Spawning Habitat Rehabilitation Research Articles

Collaboration project of salmon spawning habitat rehabilitation between industry, research institute, government and citizen

Collaboration project of salmon spawning habitat rehabilitation between industry, research institute, government and citizen

Geomorphic controls on fine sediment reinfiltration into salmonid spawning gravels and the implications for spawning habitat rehabilitation

Anthropogenic activities often increase the flux of fine sediment to fluvial environments. In gravel-bed streams the extent to which augmented fines loading causes the degradation of vital interstitial habitats is determined by factors controlling fines infiltration into channel substratum. Previous research suggests that substrate pore constriction size, intensity of upwelling interstitial flow, and the quantity of fines transported across the bed surface (i.e., exposure dose) are three important factors controlling substrate fines content. Few field studies have investigated the interactive effects of these physical factors. We constructed 17 experimental redds in brook trout spawning microhabitats in a boreal forest stream in Quebec, Canada, to investigate the role of pore constriction size, hyporheic flow, and exposure dose on substrate fines content. To simulate the effect of spawning in coarsening the substrates, redds were partially cleaned of coarse sand and of all fine sediment (<0.5mm). Results show that coarse sands and fine gravel (0.5–4mm; filter class) acted as a filter of percolating fine sediment (<0.5mm). We found that this filtering effect (i.e., lower fines density at egg pocket depth) occurred at sites where the proportion of the filter class in the substratum above egg pocket depth exceeded a threshold value of 18%, as indicated by a statistically significant step-function response between fines gradient with depth and the filter class content in the uppermost layers of the bed. Results also indicated that fines content at depth was unrelated to fines exposure. Estimated upward seepage rates were well below the threshold velocity that would inhibit the percolation of medium-grained sand (i.e., 0.5mm) into the bed. These results suggest that within these gravel-bed spawning substrates the abundance of filter classes was the primary determinant of fines content at depth. This study highlights the importance of considering filter class content in the implementation of spawning habitat rehabilitation schemes and when assessing the susceptibility of incubation microhabitats to augmented fine sediment loading to streams.

Large wood aids spawning Chinook salmon (Oncorhynchus tshawytscha) in marginal habitat on a regulated river in California

AbstractTo determine whether large wood (LW, ≥1‐m length, ≥10‐cm diameter) plays a role in Chinook salmon (Oncorhynchus tshawytscha) redd (i.e. egg nest) placements in a regulated, Mediterranean‐climate, medium‐sized river (where channel width is less than the upper quartile of length of potential instream wood pieces), characteristics of 527 large wood pieces, locations of 650 redds, and mesohabitat delineations (riffle, run, glide, pool) were collected during a spawning season along a 7.7 km reach directly below Camanche Dam on the Mokelumne River, CA. LW was regularly distributed across the study reach an average 70 LW pieces km‐1. Some LW clustering was evident at islands and meander bends. Spawners built 85% of redds within one average channel width (31 m) of LW. Spawners utilized LW within a 10 m radius 36% of the time in the upper 3 km rehabilitated reach, and 44% of the time in the lower 4.7 km marginal habitat reach. A greater percentage of LW was utilized in riffles in the upper 3 km reach where 90% of redds were built, while a larger percentage of spawners used LW in riffles in the lower 4.7 km reach. LW‐redd interactions occurred at greater rates than by random chance alone in the lower 4.7 km reach, which implies that LW aids spawning in marginal habitats. River managers and salmonid spawning habitat rehabilitation (SHR) projects should take LW additions into consideration as an important component of river rehabilitation. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Linking geomorphic changes to salmonid habitat at a scale relevant to fish

AbstractThe influence of geomorphic change on ecohydraulics has traditionally been difficult to quantify. With recent improvements in surveying technology, high‐resolution, repeat and topographic surveys have become a common tool for estimating fluvial sediment budgets and documenting spatial patterns of net erosion and net deposition. Using a case study from a spawning habitat rehabilitation (SHR) project on California's Mokelumne River, some new DEM‐differencing analytical tools and ecohydraulic models were used to test whether hypotheses about pool‐riffle maintenance mechanisms used in designing SHR projects were producing self‐sustaining spawning habitat when subjected to competent flows. Following peak flows associated with the spring snow‐melt, a total of 999.6 m3 of erosion and 810.1 m3 of deposition were recorded throughout the study area, with a net loss of 196.2 m3. Using an ecohydraulic spawning habitat suitability model to segregate the sediment budget, over 53% of the area in which gravel was placed in a 2005 SHR retained the same habitat quality characteristics, and 22% improved. The response to the flood was generically characterized by shallow deposition associated with areas of divergent flow over riffles and scour associated with areas of convergent flow in pools. Areas where habitat remained stable generally experienced only low‐magnitude elevation changes, and accounted for only 19.5% of the total volumetric change. Areas where habitat quality degraded (primarily pool exit slopes) were dominated by larger magnitude erosion and made up 46% of the total volumetric change. By contrast, areas where habitat quality improved (primarily constructed riffle) accounted for 34.5% the total volumetric change, and were dominated by shallow, low magnitude deposition. The results support hypotheses about pool‐riffle maintenance mechanisms used to design the rehabilitation projects, while also highlighting some simple but powerful techniques for linking ecohydraulic and geomorphic field monitoring data at a salmon‐relevant spatial scale. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Comparison of methods for analysing salmon habitat rehabilitation designs for regulated rivers

AbstractRiver restoration practices aiming to sustain wild salmonid populations have received considerable attention in the Unites States and abroad, as cumulative anthropogenic impacts have caused fish population declines. An accurate representation of local depth and velocity in designs of spatially complex riffle‐pool units is paramount for evaluating such practices, because these two variables constitute key instream habitat requirements and they can be used to predict channel stability. In this study, three models for predicting channel hydraulics—1D analytical, 1D numerical and 2D numerical—were compared for two theoretical spawning habitat rehabilitation (SHR) designs at two discharges to constrain the utility of these models for use in river restoration design evaluation. Hydraulic predictions from each method were used in the same physical habitat quality and sediment transport regime equations to determine how deviations propagated through those highly nonlinear functions to influence site assessments. The results showed that riffle‐pool hydraulics, sediment transport regime and physical habitat quality were very poorly estimated using the 1D analytical method. The 1D and 2D numerical models did capture characteristic longitudinal profiles in cross‐sectionally averaged variables. The deviation of both 1D approaches from the spatially distributed 2D model was found to be greatest at the low discharge for an oblique riffle crest with converging cross‐stream flow vectors. As decision making for river rehabilitation is dependent on methods used to evaluate designs, this analysis provides managers with an awareness of the limitations used in developing designs and recommendations using the tested methods. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Construction constraints for geomorphic‐unit rehabilitation on regulated gravel‐bed rivers

AbstractThe emergent practice of applied river restoration uses best available equipment and contouring methods to construct detailed designs with some features at scales as small as 0.5‐m relief. As part of adaptive management, it is necessary to determine the practicability of design features and construction methods before widespread adoption. In this study, we compared design versus as‐built topography for five salmonid spawning habitat rehabilitation projects at riffle‐pool geomorphic units on the lower Mokelumne River, California, USA. These were built instream using rubber tire front loaders. Digital elevation models (DEMs) of each site were produced for pre‐project, design and as‐built conditions. DEM differencing was used to compare the as‐built surface against corresponding design surfaces at each site to identify deviations. Causes of each identified deviation were assessed based on subjective observations by a team during construction. Across the projects, 70% of as‐built topography was within ±0.15 m of design specifications. Of the 30% deviating from the design, 41% was overfilled and 59% underfilled. The 30% of rehabilitated channel area that deviated from designs did not affect predicted areas of high‐quality spawning habitat. On‐site factors that hindered accurate construction of designs included front loader fording depth, poor operator elevation estimation, operator spatial disorientation and wood obstructions. In addition, funding and project management uncertainties caused gravel supply deficits and gravel bulk density estimation errors. It is concluded that constructing broad (&gt;0.5‐m relief) features of process‐based salmonid spawning habitat rehabilitation projects by gravel augmentation is practicable. However, uncertainties attributed to human error and available methods inhibit detailed (&lt;0.5‐m relief) rehabilitation. Despite uncertainties, limitations and errors, following the recommendations reported in this study would improve the as‐built adherence to design specifications of future projects. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Engineered channel controls limiting spawning habitat rehabilitation success on regulated gravel-bed rivers

In efforts to rehabilitate regulated rivers for ecological benefits, the flow regime has been one of the primary focal points of management strategies. However, channel engineering can impact channel geometry such that hydraulic and geomorphic responses to flow reregulation do not yield the sought for benefits. To illustrate and assess the impacts of structural channel controls and flow reregulation on channel processes and fish habitat quality in multiple life stages, a highly detailed digital elevation model was collected and analyzed for a river reach right below a dam using a suite of hydrologic, hydraulic, geomorphic, and ecological methods. Results showed that, despite flow reregulation to produce a scaled-down natural hydrograph, anthropogenic boundary controls have severely altered geomorphic processes associated with geomorphic self-sustainability and instream habitat availability in the case study. Given the similarity of this stream to many others, we concluded that the potential utility of natural flow regime reinstatement in regulated gravel-bed rivers is conditional on concomitant channel rehabilitation.

Sediment budget for salmonid spawning habitat rehabilitation in a regulated river

Bed elevation, feature adjustments, and spawning use were monitored at three Chinook salmon ( Oncorhynchus tschawytscha) spawning habitat rehabilitation sites to measure project longevity in a regulated river. Sites enhanced with 649–1323 m 3 of gravel lost from 3–20% of remaining gravel volume annually during controlled flows of 8–70 m 3/s and 2.6–4.6% of placed material during a short-duration (19 days) release of 57 m 3/s. The oldest site lost ∼50% of enhancement volume over 4 years. Of the mechanisms monitored, gravel deflation was the greatest contributor to volumetric reductions, followed by hydraulic scour. Spawning, local scour around placed features, and oversteepened slopes contributed to volumetric changes. As sites matured, volumetric reductions decreased. Sites captured as much large woody debris as was lost. While complexity is an extremely important aspect of ecological function, artificial production of highly diverse and complex habitat features may lead to limited longevity without natural rejuvenation.

Application of a 2D hydrodynamic model to design of reach‐scale spawning gravel replenishment on the Mokelumne River, California

AbstractIn‐stream chinook salmon (Oncorhynchus tschawytscha) spawning habitat in California's Central Valley has been degraded by minimal gravel recruitment due to river impoundment and historic gravel extraction. In a recent project marking a new direction for spawning habitat rehabilitation, 2450 m3 of gravel and several boulders were used to craft bars and chutes. To improve the design of future projects, a test was carried out in which a commercial modelling package was used to design and evaluate alternative gravel configurations in relation to the actual pre‐ and post‐project configurations. Tested scenarios included alternate bars, central braid, a combination of alternate bars and a braid, and a flat riffle with uniformly spaced boulders. All runs were compared for their spawning habitat value and for susceptibility to erosion. The flat riffle scenario produced the most total, high, and medium quality habitat, but would yield little habitat under flows deviating from the design discharge. Bar and braid scenarios were highly gravel efficient, with nearly 1 m2 of habitat per 1 m3 of gravel added, and yielded large contiguous high quality habitat patches that were superior to the actual design. At near bankfull flow, negligible sediment entrainment was predicted for any scenario. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Spawning habitat rehabilitation ‐I. Conceptual approach and methods

Altered sediment and flow regimes in regulated rivers limit available spawning habitat for many fishes, especially salmonids. Mitigation efforts include spawning habitat rehabilitation and dam‐removal, but often neglect conceptual or predictive models of hydrogeomorphic and ecological processes. Complete restoration of processes necessary for maintaining spawning habitat is often unrealistic in regulated rivers. However, we present a framework for spawning habitat rehabilitation based on the premise that certain ecologic functions and geomorphic processes can be restored in a manner that facilitates testing of underlying scientific theories. SHIRA (Spawning Habitat Integrated Rehabilitation Approach) provides a science‐based, systematic framework for reach‐scale rehabilitation of salmonid spawning habitat in regulated rivers. This approach is driven by a mix of field data, conceptual models and numerical models to provide predictive and explanatory insight into the rehabilitation process. Conceptual models are advocated for developing multiple design scenarios and explicit hypotheses about hydrogeomorphic processes and ecologic functions provided by said designs. Hydrodynamic, habitat suitability and sediment entrainment models that test the potential validity of design hypotheses prior to construction are reviewed. It is presumed that the added insight would improve the outcome of rehabilitation projects and test underlying scientific theories against the rigors of real‐world uncertainties.

Spawning habitat rehabilitation ‐ II. Using hypothesis development and testing in design, Mokelumne river, California, U.S.A.

Rehabilitation of salmonid spawning habitat in regulated rivers through spawning bed enhancement is commonly used to mitigate altered sediment and flow regimes and associated declines in salmonid communities. Partial design‐phase predictive results are reported from the application of SHIRA (Spawning Habitat Integrated Rehabilitation Approach) on the lower Mokelumne River, California. The primary management goal of the project was to improve habitat for spawning and incubation life stages of fall‐run chinook salmon (Oncorhynchus tshawytscha). In the summer of 2001, we conducted a pre‐project appraisal followed by development and testing of 12 design scenarios. A subsample of eight design hypotheses, used in three of the design scenarios, is presented. Hydrodynamic, habitat suitability and sediment entrainment model results were used to test five of the eight design hypotheses. Two of the three hypotheses not tested were due to inadequate data on flow boundary conditions at high discharges. In September 2001, the project was constructed in a 152 m reach of the LMR from a final design based on all eight of the design hypotheses presented. Transparent hypothesis development and testing in design is emphasized as opposed to declaring success or failure from an ongoing long‐term monitoring campaign of the case study presented.

Salmon Spawning Habitat Rehabilitation on the Merced River, California: An Evaluation of Project Planning and Performance

From 1986 to 1995, over US$2.5 million has been spent or allocated for projects to modify channel conditions to improve spawning habitat for Chinook salmon Oncorhynchus tshawytscha in the Merced, Tuolumne, and Stanislaus rivers, tributaries to the San Joaquin River, California. We evaluated the planning, design and performance of the Riffle 1 B reconstruction on the Merced River. This is typical of the nine individual riffle reconstructions completed to date, involving excavation of the existing channel bed (here, to 0.6 m) and back-filling with smaller gravels believed to be more suitable for salmon spawning. We reviewed project documents, interviewed agency staff, and conducted field surveys to document channel conditions in 1994 for comparison with the project as constructed in 1990. The project planning and design did not consider the siteˈs geomorphic context nor processes of erosion and sediment transport under the current flow regime. As a consequence, spawning-sized gravel placed in the channel was scoured and transported through the site at a flow with a return period of 1.5 years. The need for spawning habitat enhancement in the Merced River is questionable, but if such projects are to be built, we recommend that the project planning and design consider the siteˈs geomorphic context and acknowledge the need for and provide funds for project maintenance, and that the performance of completed projects be systematically monitored and evaluated.