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California has increasingly emphasized efforts to develop voluntary agreements (VAs) with water users as a means of achieving regulatory goals in certain watersheds. In theory, a VA can combine the protectiveness of a regulatory backstop with the creativity and flexibility of a negotiated deal to produce outcomes as good as, or better than, those achievable through strict application of regulatory requirements alone. However, reality has not always measured up to this ideal. This policy paper uses the Bay-Delta watershed as a case study to inform five principles to guide the appropriate use and evaluation of VAs.

South Korea's River Act mandates the maintenance of instream flow to support river ecosystems. This regulation has evolved from early river management practices to more advanced, systematic approaches, including the Instream Flow Incremental Methodology (IFIM). Despite these advancements, river management in South Korea, particularly in the Seomjin River Basin, continues to face numerous challenges. In this study, a three-dimensional numerical model was developed to simulate the hydrodynamic and salinity conditions of the Seomjin River Estuary. This study proposes optimal instream flows to support critical habitats for the Corbicula bivalve, which has seen a significant decline due to salinity intrusion by environmental changes. Using the Environmental Fluid Dynamics Code (EFDC), the model simulates salinity and river discharge with calibration and validation by incorporating historical data. Subsequently, this study evaluates how river discharge affects salinity in four major Corbicula habitats (Dugok, Shinbi, Mokdo, and Hwamok). Finally, we determine the minimum flow (instream flow) needed to sustain Corbicula habitats. In short, this study found that the minimum flow rates (instream flow) required to meet target salinities varied significantly across these sites and under different tidal conditions. These findings highlight the necessity of adapting river flow management practices to preserve the ecological health for Corbicula in the Seomjin River Estuary. Furthermore, this study suggests integrating an additional water supply to be used with local water management plans by suggesting short-term and long-term alternatives in order to sustain adapting river minimum flow (instream flow). [ABSTRACT FROM AUTHOR]

The article focuses on adapting generalized depth preference and flow velocity characteristics from Brown trout (Salmo trutta morpha fario) to the Minnow (Phoxinus phoxinus). The results obtained were used to model habitat suitability with 1D and 2D models. Since 1995, research on assessing aquatic habitat quality has been ongoing on 77 mountain streams in Slovakia. This assessment employs a System of Environmental Flow Analysis (SEFA), which is based on the Instream Flow Incremental Methodology (IFIM). In most sections, Brown trout occurred in representative numbers. Brown trout habitat preferences were derived and generalized, and represented by suitability curves. Minnows were present in sufficient numbers for the derivation of suitability curves only on some streams, making direct generalization from the measured data unrepresentative. The measurement results showed that Minnow has similar depth and flow rate preferences to Brown trout. Therefore, it can be assumed that it is possible to adapt the generalised suitability curves from Brown trout to Minnow. This expansion enabled us to broaden the assessment of habitat quality using the SEFA model to mountain streams that are dominated by Minnows and where there is insufficient Brown trout presence. Verification of parameter adaptation from Brown trout to Minnow was conducted in 11 sections of mountain streams. We discuss the performance of habitat quality modeling, concerning the fundamental hydraulic characteristics of streams, using both 1D and 2D models. The results of the 2D modeling are presented for a sub-mountain stream. [ABSTRACT FROM AUTHOR]

Seomijn River Basin has numerous hydraulic structures designed to satisfy water demands and mitigate future droughts. However, the increasing water demand and export to neighboring areas cause water deficits and conflicts between water users. Therefore, practical strategies to mitigate the potential damage from climate change are essential. In this study, we aimed to propose practical strategies under climate change by examining the future water security of the Seomjin River Basin under five different water allocation scenarios referenced from the practical policies of various countries. Future climate models determined based on extreme precipitation indices of the ETCCDI were used to investigate their impact on water security, which was evaluated using unmet demand; demand coverage; reliability, resilience, and vulnerability; and aggregation index metrics. We found that prioritizing domestic and industrial water use is the optimal water security strategy, and unconditional allocation of instream flow can cause a significant water deficit for other water uses. However, prioritizing all water uses equally also proved effective under some conditions. Thus, our study highlights the importance of adaptive management and suggests that the optimal water allocation strategy lies in its flexibility in response to varying circumstances. [ABSTRACT FROM AUTHOR]

Abstract The literature has explored various methods for assessing minimum environmental flow. Implementing holistic approaches proves to be prohibitively expensive and impractical for many small and medium projects. Hence, desktop and cost-effective methods are commonly employed without an integrated decision-making system to justify the assessed values. This study introduces a systematic decision-making framework aimed at selecting the most suitable method for assessing the actual needs of river habitats. Employing a fuzzy technique known as the Order Preference Similarity to the Ideal Solution (FTOPSIS), the study considers factors such as physical, thermal, and dissolved oxygen habitat suitability, maximum habitat area, and water demand loss function to determine the most appropriate method among established ones, including the Tennant method, flow duration curve analysis method, wetted perimeter method, and physical habitat simulation method. The results prioritize physical habitat simulation, wetted perimeter by slope method, and flow indices of 70%, 75%, and 80% by flow duration curve analysis method as the optimal approaches for assessing minimum environmental flow. This proposed decision-making system offers a viable platform to explore the applicability of existing cost-effective methods for assessing minimum environmental flow. It also serves as an effective mechanism for reducing negotiations among stakeholders by comprehensively considering all relevant aspects in the environmental management of river ecosystem requirements.

The literature has explored various methods for assessing minimum environmental flow. Implementing holistic approaches proves to be prohibitively expensive and impractical for many small and medium projects. Hence, desktop and cost-effective methods are commonly employed without an integrated decision-making system to justify the assessed values. This study introduces a systematic decision-making framework aimed at selecting the most suitable method for assessing the actual needs of river habitats. Employing a fuzzy technique known as the Order Preference Similarity to the Ideal Solution (FTOPSIS), the study considers factors such as physical, thermal, and dissolved oxygen habitat suitability, maximum habitat area, and water demand loss function to determine the most appropriate method among established ones, including the Tennant method, flow duration curve analysis method, wetted perimeter method, and physical habitat simulation method. The results prioritize physical habitat simulation, wetted perimeter by slope method, and flow indices of 70%, 75%, and 80% by flow duration curve analysis method as the optimal approaches for assessing minimum environmental flow. This proposed decision-making system offers a viable platform to explore the applicability of existing cost-effective methods for assessing minimum environmental flow. It also serves as an effective mechanism for reducing negotiations among stakeholders by comprehensively considering all relevant aspects in the environmental management of river ecosystem requirements. [ABSTRACT FROM AUTHOR]

The Korean Peninsula's mountainous terrain poses challenges to effective water resource management. Notably, two significant river basins, North Han River and Imjin River basins, are essentially shared rivers originating in North Korea. After the construction of various dams in North Korea, billions of tons per year of water annually decreased from the upper reaches of these rivers of North Korea to South Korea. This study conducted an impact analysis on two major river basins affected by dam operations in North Korea. Both before and after the Imnam Dam operation, significant reduction (27.7%) in the average monthly inflow was observed, and the total release of the Hwacheon Dam in South Korea decreased by 40.2%. The analysis of instream flow indicated that the operation of dams in North Korea had a substantial impact on fulfilling instream flow requirements for dams located in North Han River and Imjin River basins. To ensure instream flow, this study proposed two plans. The first plan involved the utilization of existing dams in the North Han River basin, while the second plan suggested connecting the dams in North Korea, taking into account the shared rivers. HIGHLIGHTS The effects of streamflow fluctuation resulting from two major dams’ operations in North Korea was analyzed.; Whether all dams in South Korea released to maintain the instream flow was examined.; Two plans to ensure the instream flow were proposed. The first plan involved the existing dams’ utilization in South Korea and another plan revealed the connection of the dams in North Korea, considering the shared rivers.;

Dams and reservoirs are often needed to provide environmental water and maintain suitable water temperatures for downstream ecosystems. Here, we evaluate if water allocated to the environment, with storage to manage it, might allow environmental water to more reliably meet ecosystem objectives than a proportion of natural flow. We use a priority-based water balance operations model and a reservoir temperature model to evaluate 1) pass-through of a portion of reservoir inflow versus 2) allocating a portion of storage capacity and inflow for downstream flow and stream temperature objectives. We compare trade-offs to other senior and junior priority water demands. In many months, pass-through flows exceed the volumes needed to meet environmental demands. Storage provides the ability to manage release timing to use water efficiently for environmental benefit, with a co-benefit of increasing reservoir storage to protect cold-water at depth in the reservoir. Allocating a proportion of water and storage for the environment allows water to efficiently meet environmental needs. This reduces inefficiencies caused by instream flows exceeding environmental demands. [ABSTRACT FROM AUTHOR]

The ability to reallocate water to higher‐value uses during drought is an increasingly important "soft‐path" tool for managing water resources in an uncertain future. In most of the Western United States, state‐level water market institutions that enable reallocation also impose substantial transaction costs on market participants related to regulatory approval and litigation. These transaction costs can be prohibitive for many participants in terms of both costs and lengthy approval periods, limiting transfers and reducing allocation efficiency, particularly during drought crises periods. This manuscript describes a mechanism to reduce transaction costs by adapting an existing form of informal leases to facilitate quicker and less expensive transfers among market participants. Instead of navigating the formal approval process to lease a water right, informal leases are financial contracts for conservation that enable more junior holders of existing rights to divert water during drought, thereby allowing the formal transfer approval process to be bypassed. The informal leasing approach is tested in the Upper Colorado River Basin, where drought and institutional barriers to transfers lead to frequent shortages for urban rights holders along Colorado's Front Range. Informal leases are facilitated via option contracts that include adaptive triggers and that define volumes of additional, compensatory, releases designed to mitigate impacts to instream flows and third parties. Results suggest that more rapid reallocation of water via informal leases could have resulted in up to $222 million in additional benefits for urban rights holders during the historical period 1950–2013. Plain Language Summary: In much of the developed world, there is little ability to sustainably manage water resources by building more dams or digging new wells. Water stressed regions are increasingly adapting to droughts through agreements to conserve or reallocate water between members of the community. In some places, markets make this easier by allowing users to buy and sell water. However, in most of the Western U.S., the legal system that approves these transactions makes them very costly and time consuming, reducing the benefits from trade. In particular, it is very hard to buy and sell short‐term leases. Here, we propose a new type of leasing contract, "informal leases," that avoid the legal system by relying on contractual agreements between water users. Instead of buying water via the legal system water users pay other users to conserve, coordinated through simple index contracts. When these contracts are designed correctly, they can perfectly recreate the effect of a formal water sale, for a fraction of the price. In this manuscript, we show how contracts for informal leases can be designed and evaluated, creating savings for water buyers/sellers, additional revenue for their neighbors, and a win/win response to environmental stress (for everyone except the lawyers). Key Points: Transaction costs related to regulatory approval are a significant impediment to water market leases in the Western United StatesInformal leases enable rapid short‐term water reallocation during drought while reducing transaction costsThe State of Colorado could have accrued $222 million in benefits using informal leases to reallocate water from irrigators to urban users [ABSTRACT FROM AUTHOR]

In the face of a changing climate and increasing human demand for water, an understanding of habitat preference has become critical for managing wild fish populations and projecting potential changes in habitat and populations. Two approaches to Physical Habitat Simulation (PHABSIM) modeling of coastal cutthroat trout Oncorhynchus clarkii clarkii spawning habitat were compared by modeling a reach, consisting of eight transects covering a pool and upstream and downstream riffles, of a small Puget Sound stream with two sets of habitat variables. The reach contained a cluster of redds 2 years in a row, assumed to be an indication of preferred spawning habitat and was located in the area of maximum spawning in the watershed, based on multiple years of redd surveys. Two PHABSIM instream flow models of the study site, one based on standard microhabitat (depth [D], velocity [V], and substrate [S]) suitabilities and the other based on D, V, and channel unit (CU) suitabilities, were developed and compared for their relative ability to correctly predict coastal cutthroat trout spawning habitat selection at the redd cluster within the PHABSIM study site. One approach was the standard use of habitat suitability criteria (HSC) for D, V, and S to indicate spawning habitat quality. The alternate approach was to replace substrate HSC with CU index HSC that incorporated dominant substrate particle diameter, CU (riffle, deep and shallow pool tail, pool body, deep and shallow pool edge, cascade, waterfall, and terrestrial), where deep and shallow units were based on relative residual depth (RRD), size of CU relative to channel width, and position within CU. Spawning habitat quality was calculated for each transect as weighted usable width with the standard HSC metrics (WUWs) as well as the modified CU index (WUWm). WUWm at the transects bracketing the redd cluster exceeded WUWm at the remaining six transects and was outside the 95% confidence interval for WUWm at the remaining transects. In contrast, WUWs varied less between the redd cluster and the remainder of the transects, suggesting the CU index better reflected spawning habitat quality than substrate. Incorporation of elevation relative to SZF addressed vulnerability to declining flow during incubation. Both models resulted in maximum WUA within the range of discharges that coincided with the majority of fresh cutthroat trout redds in Skookum Creek. [ABSTRACT FROM AUTHOR]

Aligning water supply with demand is a challenge, particularly in areas with large seasonal variation in precipitation and those dominated by winter precipitation. Climate change is expected to exacerbate this challenge, increasing the need for long‐term planning. Long‐term projections of water supply and demand that can aid planning are mostly published as agency reports, which are directly relevant to decision‐making but less likely to inform future research. We present 20‐year water supply and demand projections for the Columbia River, produced in partnership with the Washington State Dept. of Ecology. This effort includes integrated modeling of future surface water supply and agricultural demand by 2040 and analyses of future groundwater trends, residential demand, instream flow deficits, and curtailment. We found that shifting timing in water supply could leave many eastern Washington watersheds unable to meet late‐season out‐of‐stream demands. Increasing agricultural or residential demands in watersheds could exacerbate these late‐season vulnerabilities, and curtailments could become more common for rivers with federal or state instream flow rules. Groundwater trends are mostly declining, leaving watersheds more vulnerable to surface water supply or demand changes. Both our modeling framework and agency partnership can serve as an example for other long‐term efforts that aim to provide insights for water management in a changing climate elsewhere around the world. [ABSTRACT FROM AUTHOR]

Bioenergetics models produce quantitative flow‐ecology relationships that summarize changes in habitat and food resources from altered flows. We used a drift‐foraging bioenergetics model to quantify the net rate of energetic intake (NREI) for trout above and below a water diversion. NREI is reduced by >95% below the water diversion in July–September, when up to 98% of unimpaired flows are diverted. We then used a risk‐based approach to estimate the maximum diversion rate, expressed as a percentage of unimpaired flow, that would produce NREI values that are not significantly lower than values under unimpaired flows throughout a 62‐year period. NREI decreased with increased precent‐of‐flow diversion rates in low‐flow months (July–September). Diversion rates of 16% in July and 9% in August and September would maintain NREI within the range of unimpaired flow conditions. In higher flow months, May–June, increasing diversions brought estimated instream flows closer to the peak NREI flow, leading to the assessment that increased diversions would increase NREI. Bioenergetic models can be used to develop protective flow rates at times of the year when fish growth and production would be high under unimpaired flows, which often coincides with when water is diverted. Our study is the first to develop protective percent‐of‐flow diversion rates for holistic flow management using a quantitative process‐based and fish‐centric ecological metric. [ABSTRACT FROM AUTHOR]

A thorough understanding of the ecological impacts behind the hydrologic alteration is still insufficient and hinders the watershed management. Here, we used eco-flow indicators, multiple hydrological indicators, and fluvial biodiversity to investigate the ecological flow in different temporal scales. The case study in the Han River shows a decrease in high flows contributed to the decrease in eco-surplus and increase in eco-deficit in summer and autumn, while the decrease in eco-deficit can be attributed to the change of low flow in spring. An integrated hydrologic alteration was over 48% degree and was under moderate ecological risk degree in impact period I, while DHRAM scores showed the Huangzhuang station faced a high ecological risk degree in impact period II. The decrease (increase) in total seasonal eco-surplus (eco-deficit) was identified after alteration with the change in seasonal eco-flow indicators contributions. Shannon index showed a decreasing trend, indicating the degradation of fluvial biodiversity in the Han River basin. Eco-flow indicators such as eco-surplus and eco-deficit are in strong relationships with 32 hydrological indicators and can be accepted for ecohydrological alterations at multiple temporal scales. This study deepens the understanding of ecological responses to hydrologic alteration, which may provide references for water resources management and ecological security maintenance. HIGHLIGHTS Quantitative evaluation of ecological flows considering precipitation and reservoir factors.; Unveil effects of reservoirs on flow regimes in the Han River.; Comprehensive evaluation of ecological responses to hydrological alterations.; Scientific foundation for water resources management in the Han River.;

Instream flows are vital to the ecology of riverine and riparian systems. The influence of watershed characteristics on these systems is helpful in developing landscape policies to maintain these flows. Watershed characteristics like precipitation, forest cover, impervious cover, soil drainage, and slope affect baseflows. Spatial analysis using GIS and nonlinear regression analysis is used to analyze spatial and temporal information from gauged watersheds in Massachusetts to quantify the relationship between baseflows and watershed metrics. The marginal functions of landscape factors that reflect changes in baseflow are quantified. This information is then applied to watershed policy toward improving base flows. The interactions of three fixed attributes, soil drainage, rainfall incidence, and slope, are analyzed for the manageable landscape attributes of impervious and forest cover. Developing watershed policy to protect baseflows involves evaluating the complex interactions and functional relationships between these landscape factors and their use in watershed conservation planning. [ABSTRACT FROM AUTHOR]

With the development of human society, the balance between the minimum ecological instream flow requirement (MEIFR), which is an essential part of the ecological water demand in arid areas, and anthropogenic water depletion has received increasing attention. However, due to the lack of hydrological station data and river information on arid basins, previous researchers usually considered only the individual ecological water demand of rivers, lakes, or oases. To address this issue, a new method that combines river hydraulic parameters and the wet circumference obtained by an unmanned aerial vehicle (UAV) and remote sensing hydrological station (RSHS) technologies was applied to obtain the MEIFR and, then, systematically and quantitatively explore the balance from the perspective of the entire basin of Aiding Lake from 1990 to 2022, which is the lowest point of Chinese terrestrial territory. The results showed the following: (1) since 1990, the discharge of the seven rivers in the study area increased by 1–6%, and the MEIFR of these rivers increased by 15–100%; both quantities decreased by 3–5% from the upper to the lower reaches of the basin; (2) the surface area and water level of Aiding Lake decreased by 5% and 14%, respectively, but the MEIFR first decreased by 25% from 1990 to 2013 and, then, increased by 66.7% from 2013 to 2022; and (3) from 2011 to 2022, the MEIFR and anthropogenic water depletion exhibited a balance. Against the background of climate change, this research revealed that the MEIFR of the rivers in the Aiding Lake Basin have shown an upward trend over the past 30 years and quantitatively determined the above balance relationship and the period of its occurrence. This study supplied a method that could provide guidance for water resource management by decision-makers at a global level, thus helping achieve the sustainable development goals (SDGs). [ABSTRACT FROM AUTHOR]

The article discusses the monitoring of the effects of run-of-river (RoR) projects on resident rainbow trout in southwestern British Columbia. Topics include criticisms related to experimental design and the inferences drawn, as well as the caution needed when extrapolating these findings to other RoR projects in similar conditions.

Channel dimensions (width and depth) at varying flows influence a host of instream ecological processes, as well as habitat and biotic features; they are a major consideration in stream habitat restoration and instream flow assessments. Models of widths and depths are often used to assess climate change vulnerability, develop endangered species recovery plans, and model water quality. However, development and application of such models require specific skillsets and resources. To facilitate acquisition of such estimates, we created a dataset of modeled channel dimensions for perennial stream segments across the conterminous United States. We used random forest models to predict wetted width, thalweg depth, bankfull width, and bankfull depth from several thousand field measurements of the National Rivers and Streams Assessment. Observed channel widths varied from <5 to >2000 m and depths varied from <2 to >125 m. Metrics of watershed area, runoff, slope, land use, and more were used as model predictors. The models had high pseudo R2 values (0.70–0.91) and median absolute errors within ±6% to ±21% of the interquartile range of measured values across 10 stream orders. Predicted channel dimensions can be joined to 1.1 million stream segments of the 1:100 K resolution National Hydrography Dataset Plus (version 2.1). These predictions, combined with a rapidly growing body of nationally available data, will further enhance our ability to study and protect aquatic resources. [ABSTRACT FROM AUTHOR]

The degree of success of river water diversion planning decisions is affected by uncertain environmental conditions. The adaptive water management framework incorporates this uncertainty at all stages of management. While the most effective form of adaptive management requires experimental comparison of practices, the use of optimization modeling is convenient for conducting exploratory simulations to evaluate the spatiotemporal implications of current water diversion management decisions under future environmental changes. We demonstrate such an explorative modeling approach by assessing river water availability for diversion in a river basin in Northern Spain under two future environmental scenarios that combine climate and land use change. An evolutionary optimization method is applied to identify and reduce trade-offs with Supporting Ecosystem Services linked to environmental flow requirements for relevant local freshwater species. The results show that seasonal shifts and spatial heterogeneity of diversion volumes are the main challenges for the future diversion management of the Pas River. Basin-scale diversion management should take into account the seasonal planning horizon and the setting of tailored diversion targets at the local-level to promote the implementation of adaptive management. The presented assessment can help with strategic placement of diversion points and timing of withdrawals, but it also provides deeper insight into how optimisation can support decision-making in managing water diversion under uncertain future environmental conditions. [ABSTRACT FROM AUTHOR]

Ecological flow (E-flow) determination is an essential component of stream management and the preservation of aquatic ecosystems within a watershed. E-flow should be determined while considering the overall status of the watershed, including the hydrological cycle, hydraulic facility operation, and stream ecology. The purpose of this study is to determine E-flow by considering watershed status through coupled modeling with SWAT and PHABSIM. SWAT was calibrated to ensure reliability when coupling the two models, using observed data that included streamflow and dam inflows. The calibration result of SWAT showed that the averages of R2, NSE, and RMSE were 0.62, 0.57, and 1.68 mm/day, respectively, showing satisfactory results. Flow duration analysis using the SWAT results was performed to apply to discharge boundary conditions for PHABSIM. The averages of Q185 (mid-range flows) and Q275 (dry conditions) were suitable to simulate fish habitat. The habitat suitability index derived through a fish survey was applied to PHABSIM to estimate E-flow. E-flow was estimated at 20.0 m3/s using the coupled model and compared with the notified instream flow by the Ministry of Environment. The results demonstrate a high level of applicability for the coupled modeling approach between the watershed and physical habitat simulation models. Our attempt at coupled modeling can be utilized to determine E-flow considering the watershed status. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Water Resources Journal / Revue Canadienne des Ressources Hydriques is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper discusses why and how to use ecologically appropriate spatial resolutions (e.g., cell size or range of cell sizes) when modeling instream flow effects on aquatic animals. Resolution is important because relations between habitat and animal habitat use vary with spatial resolution, and different habitat variables may best predict habitat use at different resolutions. Using appropriate resolutions consistently would bring clarity and coherence to how we quantify and model habitat characteristics and habitat use by fish, facilitate the use of standard and more credible measures of habitat preference, incorporate more fisheries knowledge to improve models for different kinds of fish, and avoid well‐known (and perhaps unknown) biases. Doing so involves describing habitat, and habitat use by fish, with spatially explicit measures with clear resolutions; using the same resolution for physical habitat and fish habitat use; selecting that resolution for ecological reasons; and using habitat variables and fish observation methods appropriate for the resolution. The choice of resolution considers factors such as how much space fish use for specific activities and the size of important habitat patches. For drift‐feeders, cell sizes and fish habitat use observations should use a resolution no smaller than feeding territories. Piscivores typically hunt over large areas so should be modeled with larger habitat units. Models of small and less‐mobile organisms (e.g., benthic invertivores) may need fine resolutions to capture the small areas of unusual habitat they depend on. Because of such differences, instream flow studies (like any spatial ecology exercise) should clearly state what resolution(s) they use and why. [ABSTRACT FROM AUTHOR]

Conservation in working landscapes is an important aspect of stream restoration. Landowners with agricultural water rights are increasingly adding instream flow as a beneficial use of their allocated water. However, stream restoration projects commonly focus on the quantity of water dedicated to the environment and overlook water quality. For cold-water ecosystems, the preservation of natural thermal regimes is a key to conservation efforts in the face of a changing climate. This study explored the effects of increasing stream flow using alternative water sources (e.g., instream runoff versus offchannel springs) to enhance cold-water stream habitat on a working cattle ranch. Using empirical data to create a steady-state stream flow and water temperature model, we evaluated temperature benefits and management trade-offs for ecological and agricultural water use. The modeled results showed that the source of water and the method used to deliver water to the channel affected the quality and extent of cold-water habitat. Offchannel spring water cooled 7-day average maximum temperatures and 7-day average mean temperatures by as much as 3.7°C and 2.9°C, respectively, but only when potential offchannel aquatic habitat was sacrificed for mainstem habitat. When offchannel, spring-fed habitat was provided, the value of spring water to the main channel decreased. Our findings suggest that source water thermal quality is of paramount importance for enhancing ecosystem function and improving cold-water habitat in working landscapes. In addition, the restoration of a historic spring channel may provide added ecosystem benefits by enhancing aquatic habitat for cold-water species. In the western United States, understanding the best possible uses for high-quality cold-water sources may provide the greatest benefits to the environment and adjacent working landscapes. Whereas water purchases and leases tend to focus on water quantity, this study could direct such investments toward higher value sources for the environment. In places like California, where drought has resulted in water right curtailments for agricultural diverters, understanding the best uses for high quality cold water compared with other sources can provide the greatest benefits to both agriculture and the environment. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Ganga River ecosystem is under severe anthropogenic stress. Flow regulations through structural barriers alter the geomorphic and hydraulic geometry of riverine habitats. Determining the ecological health of river habitats under the contemporary modification is detrimental to its restoration and management. This study evaluates reach averaged hydraulic habitat of the endangered Ganga River dolphin (Platanista gangetica) in a stretch between Bijnor and Narora barrages. We consider an optimal minimum flow depth as the determining factor of habitat suitability. Field measurement of the hydraulic geometry and flow characteristics show that the optimal flow depth is available in the study reach during the monsoon period, while in the pre‐monsoon, the minimum depth is present only in the reach upstream to Narora barrage. We use a geomorphic instream flow tool (GIFT) and satellite altimeter water level data to simulate reach averaged hydraulic habitat in varying flow conditions in area upstream of Narora barrage. We observe that to maintain the minimum flow depth which supports the dolphin habitat in the study reach, an optimal discharge of about >280 m3s−1 is essential. Furthermore, we develop a water‐level (altimeter) and discharge (simulated from GIFT) rating curve for the study reach. It can be used to get a first‐order estimate of discharge for a given water level or vice versa. This study indicates that the altimetry datasets are good precursors for estimating averaged hydraulic habitat of rivers in the data‐scarce regions. The application of altimeter data can be a boon in the effective management of river habitat health over a reach scale. [ABSTRACT FROM AUTHOR]

Low streamflows can increase vulnerability to warming, impacting coldwater fish. Water managers need tools to quantify these impacts and predict future water temperatures. Contrary to most statistical models' assumptions, many seasonally changing factors (e.g., water sources and solar radiation) cause relationships between flow and water temperature to vary throughout the year. Using 21 yr of air temperature and flow data, we modeled daily water temperatures in California's snowmelt‐driven Scott River where agricultural diversions consume most summer surface flows. We used generalized additive models to test time‐varying and nonlinear effects of flow on water temperatures. Models that represented seasonally varying flow effects with intermediate complexity outperformed simpler models assuming constant relationships between water temperature and flow. Cross‐validation error of the selected model was ≤1.2°C. Flow variation had stronger effects on water temperatures in April–July than in other months. We applied the model to predict effects of instream flow scenarios proposed by regulatory agencies. Relative to historic conditions, the higher instream flow scenario would reduce annual maximum temperature from 25.2° to 24.1°C, reduce annual exceedances of 22°C (a cumulative thermal stress metric) from 106 to 51 degree‐days, and delay onset of water temperatures >22°C during some drought years. Testing the same modeling approach at nine additional sites showed similar accuracy and flow effects. These methods can be applied to streams with long‐term flow and water temperature records to fill data gaps, identify periods of flow influence, and predict temperatures under flow management scenarios. Plain Language Summary: Warm water temperatures threaten culturally and economically important salmon in Pacific Northwest Rivers, causing chronic stress and direct mortality. Climate change and agricultural water use have reduced summer river flows in recent decades, intensifying water scarcity. Years with deep mountain snowpack and resulting high groundwater levels extend the high flow season and keep water temperatures cool through the end of July, whereas in drought years the river warms sooner. We used 21 yr of river flow and air temperature data from the Scott River, California, to create computer models that simulate water temperatures. Our models allow the effect of flow on water temperatures to vary by season (i.e., stronger cooling effects in spring and summer), improving accuracy of the simulated temperatures. We used the Scott River model to simulate water temperatures under two alternative flow scenarios considered in local water management plans. Our simulations indicate that relative to current conditions, the higher flow scenario would lower the summers' highest temperatures and decrease the number of days that river temperatures exceed a biological threshold. Testing the same modeling approach at nine additional Klamath Basin sites showed similar accuracy and flow effects. Our model is freely available for public use. Key Points: In this snowmelt and groundwater‐influenced river, water temperatures stayed cool later into summer in high‐flow years than low‐flow yearsStatistical water temperature model predictions became more accurate when the influence of river flow was allowed to vary seasonallyThese accessible models can be applied to other rivers or streams with daily, long‐term flow and water temperature records [ABSTRACT FROM AUTHOR]

The present study proposes an integrated framework to optimize environmental flow of the multireservoir systems in which a rainfall-runoff model and a novel form of the reservoir operation optimization are linked. Soil and water assessment tool was utilized as the rainfall-runoff model to forecast inflow of the reservoir. Then, outputs of the rainfall-runoff model were used in the optimization model. Ideal environmental flow regime was considered as the target of the environmental flow in the optimization model based on the outputs of the instream flow incremental methodology proposed by the previous studies in the case study. Moreover, minimum environmental flow regime in the optimization model was defined using penalty function method. Evolutionary algorithms were utilized to optimize the reservoir operation. Then, the performance of the algorithms was assessed by different measurement indices. Finally, the fuzzy technique of order preference similarity to the ideal solution was applied to select the best algorithm. Based on the results in the case study, the proposed framework is properly able to optimize environmental flow regime in the multireservoir system. Measuring the performance of the optimization system indicated that average reliability index is 70% for supplying environmental flow. Moreover, the optimization system is able to minimize storage loss and water supply loss simultaneously. The particle swarm optimization is the best algorithm to optimize environmental flow regime in the case study. Using the proposed method is recommendable to minimize negotiations between stakeholders and environmental managers that might provide a fair balance between environmental requirements and water demand. [ABSTRACT FROM AUTHOR]

Integrated assessment models (IAMs) capture synergies between human development and natural ecosystems that have important implications for the food-energy-water (FEW) nexus. However, their lack of fine-scale representation of water regulatory structure and landscape heterogeneity impedes their application to FEW impact studies in water-limited basins. To address this limitation, we developed a framework for studying effects of global change on regional outcomes for food crops, bioenergy, hydropower, and instream flows. We applied the new methodology to the Columbia River Basin (CRB) as a case study. The framework uses the Demeter land-use and land-cover change (LULCC) downscaling tool, which we updated so that water rights are spatially integrated in the land allocation process. We downscaled two LULCC scenarios (SSP2-RCP 4.5 and SSP5-RCP 8.5) under three levels of irrigation expansion: no expansion (historical extent), moderate expansion (all land presently authorized by a water right is irrigated), and maximum expansion (new water rights are granted to cover all irrigable land). The downscaled scenarios were evaluated using a hydrology-cropping systems model and a reservoir model coupled in a linear fashion to quantify changes in food and bioenergy crop production, hydropower generation, and availability of instream flows for fish. The net changes in each sector were partitioned among climate, land use, and irrigation-expansion effects. We found that climate change alone resulted in approximately 50% greater production of switchgrass for bioenergy and 20% greater instream flow deficits. In the irrigation-expansion scenarios, the combination of climate change and greater irrigated extent increased switchgrass production by 76% to 256% at the cost of 42% to 165% greater instream flow deficits and 0% to 8% less hydropower generation. Therefore, while irrigation expansion increased bioenergy crop productivity, it also exacerbated seasonal water shortages, especially for instream use. This paper provides a general framework for assessing benchmark scenarios of global LULCC in terms of their regional FEW subsystem outcomes.

Tropical island streams are heavily impacted by water withdrawals to the detriment of native ecosystems. Freshwater fauna in the tropics often exhibit diadromous life‐history strategies, requiring hydrologic connectivity between upstream and nearshore habitats. During some or most of the year, this connectivity is generally lost at points of water withdrawal, typically constructed as a low‐head dam diversion. In 2010, instream flow standards (i.e., minimum environmental flows) were established for streams in East Maui, Hawai'i, which led to the partial restoration of flow in certain streams. In 2016, flow in several of these streams was then fully restored. We surveyed 10 streams before (2012) and after (2017) varying degrees of flow restoration (none, partial, full) to explore the short‐term consequences of reestablishing natural streamflow for the migratory fauna of high‐elevation tropical streams. Using visual point‐quadrat surveys, we quantified density and habitat usage of the endemic atyid shrimp (Atyoida bisulcata) and sampled A. bisulcata populations using seine‐netting to assess size frequency, sex ratio, percent ovigerous (egg bearing) females, and percent juveniles. In streams with full flow restoration, shrimp density increased in 2017 compared to 2012, while mean body size declined, suggesting increased recruitment following restoration. By contrast, streams that did not experience any flow restoration had similar shrimp densities and body sizes across years. Further, the male: female ratio declined from 18:1 in 2012 to 6.5:1 in 2017, suggesting an increase in reproductive potential of the population. Our results demonstrate that freshwater ecosystems upstream of diversion structures may respond rapidly to the restoration of hydrologic connectivity via increased recruitment of amphidromous species. [ABSTRACT FROM AUTHOR]

The article addresses practical needs for improved impact assessment and decision making, especially in respect to better use of scoping as an essential start to any impact assessment. It discusses that Scoping includes methods for identifying and prioritising the key issues and focuses impact assessments on addressing them and considers impact assessment practice in South Africa where scoping is defined by legislation as a requirement for any impact assessment.

Understanding habitat availability and use patterns are essential in developing comprehensive conservation strategies for focal species. Studies on amphibian larval habitat use are limited, especially from modified habitats. We investigated the habitat availability and use patterns of overwintering tadpoles of the Nanorana frog in an anthropogenically modified stream in the western Himalaya. Habitat was assessed in terms of depth, velocity, substrate type, and instream cover. We quantified the microhabitat preference of the tadpoles to develop habitat suitability criteria (HSC) curves, the biological component of habitat simulation tools used in instream flow management. We analyzed the data covering winter and post‐winter seasons using cumulative link mixed models to understand the influence of check dams and seasons on the hydraulic properties of microhabitats used by the tadpoles. We confirm the influence of check dam and season on velocity and the influence of season on depth used by the tadpoles. Based on this, we generated HSCs for tadpoles occurring in natural and modified pools during both seasons. We recommend intermediate water depths (30–60 cm) during the low flow season to sustain the tadpole population in the study stream and other required habitat features. The study underlines the importance of spatial and temporal variation in the habitat suitability for Nanorana tadpoles. These HSCs can be used in hydrological models for estimating the minimum ecological flow for overwintering tadpoles in the study area. A large‐scale study based on the recommendations can lead to a better conservation plan in light of altered streamflow in the western Himalaya region. [ABSTRACT FROM AUTHOR]

For riparian woodlands, occasional floods provide geomorphic disturbance that creates barren colonization sites, and river stage patterns that enable seedling establishment. To investigate impacts from river damming and instream flow regulation on these processes, we studied the lower Red Deer River in the semi‐arid region of Alberta, Canada. Dickson Dam was implemented in 1983 and although major flood peaks in June 2005 and June 2013 were attenuated by about one‐quarter, substantial seedling establishment of plains cottonwoods (Populus deltoides) was observed. Cross‐sectional transects in 2014 and 2015 revealed the reproductively mature cottonwood band from 2005, while the 2013 colonization was limited to low elevations of 0.3–1.3 m above the base river stage. Seedling numbers and the elevational ranges were probably reduced by abrupt (>4 cm/day) river stage reductions in July 2005 and in July 2013. In addition to direct seedling establishment on barren sandbars, we observed "coupled colonization" with cottonwood recruitment within sparse patches of sandbar willows (Salix exigua). The flood‐tolerant willows stabilize the bars and increase aggradation through sediment trapping. Thus, cottonwood colonization persisted after damming, indicating that the pattern of downstream flow regulation was important, rather than damming per se. To sustain riparian recruitment along regulated rivers in dry regions, we recommend: (1) that floods be allowed as feasible, (2) higher river stages during seed dispersal, (3) flow ramping (gradual summer recession) for seedling survival, (4) sufficient growing season flows to avoid drought‐induced mortality, and (5) that willows be encouraged as well as cottonwoods. [ABSTRACT FROM AUTHOR]

A wall-resolved compressible large-eddy simulation is performed on a linear compressor cascade with tip gap to investigate the tip-leakage noise sources. The cascade is composed of eight 4%-thick modified circular-arc blades with a 254 mm chord and a 235 mm spacing. The chord-based Reynolds number is 3.88×105, and the Mach number is 0.07. The gap considered in this study is 4.0 mm (1.6% chord). An aerodynamic analysis of the tip-leakage flow coupled with a Ffowcs-Williams and Hawkings analogy to compute the noise in the far field allows identifying the main tip-noise mechanisms. The acoustic contribution of the tip-leakage flow is highlighted by comparison with the trailing-edge noise contribution obtained with a 25 mm slice configuration at midspan without tip gap. This small-span configuration is also simulated using large-eddy simulation and allows computing the blade trailing-edge noise. A dynamic mode decomposition performed on the full configuration close to the tip highlights the main noise source, located around 75% chord with a propagation frequency between 5 and 6 kHz. The acoustic waves propagate mostly downstream of the cascade and on the pressure side. This study provides the first high-fidelity wall-resolved compressible simulation of a linear compressor cascade comprising a comprehensive investigation of the tip-leakage noise sources, which is a necessary first step toward fan tip-noise prediction. [ABSTRACT FROM AUTHOR]

Models developed to capture underlying river processes over long historical periods and varying hydrologic conditions provide confidence for subsequent forecasting applications. However, many areas lack the weather data needed to develop process‐based models over these long periods. Climate reanalysis data sets (CRDs) are increasingly used as surrogates for historical meteorology, but their use in river temperature models is still relatively new and untested. Testing of temperature models using CRDs in rivers experiencing a range of instream flow, weather, and topographic conditions is needed to validate the application of these data sets. Focusing on the ERA5‐Land CRD, correction methods that relate weather variables and elevation were tested using weather stations surrounding and adjacent to the Colorado River in Grand Canyon. Our findings show that elevation corrections improved air temperature and relative humidity, but negatively impacted wind speed estimates. Two‐year river temperature model simulations in a 387‐km segment of the Colorado River in Grand Canyon and a 576‐km segment of the Green River showed that using elevation‐corrected ERA5‐Land inputs produced lower mean errors at downstream river locations when compared to predictions using elevation‐corrected ground‐based inputs. Better river temperature predictions when using ERA5‐Land are attributed to the ability to represent spatial variability in weather conditions over these large areas. These promising results persisted when spatially coarsened ERA5‐Land inputs were used. This study highlights the importance of having spatially varying weather information, even at relatively coarse resolutions, when modeling physical processes over large spatial scales and suggests confidence in using CRDs for obtaining this information. Key Points: Elevation corrections improve the representation of ground‐based and reanalysis weather data in topographically complex areasElevation corrected ERA5‐Land weather can be used to predict river temperature over large time and space domains in data sparse regionsCoarsening the spatial resolution of ERA5‐Land had nominal impacts on river temperature predictions [ABSTRACT FROM AUTHOR]

To evaluate the consequences of declining summer discharge for drift abundance and energy flux to drift-feeding fish, we collected monthly drift samples from April to September in three small British Columbia salmonid streams. We complemented this with an analysis of published studies to test for broader-scale effects of summer low flows across multiple streams. This analysis indicated that a reduction in drift biomass concentration (mg m−3) over the summer low-flow recession appears to be typical in most temperate and Mediterranean climate streams. However, there was also some evidence for a behavioral increase in drift at flows below 5% of mean annual discharge (MAD), although this threshold should be treated as provisional because of low sample size. A general decline in drift biomass per m3 over the summer low-flow recession suggests that energy flow and therefore habitat capacity for drift-feeding salmonids likely decreases much more quickly than discharge, or with predictions from traditional instream flow models that only consider flow-related changes in available physical habitat and neglect changes in prey abundance. [ABSTRACT FROM AUTHOR]

In the present study, Indicator of Hydrological Alteration (IHA) tool is used to calculate the Hydrologic Alteration (HA) along the middle and lower Krishna River Basin. 33 ecological parameters are evaluated to understand the impact of the dams on the downstream of the ecological instream flow. This study focuses on assessing HA through dam impact periods by differentiating and comparing the discharge data into pre- and post-dam impact periods. Therefore, the data affected by the climate variability are eliminated. The obtained results show that the impact of the Nagarjuna Sagar dam is high with an average HA value of 0.81 among the five dams, and PD Jurala has slightly altered with an average HA value of 0.59. Out of the 33 parameters considered, 11 have alternated highly, with HA values ranging from 0.61 to 0.83. The impact of dams on the Krishna River has shown a typical hydrological alteration which might be the risk to the aquatic species. The output of this study will be helpful to the water managers with sufficient information to make a decision. [ABSTRACT FROM AUTHOR]

Anthropogenic impacts and climate change modify instream flow, altering ecosystem services and impacting on aquatic ecosystems. Alpine rivers and streams on the Qinghai‐Tibet Plateau (QTP) are especially vulnerable to disturbance owing to limited taxonomic complexity. The effects of flow have been studied using specific taxa, yet the flow‐biota relationships of assemblages are poorly understood. A multi‐metric habitat suitability model (MM‐HSM) was developed using integrated measures of entire macroinvertebrate assemblages to substitute for habitat suitability indices derived from individual taxa. The MM‐HSM was trained using macroinvertebrates data from three alpine rivers on the QTP, including the Yarlung Tsangpo, the Nujiang, and the Bai rivers, and then validated using data from a forth alpine river (the Lanmucuo). The model produced predictions using the training data set (R2 = 0.587) and the validation data set (R2 = 0.489). By coupling the MM‐HSM with hydrodynamic simulations, the relationship between weighted usable area and flow (0.11–1.99 m3 s−1) for macroinvertebrate assemblages was established, whereby a unimodal response pattern was observed for the Lanmucuo River. This contrast with monotonically positive or negative relationships observed for individual indicator taxa further supported our hypothesis that the response pattern of entire macroinvertebrate assemblages to flow would differ from responses of individual indicator taxa. The MM‐HSM provides a novel framework to quantify flow‐biota relationships, which is a useful approach for integrated river management. Plain Language Summary: Anthropogenic impacts and climate change modify the flow of rivers. Aquatic ecosystems in alpine rivers, such as those on the Qinghai‐Tibet Plateau (QTP), are especially vulnerable to flow variations. Effects of flow on the fauna have been studied mostly in individual species, whereas the response of entire communities to flow is poorly understood. In this study, we collect macroinvertebrates and measure environmental conditions in four alpine rivers on the QTP. We propose an index to describe the integrated status of macroinvertebrate communities by using multivariate statistical and regression analyses, and couple this index with the hydrodynamic simulation to model how entire macroinvertebrate communities respond to flow in a representative alpine river. Our results show that macroinvertebrates respond first positively then negatively to flow, yielding a suitable flow condition for entire communities from integrated and holistic perspectives. We compare the response of entire macroinvertebrate communities to flow with responses of individual species, and detect very different patterns. These results provide a new perspective and strategy for future river management in pursuit of integrated ecosystem conservation. Key Points: The multi‐metric habitat suitability model uses integrated measures of entire assemblages to substitute for indices of individual taxaThere is a unimodal relationship between macroinvertebrates and summer flow variations (0.11–1.99 m3 s−1) in the Lanmucuo RiverThe response pattern of entire macroinvertebrate assemblages to flow differs dramatically from responses of individual taxa [ABSTRACT FROM AUTHOR]

Developing environmental flow standards requires an empirical understanding of the relationship between species' ecology and instream flow. However, when congruent biological and hydrologic data are lacking, the accurate simulation of hydrologic metrics (HMs) corresponding to the locations of biological data is needed. Methods to predict HMs vary in formulation (i.e., statistical vs. process‐based hydrologic models), ability to simulate HMs across the full range of the hydrologic regime (i.e., magnitude, duration, frequency, rate of change and timing) and ability to transfer HMs from gaged to ungaged locations. Yet, despite the breadth of modelling approaches, less attention has been paid to the variability in HMs associated with each approach. In this study, we apply a distributed hydrologic model to the diverse watersheds of South Carolina to examine the predictability of HMs from simulated daily time series of streamflow across ecoregions, stream classifications and level of human alteration. In doing so, we contextualize the predictability of HMs, giving managers and researchers in South Carolina the flexibility of choosing HMs that are best suited for quantifying flow–ecology relationships based on the location, flow regime components of interest and uncertainty of HMs. We found that at least one HM within each of the five flow regime components (out of a selected subset of 41 non‐redundant HMs) was consistently and accurately predicted across the diverse streams of the study area. We discuss the patterns of predictability related to site characterizations and individual HMs and their implications for developing environmental flow standards. [ABSTRACT FROM AUTHOR]

Since the 1960s, rapid urbanization has caused serious deterioration in the quantity and quality of instream flows in South Korea. As demands for healthy instream ecology, landscape, and water-friendly environments have increased, the government has revised the relevant legal codes. In 2017, the environmental flow, defined as the minimum flow to conserve the health of aquatic ecosystems, has been endorsed in the Water Environment Conservation Act. However, owing to the lack of established criteria for the selection of target sites, the implementation of environmental flow is still in its early stage. This study suggests a simple flowchart to identify the preferential target sites for environmental flow estimation. First, deterioration in the health of aquatic ecosystems is identified by comparing the monitored Fish Assessment Index (FAI) with the standard suggested by the Ministry of Environment. Thereafter, the conditions of discharge and water quality of the instream flows are assessed. In the discharge analysis, linear regression is used for three flow metrics to analyze the interannual variability of discharge. Discharge deficiency is evaluated by comparing the drought flow (Q355) and the 10% mean annual flow. The load duration curve (LDC) is used in the water quality analysis. A case study is conducted for the Bokha-cheon Stream to test the flowchart, followed by a nationwide application. From the results, more than 70 sites have been identified as target sites for the estimation of the environmental flow in the five major river basins of Korea. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Effusion cooling in gas turbine combustors is complicated by swirling flows for anchoring flame, whereas miniature effusion cooling jets are highly directional. This work aims at understanding the directional effects of effusion cooling by studying the effectiveness of cooling film as a function of the offset flow angle ß between the main flow and effusion cooling jets. The directional effects of effusion cooling on the cooling film effectiveness are investigated at offset angles of 0, 30, 60, and 90 deg. The cooling film effectiveness is determined by invoking the heat/mass transfer analogy using pressure-sensitive paint that is sensitive to the oxygen partial pressure at the paint surface. Experimental results indicate that offset angles ß have a strong effect on the cooling film effectiveness. At lower coolant mass flow rates, an offset angle increases the uniformness of the cooling film because the flows from each individual hole coalesce together to form the protective film. At higher coolant mass flow rates, the cooling film effectiveness is less sensitive to the offset angles ß. This is believed to be caused by the coolant flow lifting off the surface and dissipating more easily in the mainstream flow. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Riffle 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. [ABSTRACT FROM AUTHOR]