The National Weather Service (NWS) developed a procedure for predicting the breach parameters and the outflow hydrograph of an earthen dam. The procedure known as the Breach Erosion Model (BREACH) produces the size and shape of the dam breach opening, the time of formation, the outflow hydrograph, and the tailwater elevation hydrograph. The model is physically based on the principles of hydraulics, sediment transport, soil mechanics, the geometric and material properties of the dam, and the reservoir properties (storage volume, spillway characteristics, and the time-dependent reservoir inflow rate). The dam may be either man-made or naturally formed as a consequence of a landslide. The critical material properties of the dam are the internal friction angle, cohesive strength, and average grain size diameter (D50 ).
The parametric model uses empirical observations of previous dam failures such as the breach width-depth relation, time of breach formation, and depth of breach to develop the outflow hydrograph. The critical properties used by the model are measurable or can be estimated within a reasonable range from a qualitative description of the dam materials. However, it should be emphasized that, even if the properties can be measured, there is a range for their probable value, and within this range, outflow hydrographs of varying magnitude and shape will be produced by the model. The hydrologist or engineer should investigate the most critical combination of values for the dam’s material properties.
The original FORTRAN code was developed in 1984 by Dr. Danny Fread, and the last NWS release was in 1999. Although NWS ceased support for the model in 2005, Janice Sylvestre has continued the development, maintenance, and support of the BREACH model. The name of the model was changed to BRCH since the continued work is not affiliated with NWS.
A Java GUI (BRCH-J) is used to create or read in an input data file, run it through the BRCH application, display an animation of the dam breach formation, and display the hydrographs/rating curve graphically. The animation algorithm has been modified to better represent the assumptions made in the BRCH model. An example of the BRCH-J animation of a simulated piping failure of the 1976 Teton Dam breach is below.
