|Shields Jr, Fletcher|
Submitted to: Journal of Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2009
Publication Date: 10/1/2009
Citation: He, Z., Wu, W., Shields Jr, F.D. 2009. Numerical Analysis of Effects of Large Wood Structures on Channel Morphology and Fish Habitat Suitability in a Southern U.S. Sandy Creek. Journal of Ecohydrology. 2(3): 370-380. DOI: 10.1002/eco.60 [online]. Interpretive Summary: Stream habitat for fish is very complex, and quantitative methods are needed to measure habitat quality to allow stream managers to plan and design habitat restoration projects. To measure the effect of placing large wood structures in a severely eroded stream channel, a numerical model was used to compute the patterns of depth and velocity in a sharp bend in a stream in northern Mississippi with and without large wood structures placed along the eroding, outside bank. Results were summarized by using depths and velocities to compute two types of habitat quality indices. Indices based on velocity gradients were relatively insensitive to the large wood, although they did indicate habitat recovery. Indices based on water depth and velocity preferences of two of the native fish species were much more sensitive to large wood addition, consistent with field observations. These results are useful for scientists and stream managers who assess the effects of stream restoration on stream ecosystems.
Technical Abstract: A depth-averaged two-dimensional model was applied to simulate the effect of large wood structures (LWS) on flow, sediment transport, bed change, and fish habitat in a deeply-incised sharp bend in the Little Topashaw Creek, North Central Mississippi. The hydrodynamic simulation showed that the flow was retarded by the large wood matrices along the outer bank and accelerated in the main channel, thus causing deposition along the outer bank and erosion in the main channel, consistent with field observations. Effects on fish habitat were quantified using two approaches. Habitat evaluations using kinetic energy and circulation metrics indicated that LWS only slightly increased the diversity of physical conditions. Weighted usable areas (WUA) for two fish species, blacktail shiner (Cyprinella venusta) and largemouth bass (Micropterus salmoides), were computed using hydrodynamic simulations of three discharges before and after the LWS construction and habitat preference curves for depth and velocity. The results show that the values of WUA for both fish species were increased after LWS installation at all three discharges. The maximum increase of WUA for blacktail shiner was 22%, while the maximum increase for largemouth bass was 155%. Application of LWS improved the quantity and quality of fish habitats. Habitat evaluations based on computation of WUA were more sensitive to the influence of LWS than metrics based on velocity gradients.