Evaluation of a linear bank erosion equation

Abstract

Field surveys and aerial photographs were used to measure the rate of migration of a bend of the Brandywine Creek near Chadds Ford, Pennsylvania. Velocities near the bank were measured in the field during high flows and also estimated by solving a form of the St. Venant equations. Engineering properties of the bank soils and the spatial density of trees growing along the bank were also measured. The data indicate that rates of bank migration are linearly related to the magnitude of the near‐bank velocity. If the St. Venant equations are used to estimate the near‐bank velocity, the data also suggest that erosion rates are proportional to u b ‐ U , where u b is the near‐bank velocity and U is the reach‐averaged velocity. In addition, rates of bank migration are reduced where the density of silver maples (Acer saccharinum) is high. Boxelder (Acer negundo) and white ash (Fraxinus americana) are also found along the bend, but these species do not noticeably influence rates of bank migration.