Dynamic Flow Resistance for Hydrologic Simulations

The SEDLAB simulation model, which represents overland runoff and erosion from agricultural watersheds, has been revised to include dynamic overland and channel flow resistances, new infiltration methods, and improved sediment transport equations. Two parameters which represent overland and channel flow resistance in the simulation model were calibrated from event data on W-1 near Treynor, Iowa, and related to observed roughness features on the watershed. These parameters were found to change in a manner which represented the event-to-event variation in flow resistance due to tillage, rill development, and changes in residue, crop, and vegetative cover. The methods and parameters developed on watershed W-1 to represent flow resistance were applied to events on adjacent W-2 near Treynor, Iowa, with good results. The flow resistance parameters determined in this study are representative of watersheds with loessial soil, contoured fields, and a corn crop. Further testing on other agricultural watersheds is needed to define the dynamic variations of flow resistance caused by antecedent rainfall, runoff, crop, and land management.