An integrated hydrologic model of a rainfall-dominated catchment was used to quantify existing and predict future streamflows relative to salmonid needs and evaluate the efficacy of flow enhancement strategies. Future climate scenarios indicate declines in summer rearing habitat of up to 22% and a shift towards earlier flow recession with some scenarios forecasting a complete loss of passable flow conditions for outmigrating smolts during drought. Significant mitigation of these adverse changes appears possible; simulating reservoir releases and reduced evapotranspiration (ET) through forest management produces increases in summer flows large enough to fully offset the predicted declines associated with even the direst climate projections. Adapting to reductions in flow during the salmonid outmigration season is more challenging, although reservoir releases or forest management could provide passable flow conditions that extend 9-35 days further into the outmigration season. In contrast, cessation of all surface water diversion did not meaningfully offset the predicted future reductions in streamflow. Streamflow enhancement effects were much greater in the portions of the watershed underlain by Coastal Belt units of the Franciscan Complex compared to areas underlain by Central Belt units, suggesting that flow enhancement work may be less impactful in basins with storage-limited hydrogeologic conditions. Successful adaptation to climate change in terms of streamflow may require increased emphasis on strategies such as reservoir releases and/or vegetation management that would reduce forest ET. Significant additional research linking specific forest treatments to long-term ET reductions and streamflow consequences is needed to optimize streamflow benefits of forest treatments.

Clogging of gravel-bed rivers is a major issue for fish and macro-invertebrate habitats as well as for groundwater-river exchanges. River clogging consists mainly of the deposition and infiltration of fine sediments within the bed matrix, which is a natural phenomenon but can be enhanced by human activities. Although there are several methods for estimating the degree of clogging, quantitative assessment of clogging remains challenging, not to mention the lack of comparison between these methods. We therefore implemented three quantitative methods for estimating clogging (bed material sampling, infiltration test, and interstitial water sampling), and assessed their effectiveness and suitability for application as a long-term monitoring solution. These methods were applied to a natural river bed characterised by high spatial heterogeneity of clogging. The results show good correlations between the different methods despite some scatter that can be linked to limitations of some methodologies in term of sampling itself or sampling depth. Indeed, sampling of the bed material using a McNeil sampler is limited to the first 15 cm below the surface, whereas the infiltration test or interstitial water pumping using a standpipe can be achieved for a depth deeper than 15 cm only. The infiltration test appears to be effective for relatively low clogging, while interstitial water sampling is more efficient for high clogging. The results also show that dissolved oxygen estimation alone may not be sufficient to accurately estimate physical clogging, particularly for cases of low clogging. However, it appears to be a good and simple complementary method to the interstitial water-sediment pumping method. The infiltration test and interstitial water-sediment sampling are simple, quick and easy to apply methods. The two methods are complementary, and suitable for a spatial clogging assessment, with the possibility of investigating a wide range of clogging degrees.

Rising water temperatures driven by climate change threaten culturally and economically important salmonid fisheries throughout the Upper Midwest. Unsuitable thermal regimes degrade the effectiveness of habitat restoration projects in the region, thus strategies for mitigating peak summer stream temperatures are of interest to state and non-profit fisheries managers. Using a process-based stream temperature model, this study explores the thermal impact of riparian tree planting and tree removal in a 179 km 2 watershed in the unglaciated Driftless Area of southwestern Wisconsin. By creating hypothetical riparian vegetation scenarios and systematically adding and removing woody vegetation from the banks we explore the influence of shade and channel geometry on July stream temperatures with an emphasis on salmonid thermal suitability. We used this model to analyze an 18.5 km study reach to identify management areas that have the most potential to buffer downstream water temperatures throughout the summer with added shade. We developed a downstream thermal change (DTC) metric to measure the magnitude and downstream distance of temperature change following stream alterations. The magnitude of stream cooling was mediated by channel width in our scenarios, with more pronounced thermal changes in narrower stream reaches (p<.05). Modeled tree planting scenarios decreased the maximum July maximum weekly average temperature (MWAT) and July maximum weekly maximum temperature (MWMT) within the study reach by 0.52 ℃ and 0.53 ℃ respectively. This study offers a workflow using free and open-source modeling tools to determine the thermal impact of restoration and prioritize future management efforts in cold water stream ecosystems.

Environmental high flows, or e-floods, released from dams to restore aquatic and riparian habitats are a key management strategy to mitigate the impacts of dam regulation. While there is extensive literature on the design and implementation of e-floods, the role of instream large wood—downed trees, trunks, branches, and root wads—in enhancing e-flood outcomes in regulated rivers has not been adequately explored. This paper presents insights from the Spöl River in the Swiss Alps, where years of observations highlight the significant impact of large wood on the success of e-floods. Large wood contributes to geomorphological dynamics, increases habitat complexity, and enhances ecosystem resilience, yet it has been largely overlooked in e-flood planning. The study argues that the inclusion of instream wood can define the difference between success and failure in e-floods by supporting the continuity of the wood regime, which, along with flow and sediment regimes, is crucial for ecological integrity, and emphasizes the importance of integrating wood management into e-flood design. The Spöl River serves as a case study, demonstrating how wood management during e-floods can restore or sustain essential functions, ultimately improving the ecological health of river systems. The insights gained can be applied to the management of other regulated mountain rivers.

Vegetation overgrowth in rivers worldwide has been a significant problem due to its potential to reduce flood-flowing capacity and cause biodiversity loss. This study tried to develop a model to predict vegetation recruitment during the initial stage of secondary succession, leading to vegetation overgrowth. This study chose a logistic regression model for predicting vegetation recruitment because of its simplicity and lower computational load than machine learning. The model was designed for the Kinu River in Japan, undergoing significant vegetation overgrowth. Data for the model development was obtained from UAV (unmanned aerial vehicle) aerial surveys and public databases. To ensure the model’s applicability beyond the training rivers, we trained the logistic regression model in its performance across different river flows and geomorphic characteristics, including the normal and flood times and the gravel-bed and sand-bed. The results indicated that the logistic regression model with three explanatory variables — the distance from the river stream, the relative height, and the vegetation existence history —was optimal for all rivers with the F-measures of 0.79 to 0.85. Additionally, using UAV imagery allowed for high spatial resolution in predicting vegetation recruitment. The best model’s prediction map of the vegetation recruitment demonstrated that it could accurately predict vegetation distributions along the main river channel for the gravel and sand beds.

The development of cascade reservoirs significantly alters the water temperature of a river basin. However, our understanding of the distribution of water temperature in river basins under high-intensity hydropower development conditions remains limited. In this study, we analyzed historical data and monitored the present water temperature of the Wujiang River to assess the effects of cascade reservoir construction on water temperature and fish populations. The results revealed that the construction of cascade reservoirs weakened the continuity of water temperature in the basin. Various hydrological and meteorological factors influenced the water temperature of downstream dams. Among these factors, the upstream water temperature significantly impacted the downstream channel. There was no obvious pattern in the time needed to reach the thresholds of critical temperature and accumulated temperature for typical fish species ( Coreius heterodon) in the study area. However, the water temperature downstream of the Pingzhai Reservoir did not reach the threshold by the end of the monitoring period, while the water temperature downstream of other reservoirs allowed for normal Coreius Heterodon development prior to spawning. Furthermore, the construction of cascade reservoirs resulted in a significant reduction in the amplitude of water temperature at the downstream Wulong hydrological station, intensifying the water temperature delay in the Wujiang River. The findings of this study provide valuable insights into the cumulative effects on water temperature in the context of high-intensity hydropower development.

This study seeks better understanding of linkages between channel morphology, streamflow, and aquatic habitat for the effective rehabilitation of imperiled species in rivers subjected to intensive water resource management. We focused on the variability of shallow, low-velocity (SLV) habitats over 50 years for a 56 km reach of the Rio Grande of central New Mexico (Middle Rio Grande). Hydraulic models used topographic data obtained through long-term systematic monitoring between 1962 and 2012 to derive relationships between discharge and SLV habitat availability. We developed a temporally integrated habitat metric (TIHM) to facilitate quantitative comparisons of SLV habitat availability over seasonal hydrologic periods (base flow, spring runoff, and summer low flow) for selected years representative of contemporary discharge variations. Results showed that SLV habitat availability, as captured by TIHM values, decreased on average by 83% over the study period (1962–2012), corresponding to completion of Cochiti Dam (1973), which profoundly altered flow and sediment regimes. Resulting channel incision and floodplain disconnection, caused shifts in discharge-habitat relationships whereby considerably higher discharges are required to produce equivalent increases in SLV habitat availability relative to pre-dam conditions. Ecological implications of losses to SLV habitat availability include recovery of the federally endangered Rio Grande Silvery Minnow Hybognathus amarus.

Intermittent streams exhibit regular patterns of drying and are widespread, but the patterns of drying between geographically close streams are not fully understood. We compared annual patterns of flow and drying among ten intermittent streams within a single drainage basin and determined how traditional hydrologic metrics described variation between streams. We installed stream intermittency sensors and evaluated stage height using low-cost methods. We evaluated landscape factors as potential drivers of flow patterns. Intermittent streams varied based on both high and low flow metrics, driven by a variety of landscape level factors, especially watershed size. Additionally, we compared the observed flow regimes within our system with an established soil and water assessment tool, finding that modeled streamflow patterns generally underrepresented observed drying within the system.

The Upper Mississippi River (UMR) represents one invasion front to bigheaded carps Hypopthalmichthys spp. in North America. Agencies often sample larvae to determine the conditions that bigheaded carp reproduction occurs, but the ability for conventional ichthyoplankton sampling to detect bigheaded carp reproduction compared to native fish is unknown. We used occupancy models to estimate larval bigheaded carp and native fish larvae detection probabilities and assessed how habitat type, Julian date, river discharge, and water temperature affect occupancy. We sampled larvae in pools 18-20 of the UMR every two weeks at the Iowa, Skunk, and Des Moines River confluences in backwater, side channel, and thalweg habitats. Detection probabilities increased with water volume filtered and was lower for larval bigheaded carp than freshwater drum, gizzard shad, and percids. Freshwater drum and bigheaded carp larvae had higher detection in thalweg and channel border habitats compared to backwaters. Occupancy of bigheaded carp peaked on June 19 th at 20°C, increased with discharge, and declined with coefficient of variation (CV) of water temperature and discharge. Gizzard shad and percids occupancy peaked on May 24 th and increased with CV of water temperature while occupancy of freshwater drum peaked on July 3 rd, decreased with CV of water temperature, and increased with water temperature. Our results indicate bigheaded carp are more difficult to detect than native larvae and identified conditions associated with larval occupancy that can be used to maximize detection and better understand when, where, and under what conditions larvae are present while accounting for imperfect detection.

Research in fluvial biogeomorphology largely aims to promote our understanding of the interactions between riparian vegetation and fluvial morphodynamics within riverine ecosystems. Starting at the end of last century, Angela M. Gurnell has made a major contribution to fluvial geomorphology by considering, in addition to water flow and sediment transport, explicitly riparian, and later also aquatic vegetation and thus significantly promoted the fluvial biogeomorphological approach from its beginnings until today. The objective of the present paper is to present a set of studies and results obtained over the last twenty years by the authors and many collaborators, including Angela M. Gurnell, on a panel of French rivers: Tech, Garonne, Isère and Allier Rivers. In particular, feedback mechanisms between fluvial morphodynamics and riparian vegetation dynamics were investigated directly in the field and also using high resolution remote sensing at the scale of individual plants, populations, communities and landscapes, as well as during semi-controlled ex situ experiments at the scale of individual plants. Collectively, the authors’ research conducted over the past 20 years contributed to elucidate some key aspects of the feedback dynamics between the lowest and highest levels of the riparian ecosystem organisation. This article presents and discusses those key aspects. The gradually obtained results contributed to better understand and quantify feedbacks between river morphodynamics and vegetation at nested spatiotemporal scales, from plant species traits to the riverine landscape. Furthermore, the biogeomorphological approach advocated for more than twenty years now, has clearly helped to contribute to the enlargement of the discipline of geomorphology to ecology as well as evolutionary ecology, and to the development of a more integrative vision to study earth surface processes.

Extreme hydroclimate events affect the thermal regimes of freshwater systems. In a four-year period spanning periods of flooding and severe drought in Southeastern South America (2019-2023), we monitored temperature variability in streams and floodplain lakes in an undammed tributary of the Lower Uruguay River, using Onset HOBO dataloggers and modeled daily streamflow (Q). We compare the performance of linear and nonlinear regression and generalized additive models (GAM) to evaluate how air temperature (T air) variability affects water temperature (T water) at daily, weekly and monthly time scales and under different Q percentile ranges. Mean daily temperatures ranged from 6.4ºC to 30.2ºC with daily maxima coinciding with record highs >40 ºC in T air and record low streamflow in summer months. Daily and weekly air-water relationships for rivers, streams and lakes were best fit by nonlinear sinusoidal models (Nash Sutcliffe Error - NSE ≥ 0.68). Extremely low-flow periods (<10% Q) showed a linear relationship to T air, while high-flow periods (>90%) showed a nonlinear sinusoidal air-water relationship. Moreover, high-flow events showed weaker T air-T water model perforamce than moderate to low flow periods. Preliminary comparisons between basin land-cover and T water suggest that forest cover favors lower T min. This study fills a geographical gap in thermal regime data in freshwater ecosystems in South America and suggests that extreme hydroclimate events have important implications for the thermal behavior of freshwater systems.

Integrating hydrogeomorphological principles into the restoration of degraded rivers can achieve sustainable results for a variety of objectives and human benefits that are consistent with the potential functioning of rivers as well as their uses. Despite recent management approaches inspired by these principles, several restoration projects largely involve controlling river processes and target specific one-dimensional objectives often associated with the habitat of a few high-valued fish species or with rivers steadiness and aesthetics. Although there is overall a lack of post-project monitoring, several projects appear to have failed or had mixed success. This research aims to answer the question: What are the real drivers behind river restoration projects? Four restoration projects in Quebec (Canada) were characterized through a qualitative research process of support and interviews with the organizations running them as well as with two representatives of ministries involved in river restoration and management. The results identify two major drivers for the formulation of restoration objectives: project funding and stakeholder expertise. We propose a new analytical framework including these drivers, which appear to act as both conditions and motivations guiding the objectives of the projects and their diversity. Following diverse sociocultural and legislative contexts shaping these drivers, they may facilitate or restrict the integration of hydrogeomorphological principles towards diversified objectives and benefits. This supports regulation that is better informed by scientific knowledge about hydrogeomorphological and sociocultural river dynamics, knowledge sharing between academic researchers and environmental organizations, and collaboration between stakeholders and communities living around rivers.

The anomalous variation in the diversion of flow and sediment at the major bifurcation nodes of the Pearl River network in recent years has been generally recognised and accepted, yet the underlying mechanisms have not been revealed. In this study, a large-scale two-dimensional flow-sediment numerical model of the Pearl River estuary was constructed using the TELEMAC-MASCARET modelling system. Additionally, synchronous field surveys from the dry season of 2016 and wet season of 2017 were used to validate the model. The complex branches system of the Pearl River network was generalised. The theoretical models for calculating the water diversion ratio of complex estuarine river networks were proposed. The water diversion ratio at each river network node is related to the Manning's roughness coefficient, the average cross-sectional water depth, the water surface slope, the length of the branches, and the average cross-sectional area from the river network nodes to the main estuary outlets. Specifically, the average cross-sectional water depth is the main driver of the formation of the water diversion ratios at the nodes in the Pearl River network. The sediment diversion ratios at the primary and secondary lateral branching nodes, are significantly higher than the water diversion ratios in the dry season, which explains the uneven distribution of flow and sediment. Sediment mining and reclamation are the main factors that have affected the variation in flow and sediment diversion ratios in the Pearl River network over recent decades.

Metals pollution and channel disturbance associated with historical mining, land use, and water development degraded aquatic and riparian habitat along the upper Arkansas River near Leadville, Colorado. Stream restoration was conducted for an 8 km reach to improve aquatic habitat and increase trout populations. Instream structures were prescribed to stabilize streambanks, create diverse stream morphology, and provide overhead cover, refuge, spawning, and overwinter habitat for trout. At least 90% of all structures were expected to be stable and functional three years after implementation. The objectives of this study were to investigate structure performance by (1) evaluating the integrity and function of instream structures and (2) evaluating the change in residual pool depths (RPD). Annual surveys utilized a rapid assessment procedure to qualitatively rank integrity, erosion, and deposition at each structure (n = 137). Rankings were investigated with ordinal regression to determine if performance varied by structure type and year. Longitudinal profile surveys were conducted annually and used to estimate RPD for 86 pools. The change in RPD was investigated with repeated measures ANOVA to determine if RPD varied between structure types and changed over time. Results suggest that some structures were more prone to failure, with higher rankings observed for boulder toe, log vanes, log toe, and boulder vanes. Pool depths increased during construction, decreased following the first runoff, and then remained relatively stable in subsequent years. Understanding the performance of instream structures from this case study will help inform the design, evaluation, and expectations for future stream restoration projects.

In this research, we explore whether a dendrogeomorphological assessment of tree scarring can accurately summarize past ice-jam flooding events occurring at a given reach of a river. A sample site was chosen with a history of ice-jam flooding located in close proximity to a river gauge station. Samples were collected along a 200-metre stretch of riverbank to capture the variation in elevations and possible different ice-jam flooding events. Disk samples were collected from trees with visual scarring evidence that indicated they had endured a past ice-jam event. Tree cores from an adjacent stand were collected to create a master chronology for each of the sampled species. Tree disks and cores were analyzed under a microscope using a Velmex stage system, then visually and statistically crossdated using the program COFECHA. Based on the last year of tree growth, years of individual injury events were established. The years of injury event dates were compared against the years of highest instantaneous maximum water elevations from gauged river data. The two data sets correlated, as years with highest recorded injury event dates were also the years of highest instantaneous water level elevations. The most common years of injury event dates were directly reflected in the top five years of highest river instantaneous water level elevations. In addition, the year of 2020 had the highest water elevations in the past 27 years, which was again reflected in the dendrogeomorphological data as the injury event year of 2020 was recorded on over 90% of the sampled tree disks. The correlation found between the gauged river data and the dendrogeomorphological data strongly suggests that past ice-jam flooding event dates can accurately be determined through the analysis of trees in riverbank stretches that have been impacted by ice-jams. The relationship of the gauged river data to the dendrogeomorphological data will therefore allow researchers to determine ice-jam site histories in remote areas where no gauged data exists. The site histories can provide information such as the years or heights that past ice-jam flooding occurred, which could then be used in ice-jam flooding hazard assessments.

Streamflow depletion is occurring globally, due to land use change, climate change, and increasing human water demand. Ecological effects of low flows are particularly significant for diadromous fish, which require connected stream networks to migrate between fresh and marine waters. In coastal California, USA, drying streams are known to limit rearing habitat for juvenile salmon, but effects on their seaward migration remain poorly understood. In this study, we evaluated the outmigration of endangered, juvenile coho salmon ( Oncorhynchus kisutch) during the late spring flow recession in four streams over 10 years. We monitored the outmigration of fish tagged with passive integrated transponders via detections at stationary antennas, and we measured stream water depths when movement was detected. We assessed depths at multiple riffle crest thalwegs (RCTs), the shallowest geomorphic feature that fish must navigate. Finally, we calculated population-level outmigration depth preferences by evaluating depths during fish movement, relative to depths available during the potential outmigration window. Juvenile fish moved over a wide range of depths (interquartile range 6.1–18.0 cm), which varied by year and stream. Fish ceased to move at shallow water depths, which limited late-season outmigration as stream drying occurred. Our findings suggest that management actions to increase streamflow during the spring would benefit salmon outmigration and could contribute to population recovery. Streamflow-RCT depth relationships, used to assess coho depth preferences during movement, is a relatively simple and effective method for assessing environmental flow needs, a priority for aquatic conservation in California and globally.

Leaf litter decomposition is a key ecosystem process that serves as a source of energy in stream ecosystems. However, land use change from forest to agricultural land has been reported to negatively affect stream ecosystem functions. Streams exhibit heterogeneity in terms of physical, chemical, biological characteristics and human-related influences. This may in turn affect stream ecosystem functions (e.g., leaf litter decomposition). However, information on the effects of land use and streambed topography on the functioning of many tropical stream ecosystems is still limited. This study assessed the influence of land use (i.e., forest vs agriculture) and streambed topography (i.e., riffles vs pools) on the decomposition rates of Syzygium guineense and Eucalyptus saligna leaf litter in the Kamweti River, Kenya. A total of 400 coarse-mesh litter bags were used to enclose 5 (± 0.05) g of each plant species leaf litter. The leaf litter was incubated in the selected study sites and litter bags were retrieved after 1, 3, 8, 14, 21, 28, 35, 42, 49 and 56 days of incubation. Physico-chemical parameters were also measured in all the sites. Decomposition rates were estimated using the negative exponential decay model. Linear Mixed-effect Models were used to evaluate the effect of land use, streambed topography and plant species on leaf litter decomposition rates. Physico-chemical water parameters differed significantly between the two land uses (all p < 0.05), except for pH and total nitrogen concentration ( p> 0.05). Forested sites ( Syzygium = 0.03 ± 0.004, Eucalyptus = 0.04 ± 0.004) had relatively higher mean leaf litter decomposition rates than agricultural sites ( Syzygium = 0.02 ± 0.004, Eucalyptus = 0.03 ± 0.006), although not significantly different. On the other hand, riffle habitats had significantly higher decomposition rates ( p<0.05) than pool habitats across the two land uses. Streambed topography had a significant effect on decomposition rates of leaf litter, as opposed to land use. Therefore, local scale factors are more important in the decomposition process than catchment scale factors in the Kamweti River. Stream conservation and management efforts should be directed to the local scale factors as opposed to only riparian and catchment factors.