The National Weather Service (NWS) developed a simplified procedure 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, and technical expertise required in employing more highly sophisticated unsteady flow routing models such as the NWS FLDWAV model. With a minimal amount of data, The SMPDBK model can be used to predict the dam-break flood wave peak flows, peak flood elevations, and peak travel times at selected downstream points. This capacity for providing results quickly and efficiently makes the NWS SMPDBK model a useful forecasting tool in a dam failure emergency when warning response time is short and data are sparse.  The NWS SMPDBK model is also 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.

Three steps make up the procedure used in the SMPDBK model, These are: (1) calculation of the peak outflow at the dam using the temporal and geometrical description of the breach and the reservoir volume; (2) approximation of the channel downstream of the dam as a prismatic channel, including the effects of the off-channel (dead) storage where appropriate; and (3) calculation of dimensionless peak-flow routing parameters used with families of dimensionless routing curves, developed using the NWS DAMBRK model, to determine the peak flow at specified cross sections downstream of the dam.  These steps retain the critical deterministic components of the numerical NWS DAMBRK model.

The original FORTRAN code was developed in 1983 and revised in 1991. The current Java GUI replaces the awkward Fortran-based GUI while continuing to use the original FORTRAN calculations portion of NWS SMPDBK.  Although NWS discontinued support for the model in 2005, Janice Sylvestre has continued the development, maintenance, and support of the SMPDBK model.  The name of the model was changed to SDB since the continued work is not affiliated with NWS.

Limitation: SMPDBK does not account for backwater effects caused by natural or man-made channel constrictions (e.g., dams, bridges), the presence of which can substantially reduce SMPDBK’s accuracy.

Application: SDB-J was applied to the 2004 Big Bay Lake Dam failure in Mississippi.  The presentation below provides guidance on how to use SDB-J for an emergency dam failure analysis.