Numerical analysis of effects of large wood structures on channel morphology and fish habitat suitability in a Southern US sandy creek

摘要

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. 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.