FLOOD06918 - Laserfiche WebLink

Home Browse Search

THE NWS SIMPLIFIED DAM BREAK FLOOD FORECASTING MODEL FOR DESK-TOP AND HAND-HELD MICROCOMPUTERS 1 Jonathan N. Wetmore and Danny L. Fread SYNOPSIS The National Weather Service (NWS) has developed a simplified procedure that utilizes desk-top or hand-held microcomputers for predicting downstream flooding produced by a dam failure. This procedure, known as the Simplified Dam Break (SMPDBK) Flood Forecasting Model, produces information needed for delineating areas endangered by dam break floodwaters while substantially reducing the amount of time, data, computer facilities, and technical expertise required in employing more highly sophisticated unsteady flow routing models. With only an inexpensive microcomputer and a minimal amount of data, the user may within minutes predict the dam break floodwave peak flows, depths, and travel times at selected downstream points. This capacity for providing results quickly and efficiently should make the SMPDBK model a useful forecasting tool in a dam failure emergency when warning response time is short, little data are available, and large computer facilities are inaccessible. However, the SMPDBK model should prove even more useful for "pre-event" dam failure analysis by emergency management personnel engaged in preparing disaster contingency plans when the use of other flood routing models is precluded by limited resources. , The SMPDBK model is designed for interactive use (i.e., the computer prompts the user for information on the dam, reservoir, and downstream channel and the user responds by entering the appropriate data values), and it allows the user to enter as much or as little data as are available, automatically using preprogrammed defaults when the response to a prompt indicates the data is not available. Using the internally set default values, SMPDBK is capable of producing approximate flood forecasts after reading in only the dam height, reservoir storage volume, and depth-vs.- width data for one cross-section of the downstream river valley (determined from on-site inspection or topographic maps). If however, the user has access to additional information (i.e., the reservoir surface area, estimates of the final width and depth of the breach, the time required for breach formation, the turbine/spillway/overtopping flow, the slope of the channel and the Manning roughness coefficient, flood depth (depth where flooding becomes a problem), and elevation-vs.-width data for up to five downstream channel cross-sections), the model will utilize this information to enhance the accuracy of the forecast. lResearch Hydrologist and Senior Research Hydrologist, Hydrologic Research Laboratory, Office of Hydrology, National Weather Service, NOAA, 8060 13th Street, Silver Spring, Maryland.