Net Transfer of Sediment from Floodplain to Channel on Three Southern U.S. Rivers

Abstract

Eroding streambanks play an important role in the transfer of fine sediment between temporary storage in a floodplain and active transport by a river. Quantifying this transfer rate is important both for developing sediment budgets for fine sediment and for describing of the fate of contaminants that are bound to sediment particles. Many studies have measured gross bank retreat rates without also measuring the volume of material deposited in point bars on the opposite accreting bank. However, the net transfer of material from a floodplain to a river channel cannot be computed without accounting for deposition in point bars. Since the local geometry and channel migration rate determine the net transfer at any given location, and since both of these vary in the streamwise direction, computing net transfer rates is more difficult than computing gross bank erosion rates. This study presents net transfer rates for portions of three U.S. rivers: a 91 km reach of the Pearl River in Louisiana, a 62 km reach of the Bogue Chitto River in Louisiana, and a 35 km reach of the Neuse River in North Carolina. Channel migration rates taken from sequences of historic aerial photographs, together with detailed topography obtained using LIDAR, allow both the local erosion rate from cut banks and the local deposition rate on point bars to be estimated approximately every half channel width down the channel. These rates are used to develop system-wide net transfer rates. The datasets can be used to optimize surveying strategies for measuring net transfer rates on streams where high-resolution digital elevation data does not exist.