A National System for Threshold Runoff Estimation

by Konstantine P. Georgakakos, Univ of Iowa, Iowa, United States,
Theresa M. Carpenter, Univ of Iowa, Iowa, United States,
James A. Cramer, Univ of Iowa, Iowa, United States,
Jason A. Sperfslage, Univ of Iowa, Iowa, United States,
Timothy L. Sweeney, Univ of Iowa, Iowa, United States,
Dan L. Fread, Univ of Iowa, Iowa, United States,



Document Type: Proceeding Paper

Part of: Engineering Hydrology

Abstract: Threshold runoff is the amount of effective (or excess) rainfall of a given duration uniformly distributed over a certain catchment that is just enough to cause flooding at the outlet of the draining stream. Threshold runoff estimates, when used in conjunction with operational soil moisture accounting models and radar rainfall data, are an essential component of a flash flood warning system. Threshold runoff estimates can be determined by equating the peak catchment runoff, as computed from the catchment unit hydrograph of the given duration, to the stream flow at the catchment outlet at the time of flooding. Geographic Information Systems (GIS) and distributed terrain elevation data bases have been used to support the application of the aforementioned hydrologic/hydraulic principle to natural flash-flood prone catchments on a regional scale. The software package threshR has been developed to determine threshold runoff estimates without manual intervention. Snyder's unit hydrograph and a geomorphologic unit hydrograph have been used as options to determine the catchment peak runoff rate. Manning's steady, uniform flow resistance formula and the two-year return period flow have been used as options to determine the flood flow at the outlet of the draining stream. To a large extent use of any permutation of the aforementioned options depends on available data. Results of error analysis are presented that show the accuracy of catchment delineation by the GIS software, and the accuracy of the threshR threshold runoff estimates as compared to those computed manually using existing unit hydrographs of selected catchments.

Subject Headings: Runoff | Geographic information systems | Catchments | Disaster warning systems | Floods | Data processing | Hydrographs | Information systems

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