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

Abstract

In-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 m 3 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 m 2 of habitat per 1 m 3 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.

Flow convergence routing hypothesis for pool‐riffle maintenance in alluvial rivers

“…[13] The two-dimensional finite element surface water modeling system (FESWMS) was used to analyze depth-averaged hydrodynamics following the approach of Pasternack et al [2004]. FESWMS solves the vertically integrated conservation of momentum and mass equations using a finite element method to acquire depth averaged 2D velocity vectors and water depths at each node in a finite element mesh.…”

“…Casulli and Zanolli, 2002;MacWilliams, 2004;Froehlich, 1989;Pasternack et al, 2004]. For this application, the models were validated using field data collected by Keller [1969] to the extent possible recognizing the technological limitations and differing purpose of the original work.…”

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

“…Tonina and Jorde (2013) [99] reviewed the application of 1D, 2D, and 3D hydraulic models for ecohydraulic studies; in addition to non-numerical models. Hydraulic 2D models based on the depth-averaged St. Venant equation are useful for restoration providing design information in both the longitudinal and lateral dimensions [100][101][102]. The River2D model also includes a habitat subroutine computing WUAs based on species preference relationships at each user-defined flow cell [103,104].…”

“…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].…”

“…Recent interpretation of 3D flow dynamics through the pool suggests that unique ecohydraulic relationships exist among the pool-front, -mid, and -rear areas, in addition to the submerged bar and riffle areas. With the use of a 2D or 3D hydraulic model, maintenance processes associated with velocity-and shear-reversal and flow acceleration-deceleration concepts can be tested during restoration design [19,91,102,159].…”