Thousands of dams built in the U.S. and around the world have a potential to be overtopped by flood flows. It is therefore necessary to understand the mechanics of embankment erosion due to overtopping in order to evaluate the potential erosion damage to an embankment and the safety risk that overtopping presents. Research is presently underway at the USDA-ARS-PSWCRL within the Research Hydraulic Engineering Unit to evaluate the performance of vegetated earth embankments subjected to overtopping.

The three-phase earth spillway erosion technology developed for the Natural Resources Conservation Service SITES software forms the point of beginning for this effort. Initial results of full scale overtopping tests suggest that it may be possible to extend this technology to the steeper slopes of earth embankments. The goal of the research effort is to predict the amount of allowable embankment overtopping that can be experienced without significant damage, the extent of overtopping required to breach a specific embankment, and the rate of breach development, or the breach hydrograph that may result from the breach.

The research effort presently underway utilizes a 10 ft high vegetated earth embankment to look at breach initiation, a reservoir and proto-type scale embankments to study breach erosion (Time lapse of Test 1, and Test 7) and a smaller rigid-boundary model to evaluate the head-discharge relations applicable to the anticipated breach geometry.

A Workshop on Issues, Resolutions, and Research Needs Related to Embankment Dam Failure Analysis, jointly sponsored by the USDA and the Federal Emergency Management Agency (FEMA) was held in Oklahoma City, OK June, 2001. This workshop brought together both U.S. and International engineers and scientists to determine needs related to embankment dam failure analysis. This workshop built upon the results of the International Dam Breach Processes Workshop, jointly sponsored by the Agricultural Research Service and the US Bureau of Reclamation, held in Stillwater, OK March, 1998. This workshop brought together engineers and scientists to discuss technology related to dam breach, including that related to overtopping of vegetated earth embankments.

For additional information contact Darrel Temple and Greg Hanson.

Watershed Flood Control Fact Sheet