Number of points in cumulative rainfall distribution N pĭimensionless cumulative time for rainfall distribution T *ĭimensionless cumulative depth for rainfall distribution D * The catchment is an open book, with runoff from one (or two) plane(s) draining laterally into a (central) channel, the latter draining into the catchment outlet.īoth SI and U.S. The models were tested by specifying a common input data set consisting of storm type, catchment characteristics, hydrologic abstraction, and relevant hydraulic parameters. Army Corps of Engineers, Davis, California. HEC-HMS, developed by the Hydrologic Engineering Center, U.S. Victor Miguel Ponce of San Diego State University, San Diego, California. In this article, we compare three overland flow models: The spatial and temporal description leads to differential equations and to their solution by numerical means.
#Epa swmm different from pcswmm output free#
The theory is based on established principles of fluid mechanics such as laminar and turbulent flow, mass and momentum conservation, and unsteady free surface flow. Overland flow theory uses deterministic methods to describe surface runoff in overland flow planes. This type of flow is the first manifestation of surface runoff, since the latter occurs first as overland flow before it has a chance to flow into channels and become streamflow. Overland flow is surface runoff that occurs in the form of sheet flow on the land surface without concentrating in clearly defined channels. Given the importance of these models in hydrologic engineering practice, more research is needed to clarify the issues raised in this article. Much higher than expected assuming uniform abstraction. SWMM and HEC-HMS behaved more or less properly for the impervious cases (a and c), with some imperfections.įor case b, due to the initial abstraction assumed, SWMM and HEC-HMS showed a peak flow Results for peak flow, timing of the peak, and mass conservation were as expected. ONLINEOVERLAND behaved properly for the three cases. The results were analyzed for (1) peak flow, (2) timing of the peak, and (3) mass conservation. (c) Modified impervious case, with CN = 100, and P = 17.7666 cm. (b) Pervious case, with CN = 80, P = 24 cm and, consequently,Įffective precipitation P e = 17.7666 cm (a) Impervious case, with curve number CN = 100, and total precipitation P = P e = 24 cm Three overland models, ONLINEOVERLAND, SWMM, and HEC-HMS were tested under three cases: