Modeling of Scour-Inducing Ice Effects at Melvin Price Lock and Dam

A numerical model was used to better understand ice-related scour processes at a large lock and dam. Large scour holes in front of Melvin Price Lock and Dam, the largest navigation structure on the Mississippi River, present a unique opportunity to explore this effect because the scour has been so severe and well documented. Likely scenarios for river ice accumulation and passage were identified based on historical flows and observations. For all simulations, the ice accumulated upstream of the gates as observed in the field and the ice thicknesses were found to match well with the general shape of the scour surveys. Ice thicknesses as large as 5.9 m and under-ice depth-averaged water velocities as great as 6.6 m/s were observed in the simulations. By using a shear stress criterion, the rock size necessary to prevent the scour exceeded the original rock size of 0.33 m for six of the seven cases. This study demonstrates that the presence of a localized thick ice accumulation increases the potential for bed shear and may cause movement of stone bed protection sized for open water conditions. Ice processes should therefore be considered in the design or rehabilitation of riprap protection at large lock and dam structures.