A Model of Surface Fine Grained Laminae, Streambed and Streambank Processes Applicable to the Watershed Scale

The sediment transport and biological processes governing the fate and transport of the surface fine grained laminae (SFGL) has not been included in models seeking answers at the watershed scale. In this model development, the flow is used to drive the sediment transport continuity model which includes subroutines for fluvial erosion based on excess shear stress for cohesive sediment sources, i.e., SFGL, bed and bank, transport based on the residual transport capacity concept coupled with traditional deposition and sediment routing, and SFGL fate including biofilm generation and bioturbation of consolidated bed sediments. The model is applied to a lowland watershed in a conceptual watershed modeling framework. The model is calibrated for a stream reach in the watershed using concentration and flow data at the watershed outlet and from the tributaries that are used to calculate sediment flux using Einstein's approach. In addition, the critical shear stress, erodibility coefficient, and biological terms are parameterized based on literature reported values. The importance of small and moderate flow events to downcutting of the streambed and large events for deposition to the bed is found for the stream. Biological activity and bioturbation in the SFGL continue over time to develop eroded bed material. In this manner, biological rates can be seen as important for assessing geomorphologic rates on long time-scales.