Unregulated River Research Articles

Fate of juvenile salmonids stranded in off-channel pools: implications for nutrient transfers

Fish stranding is a complex phenomenon largely attributed to anthropogenic causes in regulated rivers. Although our knowledge of the frequency of stranding and fate of stranded fish in unregulated rivers is limited, this phenomenon may be widespread and important for the transfer of nutrients from aquatic to terrestrial ecosystems. Using a combination of observational data, an experimental manipulation, and a nitrogen subsidy model, we investigated the fate and implications of fish stranded in off-channel pools created by the last spring flood, in the Kadashan River watershed on Chichagof Island, Alaska, USA. Of fish stranded in pools (exclusively juvenile Dolly Varden Char [Salvelinus malma] and Coho Salmon [Oncorhynchus kisutch]), smaller individuals (age-0; 74 mm). Mortality rate was mainly influenced by cover availability, and larger fish tended to disappear at a higher rate than smaller ones. These observations, together with detection of predator activity, suggest that predation was the main cause of mortality for stranded fish. We estimate that fish stranding occurred during 66% of the years between 1980 and 2015, and that in a single stranding event approximately 1.62 kg of nitrogen is available to predators in the 0.24 km2 floodplain of the Kadashan watershed surveyed. Thus, fish stranding likely has implications for cross ecosystem connectivity via aquatic nutrient transfers to terrestrial food webs. With projected increases in extreme precipitation and flood events in Southeast Alaska the incidence of fish stranding in unregulated rivers will likely increase. Our results suggest by ensuring that cover (e.g. large wood and artificial structures) is available in off-channel habitats to benefit species or populations of conservation concern.

The transport of sediments by released anchor ice

The impact of sediment transport by anchor ice release on the annual sediment budgets of rivers is unknown. Sediment transport on regulated rivers could be significant since open water persists throughout the winter season and anchor ice forms and releases often. Studies that quantify the amount of sediment carried or rafted by released anchor ice pans are rare and have been performed on unregulated rivers with significantly different flow regimes, or have few collected samples. In this study, anchor ice samples were collected on three regulated rivers in Alberta: the North Saskatchewan, Peace and Kananaskis River. Previous studies on the amount of sediment contained in anchor ice are discussed and compared. Gravel and cobble sized particles were also sampled from anchor ice pans as they floated by to better understand the largest sediment anchor ice transports. The sampled gravels and cobbles contained in anchor ice showed that 24% of the total sampled mass came from only 1.2% of the particles sampled. The average sediment concentration contained in released, floating anchor ice was found to be 28.2g/L, with a standard deviation of 33.2g/L, and a median of 18.4g/L. This information will allow for more accurate estimations of how transport of sediment by anchor ice releases affects the annual sediment budget on regulated rivers.

Movement and Habitat Use of Alligator Gars in the Escambia River, Florida

AbstractIn Florida, the population status of the Alligator Gar Atractosteus spatula is unknown, and harvest of this species was prohibited in 2006. Although abundance estimates are needed, first information about its habitat use and life history is required. We examined movement, habitat use, and home range of Alligator Gars in the Escambia River, an unregulated coastal river in Florida. Twenty‐two fish (TL range = 92–193 cm) were captured by using large‐mesh gill nets and were tagged with external transmitters. Detachment of tags resulted in 16 fish being tracked for the study (tag retention time = 2–19 months). Seasonal movements of fish were monitored by active daytime tracking and via fixed‐station receivers to determine home and core ranges. Results suggested that Alligator Gar movement was seasonal and related to water temperature. Mean linear home ranges and core ranges were each approximately five times smaller during the cold season (water temperature ≤ 15°C) than during the warm season (>15°C). Diel movement and habitat information was collected (N = 8 Alligator Gars per season) from arrays of fixed‐station receivers that recorded data continuously for 24 h during deployment. Individuals moved little and at a lower travel rate during 24‐h periods in the cold season, whereas they became highly mobile during the warm season, moving at a higher travel rate. Alligator Gars spent proportionally more time in main‐channel habitat (62.5%) during the warm season and in off‐channel habitat (84.2%) during the cold season, but no difference in diel use of these habitats was evident between seasons. An understanding of movement patterns and habitat use could lead to increased catch, thereby improving the accuracy of abundance estimates and the reliability of population assessments. Comprehensive knowledge of these behaviors should help to guide conservation and management efforts in regulated and unregulated rivers throughout the Alligator Gar's range.Received January 24, 2017; accepted June 9, 2017Published online August 10, 2017

Range estimates and habitat use of invasive Silver Carp (Hypophthalmichthys molitrix): evidence of sedentary and mobile individuals

Unregulated rivers provide unobstructed corridors for the dispersal of both native and invasive species. We sought to evaluate range size and habitat use of an invasive species (Silver Carp, Hypophthalmichthys molitrix) in an unimpounded river reach (Wabash River, IN), to provide insights into the dispersal of invasive species and their potential overlap with native species. We hypothesized that range size would increase with fish length, be similar among sexes, and vary annually while habitats used would be deeper, warmer, lower velocity, and of finer substrate. Silver Carp habitat use supported our hypotheses but range size did not vary with sex or length. 75% home range varied annually, suggesting that core areas occupied by individuals may change relative to climate-based factors (e.g., water levels), whereas broader estimates of range size remained constant across years. Ranges were often centered on landscape features such as tributaries and backwaters. Results of this study indicate habitat and landscape features as potential areas where Silver Carp impacts on native ecosystems may be the greatest. Observed distribution of range sizes indicates the presence of sedentary and mobile individuals within the population. Mobile individuals may be of particular importance as they drive the spread of the invasive species into new habitats.

Water Temperature Ensemble Forecasts: Implementation Using the CEQUEAU Model on Two Contrasted River Systems

In some hydrological systems, mitigation strategies are applied based on short-range water temperature forecasts to reduce stress caused to aquatic organisms. While various uncertainty sources are known to affect thermal modeling, their impact on water temperature forecasts remain poorly understood. The objective of this paper is to characterize uncertainty induced to water temperature forecasts by meteorological inputs in two hydrological contexts. Daily ensemble water temperature forecasts were produced using the CEQUEAU model for the Nechako (regulated) and Southwest Miramichi (natural) Rivers for 1–5-day horizons. The results demonstrate that a larger uncertainty is propagated to the thermal forecast in the unregulated river (0.92–3.14 °C) than on the regulated river (0.73–2.29 °C). Better performances were observed on the Nechako with a mean continuous ranked probability score (MCRPS) <0.85 °C for all horizons compared to the Southwest Miramichi (MCRPS ≈ 1 °C). While informing the end-user on future thermal conditions, the ensemble forecasts provide an assessment of the associated uncertainty and offer an additional tool to river managers for decision-making.

Morphological differentiation in northern pike (Esoxlucius): the influence of environmental conditions and sex on body shape

Morphological differentiation may allow individuals to cope with prevailing environmental conditions. Morphological differentiation in fish characterized by sagittiform shape and ambush predator behaviour, such as northern pike (Esox lucius L., 1758), has rarely been addressed. Morphological differentiation was assessed in two rivers exhibiting contrasting flow regimes: a hydropeaking river characterized by large and frequent fluctuations in flow rates and an unregulated river. An increase in northern pike movement rate was observed in the hydropeaking river. Therefore, morphological features enhancing sustained and burst swimming, as well as manoeuvrability, were expected. Our objectives are to (i) compare morphology between the two rivers and (ii) assess morphological differentiation between sexes. Using geometric morphometrics, shape significantly diverged between rivers irrespective of sex and between sexes in the hydropeaking river. Individuals from the hydropeaking river had more elongated heads, deeper bodies and caudal peduncles, and longer dorsal fin insertions than individuals from the unregulated river. Caudal fin differences between rivers were not consistent between sexes. Morphological differentiation suggested a trade-off among adaptations for sustained and burst swimming, as well as manoeuvrability, to cope with variable flows in a hydropeaking river. Morphological differentiation may allow the exploitation of spatially and temporally variable environmental conditions, including those stemming from river flow regulation.

Growth characteristics of Eucalyptus camaldulensis trees differ between adjacent regulated and unregulated rivers in semi-arid temperate woodlands

River red gum (Eucalyptus camaldulensis) is the most widely-distributed eucalypt, an important timber resource, and critical to the sustainable function of many Australian waterways. Agricultural development, including decades of river regulation, has resulted in extensive degradation of E. camaldulensis woodlands, and restoration is now required to maintain ecological function in many floodplain areas. To aid restoration planning, we quantified the structural characteristics of E. camaldulensis trees in an intensively farmed region of eastern Australia. We studied tree populations on two rivers with different hydrological regimes: (1) Bogan River - ephemeral and surrounded by dryland agriculture, and (2) Macquarie River - permanent and the focus of irrigated agriculture. The two populations showed clear differences in allometric relationships. Trees on the ephemeral river were shorter with relatively wider canopies than trees with similar stem diameter on the permanent river. Trees on the ephemeral river progressed through stages of senescence at smaller stem sizes than those on the permanent river. Tree growth was episodic and strongly related to tree senescence, but the amount of growth in stem diameter was less on the ephemeral river. Tree senescence and stem diameter had the strongest effects on the probability of trees bearing hollows, with a lesser interactive effect of river hydrology. Variation among individual trees, sites and sub-catchments was large and not fully explained by the site characteristics measured. Our data enable predictions of future vegetation growth and fauna habitat development in semi-arid riparian woodlands that are not managed for silvicultural production. Our findings indicate that differences in the hydrological regimes of inland rivers manifest as differences in structural attributes of E. camaldulensis, even among individuals occupying the same catchment management area. Such differences should be reflected in future management strategies to sustain the function and biodiversity of riparian forests and woodlands.

Development and application of a large scale river system model for National Water Accounting in Australia

Existing global and continental scale river models, mainly designed for integrating with global climate models, are of very coarse spatial resolutions and lack many important hydrological processes, such as overbank flow, irrigation diversion, groundwater seepage/recharge, which operate at a much finer resolution. Thus, these models are not suitable for producing water accounts, which have become increasingly important for water resources planning and management at regional and national scales. A continental scale river system model called Australian Water Resource Assessment River System model (AWRA-R) has been developed and implemented for national water accounting in Australia using a node-link architecture. The model includes major hydrological processes, anthropogenic water utilisation and storage routing that influence the streamflow in both regulated and unregulated river systems. Two key components of the model are an irrigation model to compute water diversion for irrigation use and associated fluxes and stores and a storage-based floodplain inundation model to compute overbank flow from river to floodplain and associated floodplain fluxes and stores. The results in the Murray-Darling Basin shows highly satisfactory performance of the model with median daily Nash-Sutcliffe Efficiency (NSE) of 0.64 and median annual bias of less than 1% for the period of calibration (1970–1991) and median daily NSE of 0.69 and median annual bias of 12% for validation period (1992–2014). The results have demonstrated that the performance of the model is less satisfactory when the key processes such as overbank flow, groundwater seepage and irrigation diversion are switched off. The AWRA-R model, which has been operationalised by the Australian Bureau of Meteorology for continental scale water accounting, has contributed to improvements in the national water account by substantially reducing accounted different volume (gain/loss).

Groynes: a factor modifying the occurrence of dragonfly larvae (Odonata) on a large lowland river

The regulation of rivers and their valleys has had a strong, negative influence on the maintenance of their original biota. Nevertheless, some hydro-engineering works conducted along already regulated rivers may be beneficial, creating habitats for endangered species and assemblages. Such works include the construction of groynes. We analysed this effect on the occurrence of dragonfly larvae along middle and lower stretches of the Oder, where groynes were built over a distance of 306km, creating an area of uniform habitat. We demonstrated that the presence of groynes increased not only the abundance of dragonfly larvae, but also the species richness and diversity of these insects. Habitats were recreated for assemblages typical of a river with highly diverse habitat conditions, from typically riverine assemblages to those occurring in oxbow lakes, also endangered by regulations. The fauna along the stretches with groynes was richer and more valuable than that along the stretches without groynes, achieving values approaching those obtained from modelled unregulated rivers. This can be put down to greater habitat heterogeneity and groyne-reduced levels of waves produced by ships. The presence of groynes provides the key to the restoration or stabilisation of the populations of certain species and to renaturalisation processes.

Rivers of Risk and Redemption in Gregory of Tours’ Writings

Rivers of Risk and Redemption in Gregory of Tours’ Writings

Effects of flow regime on benthic algae and macroinvertebrates - A comparison between regulated and unregulated rivers.

Natural fluctuations in flow are important for maintaining the ecological integrity of riverine ecosystems. However, the flow regime of many rivers has been modified. We assessed the impact of water chemistry, habitat and streamflow characteristics on macroinvertebrates and benthic algae, comparing 20 regulated with 20 unregulated sites. Flow regime, calculated from daily averaged discharge over the five years preceding sampling, was generally more stable at regulated sites, with higher relative discharges in winter, lower relative discharges in spring and smaller differences between upper and lower percentiles. However, no consistent differences in benthic algal or macroinvertebrate structural and functional traits occurred between regulated and unregulated sites. When regulated and unregulated sites were pooled, overall flow regime, calculated as principal components of discharge characteristics over the five years preceding sampling, affected macroinvertebrate species assemblages, but not indices used for ecosystem status assessment or functional feeding groups. This indicates that, while species identity shifted with changing flow regime, the exchanged taxa had similar feeding habits. In contrast to macroinvertebrates, overall flow regime did not affect benthic algae. Our results indicate that overall flow regime affected the species pool of macroinvertebrates from which recolonization after extreme events may occur, but not of benthic algae. When individual components of flow regime were analyzed separately, high June (i.e. three months before sampling) flow maxima were associated with low benthic algal taxon richness, presumably due to scouring. Macroinvertebrate taxon richness decreased with lower relative minimum discharges, presumably due to temporary drying of parts of the riverbed. However, recolonization after such extreme events presumably is fast. Generally, macroinvertebrate and benthic algal assemblages were more closely related to water physico-chemical than to hydrological variables. Our results suggest that macroinvertebrate and benthic algal indices commonly used for ecological status assessment are applicable also in regulated rivers.

Mercury levels in largemouth bass (Micropterus salmoides) from regulated and unregulated rivers

Within areas of comparable atmospheric mercury deposition rates methylmercury burden in largemouth bass populations vary significantly between regulated and unregulated rivers. To investigate if trophic dynamics strongly influenced pollutant body load, we sampled largemouth bass from two adjacent rivers, one regulated and one unregulated, and applied a suite of biochemical and stable isotope assays to compare their trophic dynamics. Total mercury burden in the bass from the unregulated Sipsey River (Elrod, AL, USA) and the regulated Black Warrior River (Demopolis, AL, USA) averaged 0.87 mg kg−1 and 0.19 mg kg−1 wet weight, respectively. For both populations, age, weight, and length were positively correlated with muscle mercury concentration. Compound specific stable isotope analysis of amino acids showed the trophic position of both populations was just under four. Quantitative and isotopic analysis of neutral lipid fatty acid of Sipsey River bass indicated a greater reliance upon the detrital component of the food web compared to Demopolis Reservoir bass which fed within the autochthonous, pelagic component of the food web. Since the close proximity of the rivers makes differences in atmospheric deposition unlikely and both populations had similar trophic position, our findings indicate that food web dynamics should be included among the factors that can strongly influence mercury concentration in fish.

A regional analysis of the impact of dams on water temperature in medium-size rivers in eastern Canada

Various studies have helped gain a better understanding of the thermal impacts of dams on a site-specific basis, but very few studies have compared the thermal impacts of varying types of dams within the same region. In this study, we conducted a regional-scale assessment of the impacts of dams on the thermal regime of 13 medium-size rivers in eastern Canada. The objectives of this study were to identify features of the thermal regime of rivers that are predominantly impacted by dams and to compare the impacts associated with different types of regulation (run-of-river, storage, peaking). The thermal regime of regulated and unregulated rivers was characterized using 15 metrics that described the magnitude, frequency, duration, timing, and rate of change of water temperature. Results indicate that storage and peaking dams impounding at least 10% of the median annual runoff generally (i) reduced the magnitude of water temperature variation at seasonal, daily, and subdaily timescales and (ii) increased the monthly mean water temperature in September. This regional assessment offers important insight regarding a generalized pattern of thermal alteration by dams, and this information could be used to guide biological monitoring efforts in regulated rivers.

Innovative Analysis of Runoff Temporal Behavior through Bayesian Networks

Hydrological series are largely characterized by a strong random component in their behavior. More noticeable changes in the behavior patterns of rainfall/runoff temporal series are recently being observed. These modifications are not a trivial issue, especially in regards to peculiarities, non-linearities, diffused influences or higher time orders of dependence. This study mainly aimed to analyze the temporal dependence of an annual runoff series dynamically. This approach comprises a coupling between classic techniques (Autoregressive Moving Average Model, ARMA) and novel ones, based on Artificial Intelligent for hydrological research (Bayesian Networks, BNs). An ARMA model was built to provide reliable data to populate BNs. Then, causal reasoning, through Bayes’s theorem, allows the identification of the logic structure of temporal dependences within time series. Furthermore, the resultant conditional probability permits the quantification of the relative percentage of annual runoff change, and provides the right time order of dependence. This research introduces an original methodology able to build a logic structure for a stochastic analysis of temporal behavior. This approach also aimed to provide a powerful and graphic modeling method for improving the understanding of the dynamic runoff series temporal behavior. This was successfully demonstrated in two unregulated river basin stretches, belonging to the Duero river basin which is the largest basin in Spain.

Modelling habitat distributions for multiple species using phylogenetics

In this paper, we describe an empirical approach to model community structure using phylogenetic signals. That approach combines information about the species (i.e. traits and phylogeny) with information about the habitat (i.e. environmental conditions and spatial distribution of sampling sites) and their interactions to predict the species responses (e.g. the local densities). As an application, we use the approach to model fish densities in rivers. In the model, the different species and size classes were described using a functional trait, body length, and phylogenetic eigenvectors maps whereas the sites were described using water velocity, depth, substrate composition, macrophyte cover, degree‐days, total phosphorus, and spatial eigenvector maps. The model (estimated using a regularised Poisson‐family generalised linear modelling approach) fitted the data well (likelihood‐based R2adj = 0.512) and showed fair predictive power (likelihood‐based cross‐validation R2 = 0.283) to predict the density of fish pertaining to 48 species totalling 143 combinations of species and size classes in 15 unregulated Canadian rivers. Using the model as a baseline to estimate the effect of flow regulation on community composition, we found that, with few exceptions, the densities of most fish species were lower in regulated than in unregulated rivers. Phylogenetics have been proposed to study community structure, but this is, to our knowledge, the first time phylogenetic information is used explicitly for numerical habitat modelling. We expect that models of that type will be in increasing demand now that development projects are routinely assessed through impact studies.

Reliability of lumped hydrological modeling in a semi-arid mountainous catchment facing water-use changes

Abstract. This paper explores the reliability of a hydrological modeling framework in a mesoscale (1515 km2) catchment of the dry Andes (30° S) where irrigation water use and snow sublimation represent a significant part of the annual water balance. To this end, a 20-year simulation period encompassing a wide range of climate and water-use conditions was selected to evaluate three types of integrated models referred to as A, B and C. These models share the same runoff generation and routing module but differ in their approach to snowmelt modeling and irrigation water use. Model A relies on a simple degree-day approach to estimate snowmelt rates and assumes that irrigation impacts can be neglected at the catchment scale. Model B ignores irrigation impacts just as Model A but uses an enhanced degree-day approach to account for the effects of net radiation and sublimation on melt rates. Model C relies on the same snowmelt routine as Model B but incorporates irrigation impacts on natural streamflow using a conceptual irrigation module. Overall, the reliability of probabilistic streamflow predictions was greatly improved with Model C, resulting in narrow uncertainty bands and reduced structural errors, notably during dry years. This model-based analysis also stressed the importance of considering sublimation in empirical snowmelt models used in the subtropics, and provided evidence that water abstractions from the unregulated river are impacting on the hydrological response of the system. This work also highlighted areas requiring additional research, including the need for a better conceptualization of runoff generation processes in the dry Andes.

Differences in movements of northern pike inhabiting rivers with contrasting flow regimes

AbstractLittle is known about the effect of short‐term flow changes on the movement of northern pike (Esox lucius L.). We conducted a comparative study in two rivers with different flow regimes (i.e. one regulated and one unregulated) to evaluate the extent to which adult northern pike movement is influenced by short‐term river flow conditions. Data on northern pike hourly movement were collected in northeastern Ontario on 40 individuals in the Mississagi River, a river subjected to extreme daily flow variations associated with hydro‐electric operations (i.e. hydropeaking), and the Aubinadong River, an unregulated river. Using manual tracking by radio‐telemetry, we found that northern pike moved at a higher rate in the river subjected to short‐term changes in river flow than in the unregulated river. Results also show that the relationship between movement of northern pike and flow can vary among rivers. In the Mississagi River, flow had a significant positive effect on northern pike activity, while the effect of flow in the Aubinadong River depended on water temperature. Moreover, fish in the Mississagi River utilized a restricted river section and travelled more laterally in comparison to fish inhabiting the Aubinadong River, where longer upstream‐downstream movements were more common. The present study contributes to our understanding of the effects of short‐term changes in flow on fish movement. This constitutes the first step towards assessing the effect of flow on fish habitat use, and eventually developing flow management strategies to mitigate impacts on fish. Copyright © 2016 John Wiley & Sons, Ltd.

Regional flow duration curves: Geostatistical techniques versus multivariate regression

A period-of-record flow duration curve (FDC) represents the relationship between the magnitude and frequency of daily streamflows. Prediction of FDCs is of great importance for locations characterized by sparse or missing streamflow observations. We present a detailed comparison of two methods which are capable of predicting an FDC at ungauged basins: (1) an adaptation of the geostatistical method, Top-kriging, employing a linear weighted average of dimensionless empirical FDCs, standardised with a reference streamflow value; and (2) regional multiple linear regression of streamflow quantiles, perhaps the most common method for the prediction of FDCs at ungauged sites. In particular, Top-kriging relies on a metric for expressing the similarity between catchments computed as the negative deviation of the FDC from a reference streamflow value, which we termed total negative deviation (TND). Comparisons of these two methods are made in 182 largely unregulated river catchments in the southeastern U.S. using a three-fold cross-validation algorithm. Our results reveal that the two methods perform similarly throughout flow-regimes, with average Nash-Sutcliffe Efficiencies 0.566 and 0.662, (0.883 and 0.829 on log-transformed quantiles) for the geostatistical and the linear regression models, respectively. The differences between the reproduction of FDC's occurred mostly for low flows with exceedance probability (i.e. duration) above 0.98.

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

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

Management of the Spring Snowmelt Recession in Regulated Systems

AbstractIn an effort to restore predictable ecologically relevant spring snowmelt recession flow patterns in rivers regulated by dams, this study defined a methodology by which spring flow regimes can be modeled in regulated systems from the quantifiable characteristics of spring snowmelt recessions in unregulated rivers. An analysis of eight unregulated rivers across the Sierra Nevada mountain range in California found that unregulated systems behaved similarly with respect to seasonal spring patterns and recession limb curvature, and thus prescribed flows could be designed in a manner that mimics those predictable characteristics. Using the methodology to quantify spring recession flows in terms of a daily percent decrease in flow, a series of flow recession scenarios were created for application in an existing hydrodynamic model for the regulated Rubicon River. The modeling results showed that flow recessions with slow ramping rates similar to those observed in unregulated rivers (less than 10% per day) were likely to be protective of native aquatic species, such as the Foothill yellow‐legged frog, while flows that receded at greater rates would likely result in desiccation of egg masses and potential stranding of tadpoles and fry. Furthermore, recession rates of less than 10% per day provided the most spatially diverse hydraulic habitat in the modeled domain for an appropriate duration in spring to support all native species guilds and maximize aquatic biodiversity.