Simple models to evaluate non-point pollution sources and controls

When selecting an algorithm for a non point source model, it is important to strike a balance between complexity and ease of use, so that the predictions can be made with the desired accuracy without requiring that the user become an expert hydrologist. In the development of SEDIMOT II, a design aid model for sediment control structures, an attempt was made to strike such a balance. SEDIMOT II is a distributed parameter model in which runoff and sediment yield are determined for each homogeneous subwatershed and routed downstream to structures and junctions. Runoff is determined with SCS curve number techniques utilizing unit hydrographs with differing shapes depending on land use. Channel routing is accomplished with Muskingum's method. Sediment yield is calculated with either the MUSLE or CREAMS equations. The time distribution is determined by a power relationship between sediment concentration and flow rate. The size distribution is determined by an algorithm which assumes that the larger particles are deposited first. Sediment routing through ponds is determined from either the DEPOSITS plug flow model or the more recent Continuous Stirred Tank Reactor in Series (CSTRS) model. Sediment routing through grass filters is calculated by the GRASSFIL model and through check dams by a combination of a water surface profile model and Camp's overflow rate model.