An unsteady flow hydraulic problem of considerable interest is the analysis of dambreaks and their downstream hydrograph. In this section, the main objective is to evaluate the diffusion form of the flow equations for the estimation of flood depths (and the flood plain) resulting from a specified dambreak hydrograph. The dambreak failure mode is not considered in this section. Rather, the dambreak failure mode may be included as part of the model solution (such as for a sudden breach) or specified as a reservoir outflow hydrograph.
The use of numerical methods to approximately solve the flow equations for the propagation of a flood wave due to an earthen dam failure has been the subject of several studies reported in the literature. Generally, the flow is modeled using the onedimensional equation wherever there is no significant lateral variation in the flow. Land (1980a,b) examines four such dambreak models in his prediction of flooding levels and flood wave travel time, and compares the results against observed dam failure information. In dambreak analysis, an assumed dambreak failure mode (which may be part of the solution) is used to develop an inflow hydrograph to the downstream flood plain. Consequently, it is noted that a considerable sensitivity in modeling results is attributed to the dambreak failure rate assumptions. Ponce and Tsivoglou (1981) examine the gradual failure of an earthen embankment (caused by an overtopping flooding event) and present detailed analysis for each part of the total system: sediment transport, unsteady channel hydraulics, and earth embankment failure.

