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.
Fish stranding in rivers, due to rapid shoreline dewatering, often occurs during the down-ramping phases of hydropeaks enabling peak energy production. Multiple hydrological characteristics of hydropeaking and river morphology influence stranding, but little is known about their relative effects. The goal of our study is to identify how the combination of hydropeaking characteristics and the occurrence of morphological microstructure (e.g., puddles, scour pools) influence fish stranding. For this purpose, we used an extensive dataset of fish stranding observations collected over 3 years in spring at 48 stations along a 50 km-long river reach. We aimed (1) to characterize stranding events and their associated fish assemblages, and (2) to identify the spatial and temporal determinants of stranding. We found that the occurrence of morphological microstructures of the riverbed was the main factor explaining fish stranding. Scour pools are the most impacting microstructures, followed by scour puddles, humid zones, and alluvial puddles. Then, hydropeaking characteristics interact with morphology and modulate the intensity of stranding. Low flow ranges (low peak flow, low base flow) occurring after periods without hydropeaks induce particular “salmonid” and “super-stranding” events and other flow ranges induce regular stranding events. Salmonids are particularly subject to stranding at the beginning of the sampling period. Recommendations that emerged are (1) to act in priority on stations where stranding is most likely, by morphological operations or by installing attractive structures in the perennial area, and (2) to maintain attractive, perennial habitats in the low flow range of hydropeaks.
Large rivers are difficult to sample due to their size yet critical to monitor because humans heavily rely upon and alter them. Aquatic invertebrates are commonly used to assess the ecosystem quality of streams, but methods to sample these animals in large rivers are still being developed. We sampled aquatic invertebrates using two methods in the Snake River near Jackson, Wyoming. We used a Hess sampler to collect aquatic invertebrates in areas of the river that were <42 cm in depth and rock baskets in deeper areas that were near the bank. Hess samples collected more aquatic invertebrate taxa, and a higher proportion of Ephemeroptera, Plecoptera and burrowing taxa. Rock baskets collected a higher proportion of Trichoptera, filterers and clinging taxa. Bioassessment metrics differed between sampling methods; richness, diversity, evenness, Ephemeroptera, Plecoptera and Trichoptera (EPT) and Hilsenhoff’s biotic index produced higher values in Hess samples, and percent EPT was higher in rock baskets. Non-metric multidimensional scaling and analysis of similarity indicated that the samplers collected different assemblages (p < 0.001). The standard error of total invertebrate density was smaller when at least seven samples were collected and most species were collected when 6-7 replicate samples were processed within a reach. Understanding how sampling method alters the aquatic invertebrates collected will help managers develop monitoring protocols that are best suited to the river and collect the most unbiased invertebrate assemblages.
Streambank erosion impacts rivers and reservoirs due to bank erosion. However, little information of stream bank is available due to the need for advanced planning. Dendrogeomorphology offers a post-hoc method to calculate streambank erosion providing information about past erosion events and processes. Bank retreat can be calculated by dendrogeomorphology where the distance from a channel bank of an exposed live root shows anatomical changes that are dated from the root’s growth rings. We estimated bank erosion for three different sized southern U.S. watersheds ranging in area from 4 to 3781 km 2 using dendrogeomorphology compared to modeled erosion based on critical velocity required for sediment transport. Erosion values ranging from 3.8 to 13.5 cm/yr for the smaller drainages with no difference found between root and modeled erosion rates. The large sub-basin had erosion ranging from 33.6 to 196.4 cm/yr with high variance associated with two prior 2-year flow events with significant differences found between root and modeled values. We also found distance to bank strongly and positively correlated with root exposure in straight sections of the channel in contrast to roots collected in meander bends attributed to erosion processes (i.e., scour, mass wasting) occurring at these locations. When compared with other erosion studies across the southern U.S. prairie, our values were similar in magnitude but with low correlation to drainage area indicating site specificity of erosion mechanisms. We confirm dendrogeomorphology provides reasonable estimate of bank erosion across multiple spatial scales, important for watershed management in areas lacking intentional and persistent monitoring.
The upper Colorado River is a highly regulated system that provides habitat for federally listed species, disproportionate number of flora and fauna and is the water supply for the western United States. River regulation has led to wide scale channel narrowing. Over the last three decades dams have been operated with a more natural hydrograph for environmental reasons. We sought to use remote imagery from 1940-2022 to examine rates of channel narrowing in the pre-dam, post-dam, and environmental flows eras along three river reaches in Canyonlands National Park. We found an increase in the vegetated area along the Colorado River (above the confluence with the Green River) and the Green River since 1940. We documented a 6.12% and 4.00% narrowing in the post-dam period and a 19.51% and 6.49% narrowing in the environmental flows period on the Colorado and Green Rivers, respectively. The Cataract Canyon reach (Colorado River below the confluence) has been stable since 1966. All three river reaches showed the slowest period of narrowing in the last 16 years of environmental flows that coincided with a large peakflow in 2011. All three reaches showed a decrease in vegetated area after the 2011 flood, followed by an increase in vegetated area to similar levels to before the 2011 flood. Environmental flows that mimic the natural hydrograph may have slowed channel narrowing, but it is clear that periodic large peaks are also necessary. Managers must be careful that any environmental flows that take from the spring peak are carefully considered.
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.
This study was conducted to meet regulatory requirements under the Fisheries Act in Canada, specifically for a hydroelectric facility on the Yellowknife River in the Northwest Territories. The research focused on annual snorkel surveys of adfluvial fish and their spawning habitat below the facility. Initial observations of egg mortality, potentially due to overcrowding, prompted the investigation of natural and enhanced habitat for spawning Lake trout ( Salvelinus namaycush), lake whitefish ( Coregonus clupeaformis) and cisco ( Coregonus artedi) from 2016 to 2019. The design and composition of the installed habitat were based on fish utilization of the natural channel below the hydro facility and design principles from previous habitat rehabilitation projects for anadromous fishes. Pre- and post-enhancement data on egg density and survival were collected using 1 m 2 plots on both natural and artificially enhanced substrates. Three years of post-enhancement monitoring indicated higher egg densities and a greater proportion of live eggs in the artificially enhanced habitat compared to the natural habitat, with more pronounced trends observed for coregonids (lake whitefish and cisco) compared to lake trout. These findings suggest that habitat enhancement has the potential to enhance juvenile recruitment for adfluvial fish. A critical factor in the design was the substrate composition, providing adequate interstitial spaces for egg development and protection. This study represents the first documented attempt at habitat improvement in a regulated sub-Arctic river in Canada. The findings offer valuable guidance for stakeholders involved in new or existing development projects that require conservation actions to maintain fisheries productivity.
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.