Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2006
Publication Date: 8/3/2006
Citation: Wilson, G.V., Periketi, R., Fox, G., Dabney, S.M., Shields Jr, F.D., Cullum, R.F. 2006. Soil properties controlling seepage erosion contributions to streambank failure. Earth Surface Processes and Landforms 32, 447-459 (2007). doi: 10.1002/esp. 1405. Interpretive Summary: A large source of sediment in streams is from the banks of the streams themselves. Streambanks commonly have soil layers of different texture and permeability. Seepage out of a permeable layer can result in erosion of the layer, by a process called seepage erosion. Under-cutting of a streambank by seepage erosion can cause collapse failure of the bank. The objective of this study was to determine the impact of soil properties on seepage erosion and streambank failure. Flow through seeps and sediment concentrations were measured at eight locations along the banks of a stream in northern Mississippi. Using field observations as a guide, the soil layers of a shallow (45 cm) streambank, consisting of a 30 cm top soil, 10 cm permeable layer, and 5 cm impermeable layer, were reproduced in laboratory experiments to measure the soil-water properties controlling seepage erosion and bank failure. The time at which flow began and the rate of flow were related to the slope of the impermeable layer. Seepage erosion began within minutes of flow starting and undercut the banks by 7 to 20 cm. Sediment concentrations of seeps along the stream and in the laboratory experiments were extremely high. The sediment concentrations were related to the slope. These findings indicate the importance of detailed site characterization and the need to control the flow of water through permeable layers.
Technical Abstract: Up to 85% of the sediment leaving some watersheds may be from streambank failure. Seepage erosion of unconsolidated sand above a restrictive layer is an important erosion process in incised streams. The objective of this study was to determine the impact of soil properties on seepage erosion and the resulting streambank failure. Seepage flow and sediment concentrations were measured in situ at eight locations along the banks of a deeply incised stream in northern Mississippi. Using field observations as a guide, the soil profile conditions of a shallow (45 cm) streambank, consisting of a 30 cm top soil, 10 cm conductive layer, and 5 cm restrictive layer, were mimicked in laboratory lysimeter experiments to quantify the hydrologic properties controlling seepage erosion and bank failure under a 40 cm head. The time to flow initiation and the flow rate were linearly related to the slope of the restrictive layer. Seepage erosion began within minutes of flow initiation and resulted in substantial (7 to 20 cm) undercutting of the bank. Sediment concentrations of seeps were as high as 660 g L-1 in situ and 4500 g L-1 in the lysimeters. The sediment concentrations were related to the slope, thereby indicating the importance of detailed site characterization.