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

Abstract

River 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.

Assessing the Performance of In-Stream Restoration Projects Using Radio Frequency Identification (RFID) Transponders

“…Models of widely ranging sophistication are available, with many examples of steady-state 2D and 3D models applied to as-built designs [15][16][17][18][19], and Large Eddy Simulation (LES) applied to the resolution of turbulence around isolated or idealized examples of in-stream structures [20,21]. Morphodynamic models are increasingly applied to predict channel evolution in the area surrounding implemented in-stream structures [22,23], and many laboratory studies have been carried out for this purpose [24][25][26][27][28][29].…”

Differences in river ecological functions due to rapid channel alteration processes in two California rivers using the functional flows model, part 2—model applications

“…A more sophisticated definition of the FFM that could be implemented in the future would analyse the spatial sequencing of shear stress to identify functional flows that assist pool-riffle sequence self-maintenance and other dynamics governed by channel non-uniformity (Lisle and Lewis, 1992;Macwilliams et al, 2006). The assumption of uniform flow is appropriate for a channel that does not change cross-section geometry in the downstream direction but may need to be checked depending on the conditions of a site (Brown and Pasternack, 2008;Pasternack et al, 2008). For instance, pool-riffle morphologies experience flow convergence, thus requiring the assessment of the relative importance of nonuniform terms to decide if they need to be included in the calculation of shear stress.…”

“…For instance, pool-riffle morphologies experience flow convergence, thus requiring the assessment of the relative importance of nonuniform terms to decide if they need to be included in the calculation of shear stress. One way of checking would be to compare the results of steady hydraulic calculations made with a cross-section analyser against those made with a 1D hydraulic flow model that accounts for backwater conditions (Brown and Pasternack, 2008).…”

Use of Ecohydraulic-Based Mesohabitat Classification and Fish Species Traits for Stream Restoration Design

“…Restoring stream habitat based on geomorphic classification of stream reaches can be limiting [29], but coupled with a hydraulic habitat model, species trait-based HSC can be incorporated into restoration design. In general, ecohydraulic models have been used in restoration projects, but their use is minor when considered with the number of projects constructed each year using the NCD method [19,91,102,[110][111][112].…”