Stream Erosion Potential and Stormwater Management Strategies

Hydrologic and sediment transport modeling were used to examine the effectiveness of typical stormwater management policies in reducing the potential for stream-channel erosion. Two bedload functions and three total-load transport relationships were applied to 8 mm gravel and 0.5 mm sand bed materials to compare the performance of the relationships in estimating detention requirements across modes of sediment transport. The various sediment-transport relationships yielded widely diverging estimates of sediment-transport capacity and yet suggested detention volume requirements that agreed within 20%. Detention design for control of cumulative sediment load required a detention storage volume 61% greater than a peak control detention facility and resulted in an altered temporal distribution of sub-bank-full shear stress. Design of stormwater facilities based on time-integrated sediment-transport capacity may inadvertently result in channel instability and substrate changes unless the approach accounts for the frequency distribution of sub-bank-full flows, the capacity to transport heterogeneous bed and bank materials, and potential shifts in inflowing sediment loads.