge macroinvertebrate and diatom taxa was unaffected by regulation. Riffle and pool‐rock macroinvertebrate assemblages differed between the two types of regulation. However, periphytic diatom and edge habitat macroinvertebrate assemblages did not differ between the two types of flow regulation. Examination of environmental variables associated with the change in the biota suggested that the principal effect of the management of the water supply system in the Hawkesbury–Nepean River was changed hydrology rather than altered water quality. Copyright © 2001 John Wiley & Sons, Ltd.     

Effects of flow regulation on hydrologic patterns of a large,inland delta

The Peace–Athabasca River Delta (PAD) is one of the largest freshwater deltas and most biologically productive in the world. Because regional evaporation is greater than precipitation, the thousands of lakes and wetlands dotting this area rely on periodic flooding from the Peace and Athabasca rivers to be replenished. Flood frequency significantly declined beginning in the mid‐1970s, several years after the initiation of flow regulation of the Peace River. However, the drying trend was interrupted in 1996 when the PAD experienced extensive inland inundation on two separate occasions, one in the spring and one in the summer. A one‐dimensional numerical hydrodynamic model was used to evaluate the role of flow regulation and hydroclimatic conditions on the water levels of major lakes found in the PAD. Three Peace River flow scenarios were analysed: the observed flows, the flow regime without the ‘precautionary drawdown’ spill which was required because of the discovery of a sinkhole at the crest of the dam, and the naturalized flow regime, which assumed no dam regulation. Modelling results indicated that the effect of the spill on the flow regime within the PAD was approximately equivalent in magnitude, although different in timing, to what would have resulted from the prevailing hydroclimatic conditions in an unregulated system. Furthermore, even in the absence of the precautionary drawdown spill, the lake levels would have risen well above the maximum daily average, suggesting that 1996 was one of the wettest years on record. Finally, the hydrodynamic regime observed at the end of the summer 1996 was very similar to that modelled under unregulated flow conditions, suggesting that flow regulation could be used to alter the hydrodynamic regime of a large delta to at least partially restore natural conditions and potentially improve ecosystem health. Copyright © 2001 John Wiley & Sons, Ltd.     

Benthic Response to Flow Alteration in a New Mexico Arid Mountain Stream

Past and current pressure on streams and rivers for consumptive use requires the development of tools and decision‐making processes for water managers to minimize impacts on ecological function. This paper examines the utility of modeling benthic biomass in relation to benthic macroinvertebrate (BMI) community attributes for water resource management scenarios in the Cliff‐Gila Valley of the Gila River, New Mexico, USA. The river benthos biomass model (RivBio) was used in conjunction with hydraulic modeling to predict growth and decline of benthic biomass. BMI community attributes were compared along gradients of hydrologic impact (successive existing diversions) in the Cliff Gila Valley and were compared to community attributes in similar regional streams. Benthic biomass was minimally affected by proposed diversions at flows above 4.25 cms (150 cfs), but was severely reduced downstream because of existing diversions during lower flow periods. Riffle habitat was disproportionately affected during extreme low and interrupted flow, which may have resulted in BMI communities shifted towards multi‐habitat generalists that can persist in lentic conditions. Flow augmentation from proposed diversions and storage would greatly mitigate these existing biomass losses by providing consistent base flow and lotic conditions in riffle habitat. Both benthic biomass and BMI community endpoints were useful when comparing water management scenarios. Copyright © 2016 John Wiley & Sons, Ltd.     

Characterizing Sub‐Daily Flow Regimes: Implications of Hydrologic Resolution on Ecohydrology Studies

Natural variability in flow is a primary factor controlling geomorphic and ecological processes in riverine ecosystems. Within the hydropower industry, there is growing pressure from environmental groups and natural resource managers to change reservoir releases from daily peaking to run‐of‐river operations on the basis of the assumption that downstream biological communities will improve under a more natural flow regime. In this paper, we discuss the importance of assessing sub‐daily flows for understanding the physical and ecological dynamics within river systems. We present a variety of metrics for characterizing sub‐daily flow variation and use these metrics to evaluate general trends among streams affected by peaking hydroelectric projects, run‐of‐river projects and streams that are largely unaffected by flow altering activities. Univariate and multivariate techniques were used to assess similarity among different stream types on the basis of these sub‐daily metrics. For comparison, similar analyses were performed using analogous metrics calculated with mean daily flow values. Our results confirm that sub‐daily flow metrics reveal variation among and within streams that are not captured by daily flow statistics. Using sub‐daily flow statistics, we were able to quantify the degree of difference between unaltered and peaking streams and the amount of similarity between unaltered and run‐of‐river streams. The sub‐daily statistics were largely uncorrelated with daily statistics of similar scope. On short temporal scales, sub‐daily statistics reveal the relatively constant nature of unaltered stream reaches and the highly variable nature of hydropower‐affected streams, whereas daily statistics show just the opposite over longer temporal scales. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.     

Potential ecological effects of water extraction in small,unregulated streams

River regulation can have various effects on the natural flow regime, however the most obvious and perhaps pronounced hydrological effect is the reduction of total water discharge. Whilst there has been an increasing number of studies investigating the impacts of river regulation on lowland rivers, few studies have specifically investigated the effects of water extractions on small upland streams. In this study, we experimentally examined the effects of short‐term, summer water extractions from small, unregulated streams. Five 30 m reaches were experimentally manipulated to divert a proportion of the total stream flow, and another five 30 m reaches were designated as controls, in the Yea River catchment, Victoria, Australia. The percentage of total discharge diverted from each experimental reach varied through time and between creeks (28–97%), with discharge always significantly reduced compared to control locations. All sites were monitored for available habitat, biofilm, water quality and macroinvertebrate diversity and density, fortnightly during February and March 2004. Despite the range of total stream volumes being extracted, the manipulation altered important ecological components of these unregulated creeks, including changes in physical habitat features (reduced stream wetted area and maximum stream depth) and reduced dissolved oxygen concentrations. Biofilm parameters showed a slight increase in diverted reaches, but were not statistically different from the controls. There was no statistical difference in total density of macroinvertebrates or EPT taxa; however, the density of Austrocercella mariannae (Notonemouridae) was significantly reduced in diverted reaches. Macroinvertebrate family level diversity, and the family diversity of grazers and shredders was reduced in diverted reaches. This study demonstrates that there are likely to be significant ecological impacts of extracting water in unregulated creeks. Whilst this study has demonstrated the need to consider environmental water requirements in unregulated streams, further studies are required to inform the debate about the volume, timing and predicted ecological response with improved environmental water. Copyright © 2006 John Wiley & Sons, Ltd.     

Landscape and flow path-based nutrient loading metrics for evaluation of in-stream water quality in Saginaw Bay,Michigan

Landscape metrics are often used to model nonpoint source pollution from agricultural and urban surface runoff. By considering topography and the spatial arrangement of land cover, landscape metrics can better account for hydrologic connectivity, loading quantity, and vegetated buffer filtering between nutrient loading sources and streams. For this study we develop a surface runoff nutrient loading metric that considers source (i.e. cropland or developed) loading and buffer filtering along hydrologic transport vectors, or flow paths. We use General Additive Modeling to evaluate the relationship between this metric and in-stream nitrogen (N) and phosphorus (P) concentrations in the Saginaw Bay watershed in Michigan, US and compare the relative predictive power between this metric and other landscape metrics that do not consider hydrologic connectivity. The flow path-based cropland loading metric was a stronger predictor of in-stream NO₃ concentrations than alternative metrics. In-stream P concentrations were best predicted by models that included 48-h antecedent precipitation and catchment-wide proportion of developed landcover. Metric maps reveal high nutrient loading areas where only a small proportion of loading reaches streams via surface runoff, highlighting the need to consider nutrient loading via drainage tiles and other subsurface pathways in efforts to quantify nonpoint source loading to surface waters. The flow path-based loading metric is represented spatially as a gridded dataset showing estimates of nutrient loading adjacent to streams, and with higher resolution stream delineation data it could be used by land managers to target locations for precision buffer placement to intercept surface runoff and reduce nutrient loading.     

Hydrologic Variability Influences Local Probability of Pallid Sturgeon Occurrence in a Missouri River Tributary

A river's flow regime creates and maintains spatial variability in habitat and dictates the distribution and abundance of riverine fishes. Changes to patterns of natural hydrologic variation and disturbance create novel flow conditions and may influence distribution of native fishes. We examined local and regional‐scale factors that influenced the presence of pallid sturgeon Scaphirhynchus albus in the Platte River, a large tributary to the Missouri River in Nebraska, USA. Daily river discharge, diel flow variability, season and location in the study area were the most supported variables in logistic regression models explaining pallid sturgeon distribution. The probability of pallid sturgeon occurrence was greatest during periods of high discharge (>90th percentile flows) in the spring and fall. Pallid sturgeon occurrence was always lower when variability in diel flow patterns was high (i.e. hydropeaking). Our results indicate that pallid sturgeon use of the lower Platte River was strongly tied to the flow regime. Therefore, the lower Platte River may provide an opportunity to preserve and restore sturgeon and possibly other large‐river fishes through appropriate water management strategies. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydrologic spiralling: the role of multiple interactive flow paths in stream ecosystems

We develop and illustrate the concept of ‘hydrologic spiralling’ using a high‐resolution (2 × 2 m grid cell) simulation of hyporheic hydrology across a 1.7 km² section of the sand, gravel and cobble floodplain aquifer of the upper Umatilla River of northeastern Oregon, USA. We parameterized the model using a continuous map of surface water stage derived from LIDAR remote sensing data. Model results reveal the presence of complex spatial patterns of hyporheic exchange across spatial scales. We use simulation results to describe streams as a collection of hierarchically organized, individual flow paths that spiral across ecotones within streams and knit together stream ecosystems. Such a view underscores the importance of: (1) gross hyporheic exchange rates in rivers, (2) the differing ecological roles of short and long hyporheic flow paths, and (3) the downstream movement of water and solutes outside of the stream channel (e.g. in the alluvial aquifer). Hydrologic spirals underscore important limitations of empirical measures of biotic solute uptake from streams and provide a needed hydrologic framework for emerging research foci in stream ecology such as hydrologic connectivity, spatial and temporal variation in biogeochemical cycling rates and the role of stream geomorphology as a dominant control on stream ecosystem dynamics. Copyright © 2008 John Wiley & Sons, Ltd.     

Determining the effects of dams on subdaily variation in river flows at a whole‐basin scale

River regulation can alter the frequency and magnitude of subdaily flow variations causing major impacts on ecological structure and function. We developed an approach to quantify subdaily flow variation for multiple sites across a large watershed to assess the potential impacts of different dam operations (flood control, run‐of‐river hydropower and peaking hydropower) on natural communities. We used hourly flow data over a 9‐year period from 30 stream gages throughout the Connecticut River basin to calculate four metrics of subdaily flow variation and to compare sites downstream of dams with unregulated sites. Our objectives were to (1) determine the temporal scale of data needed to characterize subdaily variability; (2) compare the frequency of days with high subdaily flow variation downstream of dams and unregulated sites; (3) analyse the magnitude of subdaily variation at all sites and (4) identify individual sites that had subdaily variation significantly higher than unregulated locations. We found that estimates of flow variability based on daily mean flow data were not sufficient to characterize subdaily flow patterns. Alteration of subdaily flows was evident in the number of days natural ranges of variability were exceeded, rather than in the magnitude of subdaily variation, suggesting that all rivers may exhibit highly variable subdaily flows, but altered rivers exhibit this variability more frequently. Peaking hydropower facilities had the most highly altered subdaily flows; however, we observed significantly altered ranges of subdaily variability downstream of some flood‐control and run‐of‐river hydropower dams. Our analysis can be used to identify situations where dam operating procedures could be modified to reduce the level of hydrologic alteration. Copyright © 2009 John Wiley & Sons, Ltd.     

Do Environmental Stream Classifications Support Flow Assessments in Mediterranean Basins?

Natural flow regimes are of primary interest in designing environmental flows and therefore essential for water management and planning. The present study discriminated natural hydrologic variation using two different environmental classifications (REC-Segura and WFD-ecotypes) and tested their agreement with an a posteriori (hydrologic) classification in a Spanish Mediterranean basin (the Segura River, SE Spain). The REC-Segura was developed as a two-level hierarchical classification based on environmental variables that influence hydrology (climate and source-of-flow). The WFD-ecotypes were developed by the Spanish Ministry for the Environment to implement the Water Framework Directive (WFD) using hierarchical hydrologic, morphologic and physicochemical variables. The climate level in the REC-Segura broadly described the hydrologic pattern observed along the NW-SE aridity gradient of the basin. However, source-of-flow (defined by karstic geology) was only able to discriminate variation in flow regimes within one climatic category. The WFD-ecotypes, despite incorporating hydrologic variables, did not fully discriminate hydrologic variation in the basin. Ecotypes in tributary streams located in dry or semiarid climates embrace different flow regimes (both perennial and intermittent). There was little agreement between environmental and hydrologic classifications. Therefore, the authors advise against the use of environmental classifications for the assessment of environmental flows without first testing their ability to discriminate hydrologic patterns.     

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.     

Diversity of river fishes influenced by habitat heterogeneity across hydrogeomorphic divisions

Freshwater fish communities are structured through complex interactions among multiple spatial scales. Efforts to conserve and rehabilitate fish communities in riverine systems can benefit from an understanding of how processes across spatial scales influence species diversity patterns. We assessed species diversity at different hierarchical spatial scales and changes in species composition along the longitudinal gradient of the Niobrara River basin, Great Plains, USA. We assessed the contribution of α‐ and β‐diversity components to γ‐diversity at five spatial scales (i.e., mesohabitat, site, reach, segment, and river) using an additive partitioning approach. The observed mean β‐diversity was significantly greater than expected at the site, reach, and segment spatial scales. The most significant difference between expected and observed β‐diversity occurred at the segment spatial scale and suggests differences in community structure along the Niobrara River. Additive partitioning of diversity components provided a framework with which to assess patterns at multiple hierarchical levels. Our results suggest that changes in channel geomorphic and hydrologic conditions provide the impetus for species sorting resulting in unique fish assemblages along the Niobrara River. Conservation of species diversity for Great Plains fishes and other similar systems will likely benefit from considering species filtering processes at multiple spatial scales and maintaining intact hydrologic regimes across unique geomorphic boundaries.