|Shields Jr, Fletcher|
Submitted to: National Sedimentaton Laboratory (NSL)- 50 Years of Soil & Water Research in a Changing Agricultural Environment
Publication Type: Proceedings
Publication Acceptance Date: 8/2/2008
Publication Date: 4/5/2011
Citation: Wu, W., He, Z., Shields Jr, F.D. 2011. Numerical analysis of effects of large wood structures on channel morphology and fish habitat suitability in Little Topashaw Creek. In: Proceedings of the conference "Fifty Years of Soil & Water Research in a Changing Agricultural Environment". National Sedimentation Laboratory, September 2-5, 2008, Oxford, Mississippi. CD-ROM. Interpretive Summary: Structures made from felled trees and large logs have been used for controlling stream channel erosion because they are relatively cheap and mimic natural habitat features. However, their ecological effects have not been quantified. 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 habitat quality indices for two native fish species with and without large wood structures present. The large wood improved the quantity and quality of fish habitats. These results are useful for scientists and stream managers who must quantify benefits of stream restoration on stream ecosystems.
Technical Abstract: A depth-averaged two dimensional (2D) model has been applied to simulate the effect of large wood structures (LWS) on flow, sediment transport, bed change, and fish habitat suitability in a deeply-incised sharp bend in the Little Topashaw Creek, North Central Mississippi. The hydrodynamic simulation shows 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 in agreement with field observations. A habitat evaluation using kinetic energy, vorticity, and circulation metrics indicated that LWS increased the diversity of flow pattern within stream habitats. The weighted usable area and overall habitat suitability index for two fish species, Blacktail Shiner (Cyprinella venusta) and Largemouth Bass (Micropterus salmoides), before and after LWS construction at various flow discharges were analyzed using a habitat suitability index model. LWS improved the quantity and quality of fish habitats.