Levee development along tidal channels

Levees are small elevation ridges found on the edge between channels and shoals. They are known to develop along river channels during floods and along channels in alluvial deep water fans. Levees in tidal environments such as the Waddenzee are less pronounced (with a typical height in the order of 10 cm) and may be recognized by the fact that they become dry earlier than the surrounding mudflats, due to their higher elevation and coarser material. Levees form an essential link in the morphological interaction between tidal channels and shoals, although their development is yet poorly understood and requires further research. We explore levee development by a process-based approach (Delft3D) both under highly schematized conditions and a realistic case study. The schematized approach concerns morphological development of a 2km long 100 m wide tidal channel with surrounding tidal flats. The levees develop during flood and further analysis shows the sensitivity to model parameters such as the diffusion coefficient, shoal width, grain size, and initial channel depth. The realistic case study concerns a tidal channel in a sub-embayment of San Francisco Estuary. 150 Years of bathymetric observations are coupled to a process-based morphodynamic modeling exercise explaining the levee development. Model results of the schematized setup and teh San Pablo Bay case have in common that major accreation of the levees and the channel slopes occurs during flooding conditions.