Modeling Trout Habitat Enhancement with Boulder Clusters in Caney Fork River, Tennessee

A calibrated 2D hydrodynamic model of a popular recreational fishing reach in the tailwater of the Caney River was employed to evaluate the benefits of trout habitat enhancement with a boulder cluster field. Hydrodynamic modeling results were coupled with habitat suitability index (HSI) Models to quantify relative enhancement at a flow of 174 m³/s. Scenarios with alternative boulder cluster densities were simulated to obtain an optimum design density for juvenile Rainbow Trout based on the computed weighted usable area (WUA) from the coupled model output. The model predicted an optimal spanwise spacing B=1.50D₀–1.67D₀ and streamwise spacing L=2.00D₀–2.33D₀; where D₀ represents the least dimension of the base area of each cluster. The simulated boulder cluster field was located along the gravel bar approximately 80 m from the right bank, and occupied a 4800 m² area with 240 m streamwise length and a 20 m spanwise length. Each individual boulder cluster was composed of two layers of boulders, each of approximately 1 m in diameter. The study demonstrates a rationale methodology for designing a boulder cluster field in a tailwater that is subject to the frequent occurrence of high flows. However, the assessment of WUA is found to be sensitive to both the weighting coefficients and the suitability index (SI) curves; which in turn depend on the flow discharge, the trout species and the life stage being considered.