Instream Flow Research Articles

Evaluation and Re-estimation of Instream Flow Considering the Water Quality and Aquatic Ecosystem of the Seomjingang River Watershed

In this study, the appropriateness of the current publicly announced and managed instream flow in the Seomjingang River watershed was evaluated based on the water quantity, water quality, and state of the aquatic ecosystem. The stream flow was evaluated based on the observed water flow rate at the Gurye-gun (Songjeong-ri) station that is the main point of the Seomjingang River flow management and located at the lowest downstream of the main stream of the Seomjingang River. Another important reason for choosing this station was that observational data from before the construction of the major dam to the present day were available. The water quality and aquatic ecosystem conditions were reviewed based on the data measured over the past 20 years, and the achievement ratio of instream flow was compared with that of stations in the other major river systems. Based on the evaluation result, the instream flow was re-estimated for the 11 important stations of the Seomjingang River and its two branches. Based on the currently permitted water use of the Seomjingang River, the amount of water required to supply for the instream flow deficit during dry seasons was predicted and presented as a reference for water management work.

The use of umbrella fish species to provide a more comprehensive approach for freshwater conservation management

Abstract Where freshwater species populations are in decline, conservation management requires rapid, cost‐effective approaches to develop recommendations, particularly at broad geographical scales or where species‐specific information is lacking. The umbrella species approach, typically applied to terrestrial taxa, is one potentially useful option to inform large‐scale freshwater management efforts. A quantitative, integrated approach is proposed for selecting suites of umbrella fish species over diverse spatial scales using a combination of species ranges, life‐history traits, and species vulnerability scores. The approach also uses expert opinion to validate methods and results. This approach was applied to native fishes in California, and results for two river basins are explored in the context of instream flow management. These examples illustrate how the results could help address two common instream flow management challenges in California: (i) the lack of information related to species‐specific flow requirements in basins with many species; and (ii) the need to move beyond a single species approach to flow management. In addition, the results indicate that the protection of native fishes in California would provide co‐benefits for other aquatic and riparian taxa. A key benefit of this approach is that the data used to select suites of umbrella species (e.g. species ranges, life‐history traits, climate vulnerabilities) are widely available at varying degrees of specificity for most freshwater fishes. Therefore, this flexible approach could be applied in other regions to aid managers in making freshwater conservation decisions, such as for instream flow strategies, in an efficient and cost‐effective manner.

The Economic and Environmental Benefits of Partial Leasing of Agricultural Water Rights

AbstractBalancing out‐of‐stream water demands and ecological instream flows is a difficult challenge in watershed‐scale management. Many watersheds already experience acute and chronic water shortages during average runoff years and may face more frequent and severe droughts in some locations due to climate and demographic change. Water markets may mitigate the economic consequences of shortages, but their potential is limited by the prevalence of all‐or‐nothing irrigate‐or‐fallow crop water use strategies. Irrigation water generally provides diminishing returns for crop productivity, so it may be possible to reduce water application at the margin with only a small loss in crop production, creating water savings that could be leased for other uses. We explore this scenario by combining a crop growth and hydrology (CropSyst) model with an economic model of farm profits and water trading, and apply it to the Walla Walla Basin in Washington State. Our results suggest that partial leasing of water rights through a deficit‐irrigation strategy could economically benefit annual crop growers while meaningfully increasing water availability for stream flow augmentation.

Hydraulic Properties of the Riffle Crest and Applications for Stream Ecosystem Management

AbstractRiffle crests are important hydraulic controls in riffle‐pool‐dominated streams, influencing pool hydraulics and water quality that collectively control lotic habitat for many organisms. We define a simple stream depth measurement, the riffle crest thalweg (RCT), describe measurement methods and utility, and suggest that RCT depth is a better independent variable than streamflow (Q) for many instream flow and habitat assessment applications. Using RCT depth as an independent variable, rather than streamflow, reduces the need for gauging or streamflow measurements in many management applications. Unlike streamflow, RCT depth varies directly with fundamental elements of riverine habitat such as channel morphology and bed roughness. We also suggest that relationships between RCT depth and streamflow (RCT‐Q curves) can be used to evaluate the risk of streamflow alteration at ungauged sites. We describe three case studies to demonstrate the utility of RCT depth and RCT‐Q rating curves in stream ecosystem management: (1) evaluating the effect of a top‐down flow prescription on modeled salmonid habitat, (2) estimating the risk from the incremental reduction of RCT depth on habitat and ecological responses, and (3) identifying relationships between RCT depth and dissolved oxygen in ungauged streams. An easy‐to‐measure, inexpensive, and ecologically sensitive metric, RCT depth holds promise as a useful tool in stream ecosystem management.

Evaluation of the impact of urban river bends on the enhancement of aquatic habitats using a two-dimensional habitat suitability model

The complex hydro-morphology of river bends plays an important role for creating and maintaining diverse habitat conditions for aquatic organisms. In this study,a dedicated standalone piece of software for benthic habitat simulation, which couples a two-dimensional (2D) depth-averaged water–sediment mathematical model with an instream flow incremental methodology, was devised to quantitatively evaluate the impact of channel bends on enhancing aquatic habitats. The multi-species integrated suitability index (CSI) curves based on three ecological variables were obtained. The test site was a 1.7-km-long stretch of the Jin Jiang River, which is a tributary of the Min Jiang River that flows through Huayang Town in Chengdu City, China. The potential value of aquatic habitats was quantitatively evaluated using the weighted usable area (WUA). The predicted WUA in the bend reach was 10.2%–16.6% greater than that in the straight reach. Moreover, the mean WUA decline rate was ~7.2% in the straight reach and ~5.6% in the bend reach. With increase in discharge, the WUA decreased more slowly in the bend reach compared to the straight reach. Our study indicates that for improving the aquatic habitats in urban rivers, the channel bends are beneficial. Compared with straight reaches, they not only could improve the availability of aquatic habitats but could also reduce the negative impact of the changes of discharge on the habitat. To summarize, this study provides a specific reference for ecological restoration.

Chinook salmon rearing habitat–discharge relationships change as a result of morphodynamic processes

AbstractRelationships between fluvial aquatic habitat availability and discharge are often assumed to remain static when used with hydrologic datasets to analyze changes in habitat availability over time. Despite this assumption, studies have observed significant changes in aquatic habitat availability before and after restoration projects, dam removals, and extreme flood events. However, research is lacking on how aquatic habitat changes as a result of morphodynamic processes during more commonly occurring hydrologic conditions. This study compared Chinook salmon (Oncorhynchus tshawytscha) rearing habitat availability at 19 discharges before and after a relatively mild 8‐year hydrologic period punctuated with modest floods on the lower Yuba River in California, USA. During this time, the total area of rearing habitat remained relatively consistent at discharges <2× bankfull but decreased by up to 25% at discharges >2× bankfull. Significant decreases in rearing habitat area appeared to be the result of widespread erosion on floodplains, terraces, and lateral bars, even after only modest floods. As a result, spatially delineated areas of lost habitat tended to increase in water depth and velocity at baseflow, bankfull, and floodplain‐filling discharges, while areas of gained habitat decreased in depth and velocity. Although these specific results may not apply to all rivers around the world, the finding that habitat–discharge relationships change as a result of morphodynamic processes likely does transfer globally and should be considered when making long‐term regulatory and management decisions, such as instream flow requirements and habitat restoration plans.

Evaluation of a geomorphic instream flow tool for conducting hydraulic‐habitat modelling

AbstractConventional hydraulic‐habitat modelling methods are time‐consuming to implement. In response to repeated calls for more efficient and practical approaches, researchers have developed a geomorphic instream‐flow tool (GIFT) that combines a method to simulate reach‐averaged hydraulics at flows less than bankfull and depth and velocity frequency distributions to develop streamflow‐fish habitat relationships. This approach requires fewer resources to implement than conventional methods, but it has not been widely adopted because it has been subject to minimal testing and validation. This study evaluates the performance of GIFT by comparing its outputs to empirical measurements and conventional model outputs from eight rivers in western North America. The results of this comparison indicate that the root mean square errors for average depth and velocity were 0.078 m and 0.047 m/s, respectively, and the fit of modelled depth and velocity frequency distributions was satisfactory (index of agreement >0.9) for 11 of 15 surveys for depth and 12 of 15 surveys for velocity. GIFT‐derived fish habitat‐streamflow relationships peaked at lower flows than benchmark relationships in smaller streams (mean annual discharge [MAD] < 0.15 m3/s) and are markedly differed from the benchmark in the largest river (MAD of 87 m3/s). GIFT was also paired with a geomorphic regime model to predict the direction of changes in channel morphology and fish habitat following forest harvesting in one watershed. GIFT provides an alternative to conventional modelling approaches for single‐thread, gravel‐bed rivers with a MAD of around 15 m3/s or less. Application of this technique outside of these bounds, or in other regions should proceed with caution, as these scenarios have not been tested.

Quantifying flow–ecology relationships across flow regime class and ecoregions in South Carolina

The natural flow regime (i.e. magnitude, frequency, duration, timing and rate of change of flow events) is crucial for maintaining freshwater biodiversity and ecosystem services. Protecting instream flow from anthropogenic alterations first requires an understanding of the relationship between aquatic organisms and the flow regime. In this study, we used a unique framework based on random forest modeling to quantify effects of natural flow regime metrics on fish and macroinvertebrate assemblages across ecoregions and flow regime types in the state of South Carolina, USA. We found that all components of the natural flow regime affected both fish and benthic macroinvertebrate assemblages, suggesting that maintaining natural aspects of all flow regime components is critical for protecting freshwater diversity. We identified hydrologic metrics and flow regime components such as magnitude, frequency, and duration of flow events, that were associated with the greatest ecological responses for individual stream classes to help managers prioritize hydrologic and biological metrics of interest during environmental flow standard development. The response of aquatic organisms to hydrologic metrics varied across stream classifications and ecoregions, highlighting the importance of accounting for differences in flow regime and ecoregion when designing environmental flow standards. We provide a flexible framework based on statistical flow-ecology relationships that can be used to inform instream flow management and assess effects of flow alteration on riverine assemblages.

Can Managed Aquifer Recharge Overcome Multiple Droughts?

Frequent droughts, seasonal precipitation, and growing agricultural water demand in the Yakima River Basin (YRB), located in Washington State, increase the challenges of optimizing water provision for agricultural producers. Increasing water storage through managed aquifer recharge (MAR) can potentially relief water stress from single and multi-year droughts. In this study, we developed an aggregated water resources management tool using a System Dynamics (SD) framework for the YRB and evaluated the MAR implementation strategy and the effectiveness of MAR in alleviating drought impacts on irrigation reliability. The SD model allocates available water resources to meet instream target flows, hydropower demands, and irrigation demand, based on system operation rules, irrigation scheduling, water rights, and MAR adoption. Our findings suggest that the adopted infiltration area for MAR is one of the main factors that determines the amount of water withdrawn and infiltrated to the groundwater system. The implementation time frame is also critical in accumulating MAR entitlements for single-year and multi-year droughts mitigation. In addition, adoption behaviors drive a positive feedback that MAR effectiveness on drought mitigation will encourage more MAR adoptions in the long run. MAR serves as a promising option for water storage management and a long-term strategy for MAR implementation can improve system resilience to unexpected droughts.

InSTREAM 7: Instream flow assessment and management model for stream trout

AbstractMechanistic, individual‐based simulation models have been used for >25 years to overcome well‐known limitations of “habitat suitability” models. InSTREAM 7 is the latest of our individual‐based models for predicting the effects of flow and temperature regimes on stream salmonid populations. Unlike PHABSIM (or other methods based on habitat “quality,” e.g., as net rate of energy intake), inSTREAM mechanistically represents specific effects of flow and temperature on all life stages, and how those effects combine into testable predictions of population measures such as abundance, relative abundance of multiple trout species, and persistence. InSTREAM 7 is the first version to also represent the daily light cycle (dawn, day, dusk, and night) and how feeding, predation risk, and individual behavior vary among light phases. An example assessment illustrates the importance of inSTREAM's multiple mechanisms: predicted trout population response to flow and temperature regimes depended on the effects of sub‐lethal temperatures on feeding behavior and effects of temperature on egg survival and development, as well as how depth and velocity affected growth and predation risk. While its input data requirements are comparable to PHABSIM's, inSTREAM provides a more comprehensive framework for thinking about and predicting specific, well‐known effects of flow and temperature. It has also proven useful for designing and evaluating restoration projects and for prioritizing alternative management actions. InSTREAM 7 is free, open‐source, completely updated with recent literature, and implemented in the popular NetLogo software platform that makes customization easy.

Combined influences of irrigation diversions and associated subsurface return flows on river temperature in a semi‐arid region

AbstractIrrigation activities alter water distribution and storage in arid and semi‐arid regions worldwide. The removal of water from streams can drastically impact instream flows. However, irrigation water conveyance and application onto fields can create surface and subsurface hydrologic connections, or lateral inflows, that return some of this diverted water back to streams. Prior research has shown the impact of surface water diversions from streams on downstream warming that increases stress on aquatic species. However, the combined effects of flow depletion and irrigation‐enhanced lateral inflows on stream temperature and river ecosystems remains poorly studied. To further understand these relationships, we combined intensive field monitoring over three irrigation seasons and thermal aerial imagery to identify irrigation‐enhanced subsurface lateral inflow locations and evaluate their effects on stream flow and temperature patterns over a 2.5‐km highly depleted study reach. Considering variable hydrology, weather, flow diversions, channel geometry and lateral inflows, we found irrigation‐enhanced lateral inflows were the likely explanation for buffered longitudinal and diel warming patterns that prevented stressful or lethal thermal conditions for brown trout. These localized temperature effects were more pronounced in drier years, under high diversion rates and during high solar radiation intensity. We also found that lateral inflows corresponded with greater spatial variability of stream temperatures and potential thermal refugia. Study results illustrate the potential ecological consequences of reducing irrigation‐enhanced lateral inflows and highlight the importance of hydrologic monitoring in irrigated arid river valleys. The role and preservation of these lateral inflows should be considered in water resources management related to irrigation efficiency and environmental flows.

R2Cross: A Web‐Based Decision Support Tool for Instream Flows

AbstractThe determination of instream flows for preserving or improving aquatic ecosystems’ health often includes challenges caused by varied hydraulic conditions, ecological criteria, and socioeconomic considerations. Despite the abundance of available methodologies, there are few available desktop or online applications enabling rapid assessment of instream flows that incorporate pertinent geospatial information for the region. We present R2Cross, a user‐friendly, online, instream flow rate calculation tool that was developed for aiding water allocation decisions in the state of Colorado. The R2Cross tool is the only existing online decision support tool based on a hydraulic rating method. It estimates hydraulic conditions at different water stages in a stream reach and compares them to habitat criteria to determine biological instream flow recommendations. Cloud‐based Geographic Information System features and additional tools are incorporated that augment information and aid in evaluating ecological needs. The development of the R2Cross tool enables an open‐access interface for management authorities and stakeholders to evaluate ecological needs at stream reaches. It automates the reporting process and could assist in making water management decisions about environmental protection. Although the R2Cross tool was developed for the state of Colorado, it is generalizable to other stream systems assuming similar habitat criteria.

Water Rights Analysis Package Modeling System

The water rights analysis package simulates surface water development, allocation, management, and use and performs reliability and frequency analyses of simulation results. The computer modeling system facilitates assessments of hydrologic and institutional water availability and reliability in satisfying requirements for reservoir storage, water supply diversions, environmental instream flows, and hydroelectric energy generation. Reservoir system operations for flood control can be simulated. Capabilities are also provided for tracking salinity concentrations. Basin-wide impacts of water resources development projects and management practices are modeled. The modeling system is generalized for application anywhere, with input datasets being developed for particular river systems of concern. The water availability modeling system maintained by the Texas Commission on Environmental Quality and routinely applied by the professional water management community consists of the water rights analysis package and simulation input datasets for all of the river basins of Texas. Model-users modify the input datasets as appropriate to evaluate alternative water use scenarios, development projects, and management strategies of interest. This paper explores concepts and methodologies incorporated in the water rights analysis package and other comparable modeling systems, implementation of water availability modeling in Texas, and contributions to effective water management.

Diel patterns of foraging and microhabitat use by sympatric rainbow trout and bull trout: implications for adaptive differentiation and instream flow assessment

Salmonids make flexible and adaptive trade-offs between foraging efficiency and predation risk that result in variable patterns of diel activity and habitat use. However, the following remains unclear: (1) how patterns differ among salmonid species; and (2) how this affects the interpretation of habitat suitability models that inform instream flow management. We combined snorkel observations with experimental additions of cover to investigate how predation risk, cover, and bioenergetics affect diel activity and habitat use patterns by sympatric rainbow trout (Oncorhynchus mykiss) and bull trout (Salvelinus confluentus) in the Skagit River, British Columbia, Canada. Both species foraged primarily at dusk, supporting the well-described trade-off between foraging efficiency and predation risk. However, only rainbow trout responded to cover additions, suggesting that risk tolerance and the nature of foraging-predation risk trade-offs differ between species. Diel shifts in activity and habitat use also substantially altered predictions of habitat suitability models, with potentially large consequences for flow management.

Reach‐scale stream temperature response to large wood placement

Climate change models indicate that stream temperatures within much of the Columbia River Basin will increase significantly in the next 50 years leading to inhospitable conditions for salmonid fishes in several stream reaches. Restoration measures such as riparian planting, maintaining instream flows, and large wood (LW) placement are thought to ameliorate the impacts of climate change on stream temperatures. While LW placement is known to improve habitat complexity, it is unclear whether it will also help reduce summer stream temperatures. To help understand the influence of LW placement on stream temperatures, we monitored nine interior Columbia River Basin LW projects using an extensive posttreatment study design. We mapped stream bottom temperatures, topography, and physical habitat in paired treatment (LW placement) and control reaches to compare water temperatures and cool‐water patches between reaches. We found no difference in the mean or the variance in overall reach temperatures or thalweg temperatures between treatment and control reaches. Mapping found variation in water temperatures of less than 0.5°C within reaches, making mapping of cool‐water patches impractical and further emphasized the lack of temperature differences. Our results indicate that LW placement projects in the interior Columbia River Basin do not appear to be decreasing reach‐scale summer water temperatures or creating cool water refugia for fishes. Moreover, the current configuration and implementation of LW placement projects, which typically focus on placing wood on banks and channel margins, are unlikely to ameliorate the effects of climate change on stream temperatures.

PHABSIM/SEFA Application for Minimum Flows and Levels Development in Florida

Physical Habitat Simulation System (PHABSIM) or System for Environmental Flow Analysis (SEFA) are typically used to simulate the relationship between river flow and physical habitat of various life stages of a fish species. They are a component of the Instream Flow Incremental Methodology (IFIM) and are widely used across the globe for deductive estimation of biological effects of stream flow alteration. These models have been applied at various spatial and temporal scales corresponding to the objectives of the specific applications. The objectives of this work effort are to review spatial and temporal scales of previous habitat modelling applications and to recommend a best practice approach for the application of physical habitat simulation software. Two leading software packages are considered-PHABSIM and SEFA, both are improvements of IFIM framework. Specifically, this research paper recommends best practices that can be used in environmental flows development. The review was focused on literature related to selecting species, and the time steps for developing and applying Area Weighted Suitability (AWS) vs. discharge curves used for developing environmental flows. The term AWS in SEFA replaces the original weighted usable area (WUA) in PHABSIM because it is a more accurate description of the physical meaning of the variable.

Identifying and mitigating systematic biases in fish habitat simulation modeling: Implications for estimating minimum instream flows

AbstractHabitat simulation approaches (e.g., PHABSIM) have been used to model instream flows in thousands of streams and rivers and remain the most widely implemented detailed instream flow methodology. However, recent studies suggest that conventional habitat simulation models incorporate assumptions that may systematically underestimate instream flow needs, particularly for drift‐feeding fish. These include: (i) systematic biases in velocity habitat suitability curves (HSCs) caused by territoriality where dominant individuals displace subordinate fish to lower velocity micro‐habitats at high densities, thereby inflating the fitness value of low velocities; (ii) habitat simulation models do not account for flow effects on prey flux to drift‐feeding fishes, which may decrease more rapidly with reduced flow than does available habitat; (iii) use of focal velocities to construct traditional HSCs, which systematically underestimates velocity preference within the broader foraging arena of a drift‐feeding fish, and (iv) inadvertent use of low‐velocity HSCs associated with daytime refuging behavior from predators that may underestimate the higher velocities necessary for crepuscular foraging. Collectively, these factors suggest that current and historic flow prescriptions using traditional habitat simulation methods may underestimate optimal rearing flows for salmonids and other drift‐feeding species by anywhere from 10 to 50%. This implies that traditional instream flow management may be failing to provide the intended level of protection for drift‐feeding fishes in multiple streams at landscape scales. We provide guidelines for identifying contexts where model predictions are likely to be biased and approaches for correcting them.

Best management practices for mitigating agricultural nutrient pollution in the Mun River Basin, Thailand

The Mun River in NE Thailand is one of the significant tributaries of the Lower Mekong River. Its poor river quality has been reported and agricultural activities were claimed to be major causes. This study aims to assess the best management measures appropriately responsive to the nutrient pollution in the Mun River Basin’s agricultural ecosystems. The data used for the analysis were acquired from field measurements during the 2018 wet season via satellite retrieval and secondary data collection. Linkages between land-soil datasets and hydro-water quality datasets were assessed through a canonical correlation analysis. The results suggest possible conservation measures with crop yield improvement and fertiliser cost reduction in the western basin. For the southern basin, which exhibits high sediment loading, integrated conservation measures for soil loss reduction with in-stream flow deceleration should be chosen. In the eastern basin, woody buffer strips and check dams should be prioritised. Both nutrient and sediment pollution were experienced in the middle part of the Mun River Basin and applications of low-P manure with mineral NK are recommended. Nonetheless, other soil-water conservation measures can be optionally applied to enhance the effectiveness in the watershed management.

Geospatial decision support system for ameliorating adverse impacts of irrigated agriculture on aquatic ecosystems

Tributary stream systems provide an important source of water for sustaining adjacent irrigated agricultural enterprises. Unfortunately, irrigation withdrawals, depending on the timing and amounts, can have substantial negative impacts on critical aquatic ecosystems in the tributaries. Current regulatory trends in many regions point to increased restrictions on irrigation diversions for ecosystem protection, which could lead to increased risk of shortfalls in agricultural crop production. A geospatial decision support system (geo-DSS) integrating a spatially gridded hydro-meteorological flow estimation model (HL-RDHM) with a GIS-based river basin management model (GeoMODSIM) is presented for evaluating water management alternatives for maintaining the viability of irrigated agriculture while mollifying detrimental impacts on aquatic ecosystems and maintaining environmental flow requirements. As a case study, the geo-DSS is applied to the Feliz Creek basin tributary to the Russian River of northern coastal California which is home to a thriving viticulture industry while supporting spawning habitat for endangered and threatened fish species. The geo-DSS is applied on spatial (~1 km grid size) and temporal (daily) scales that are ecologically relevant for modeling agricultural operations and water rights priorities. The geo-DSS utilizes extensive sets of hydrologic forcing data varying from dry to wet conditions to assess baseline conditions and evaluate management alternatives. Baseline model results show that with minimum bypass flow restrictions in place for instream flow protection, the cumulative effects of upstream diversions can still be significant during low flow periods, while creating substantial risk of agricultural irrigation supply shortages. The case study application demonstrates that the geo-DSS is capable of locating, sizing, and managing off-stream farm ponds receiving optimally timed diversions from adjacent streams that are necessary for maintaining agricultural water supply while complying with environmental flow requirements for sustaining aquatic ecosystems.

Monitoring Trout Response to Instream Flow

Run‐of‐river hydropower reduces streamflow between diversion and powerhouse, potentially impacting fish. Hydropower license conditions include instream flows to protect fish, but monitoring instream flow effectiveness to protect fish is rarely reported. Monitoring a trout population before construction (baseline) and during operation of a small hydropower project with instream flows for spawning and incubation, summer rearing, and winter rearing based on a Physical Habitat Simulation System in the state of Washington indicated the instream flow protected the trout. The monitoring plan included decision points based on monitoring results. Increasing or stable population trends would trigger locking in an instream flow for the remainder of the license, while declines would trigger incremental increases in the instream flow, followed by additional monitoring and decision points. Three years of monitoring following beginning of the project indicated an apparent increase in the trout population over baseline, suggesting that the instream flow was protective, triggering finalization of instream flows. An additional year of monitoring conducted after several more years of project operation was consistent with the finding of the first 3 years of operation.