Spatial Discretization of Large Urban Watersheds

The construction of rainfall-runoff models represents one of the most complex and challenging problems in water resources engineering. This is particularly true for urban watersheds in which, the entire watershed is discretized in smaller sub-basins and additional systems need to be modeled such as the drainage network. With the advantage of computer systems, such as GIS, it has been possible to obtain physical features of large and complex urban areas. Then, this information is used to build rainfall-runoff models such as, EPA-SWMM. Even when applications have been made in small urban watersheds, there is no a methodology to follow for big areas (larger than 3 mi²). Recommendations are given to discretize urban watersheds based upon hydrological and morphological watershed features. Modeling suggestions are given, for example, estimating the runoff length and then, computing the width would yield to more accurate results. Also, since it is complex to model the entire drainage network, simplifications should be made to obtain an equivalent drainage network. Finally, the proposed methodology was tested and compared with USGS streamflow records in three urban watersheds in North Carolina.