Modeling changes in salmon spawning and rearing habitat associated with river channel restoration1

Abstract

The River2D two‐dimensional hydraulic and habitat model was used to simulate fall‐run chinook salmon (Oncorhynchus tschawytscha) spawning and fry and juvenile rearing habitat before and after restoration of stream channel sites for a range of streamflows on the Merced River and Clear Creek, California. For the Merced River, hydraulic and structural data were collected for four sites before and after restoration, representing all habitat types within the restoration reach. Habitat simulated for these sites was extrapolated to the entire restoration reach based on habitat mapping. For Clear Creek, hydraulic and structural data were collected for four sites before restoration and pre‐restoration habitat was simulated. The topographic plan for the restoration was used to simulate habitat after restoration. While the restoration generally increased spawning habitat, it was less successful for rearing habitat. The results of this modeling show how they can be used in a cost‐effective adaptive management framework to evaluate restoration project design prior to construction.