Storm Drain Effects on Urban Flooding

Urban flooding is a primary concern in all developed areas. Understanding what factors contribute to the magnitude and frequency of flooding is of primary importance when designing an engineering system to mitigate flooding. To understand the effect of impervious area versus the role of the storm drainage system in urban flooding, the U.S. Army Corps of Engineers Gridded Surface Subsurface Hydrologic Analysis model was enhanced with a subsurface drainage model. The subsurface drainage model is described and an example application in Maryland of an urban area demonstrated that the storm drainage system plays a major role in the hydrologic response of a watershed to moderate-to-high rainfall events. Due to the under-capacity of the storm drainage system, however, the effect of the storm drainage network for extreme rainfall events is greatly diminished. Forward and Acknowledgments. Much of the storm drainage model development and theory is taken directly from Ji (1998). The applications section was taken largely from Jonathan Zahner’s M.S. thesis (Zahner 2004), and is provided as an example. Introduction. There is no argument that flood magnitude and frequency increase as urban development spreads throughout a watershed. It is obvious that understanding this trend is of great social and economic importance but what causes this change in hydrology is the source of much debate and numerous studies. Changes in urban runoff volume and flood peaks have been blamed historically on increases in impervious area. This theory was recently challenged by a study in and around Charlotte, North Carolina (Smith et al. 2002). The conclusion by Smith et al. (2002) was that the increase in storm drainage connectivity and hence hydraulic efficiency played the greatest role in increasing flood magnitudes. The inability to explicitly simulate storm drainage networks is seen as a major limitation in the application of GSSHA to urbanized areas. To address this issue, the SUPERLINK (Ji 1998) storm drainage scheme was added to GSSHA (Zahner 2004). SUPERLINK BACKGROUND. A complete review of the literature was undertaken to find a robust method that would allow integration with the advanced features of GSSHA. The USGS Full Equations (FEQ) model (Franz et al. 1997), U.S. National Weather Service DWOPER (Lewis et al. 1996), SWMM (Rossman et al. 2004), Danish Hydraulics Institute MOUSE (Gustafsson et al. 1999), and the SUPERLINK scheme (Ji 1998) were all evaluated. For a more ERDC TN-SWWRP-12-1 August 2012 Storm Drain Effects on Urban Flooding by Fred L. Ogden, Ph.D., P. E., Justin M. Niedzialek, Ph.D., and Aaron R. Byrd, P. E. Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE AUG 2012 2. REPORT TYPE 3. DATES COVERED 00-00-2012 to 00-00-2012 4. TITLE AND SUBTITLE Storm Drain Effects on Urban Flooding 5a. CONTRACT NUMBER