PHYSICAL MODELING OF OVERTOPPING EROSION AND BREACH FORMATION OF COHESIVE EMBANKMENTS

The formation process and timing of a dam embankment breach caused by flood overtopping can dramaticallyimpact the rate at which water is released from a reservoir and directly impacts the hazard to life and property downstreamof a breached dam. Therefore, dam embankment erosion processes and the rate of breaching from overtopping events areimportant to both engineers and planners alike, who must predict impacts on local communities and surrounding areasaffected by flooding. There is a distinct difference between the erosion processes of non-cohesive and cohesive embankmentsduring overtopping. The USDA-ARS has conducted seven large-scale overtopping failure tests on cohesive embankmentsranging in height from 1.5 to 2.3 m. The purpose of this study is to: (1) establish a better understanding of the erosion processof overtopped cohesive embankments, and (2) provide detailed data for future numerical model development, validation,calibration, and testing. Three soils were tested, two non-plastic SM silty sand materials and a CL lean clay. A four-stagebreach erosion process was observed for cohesive embankments. The primary erosion processes observed and reported in thisarticle for cohesive embankments during stages 2 and 3 were headcut migration and erosion widening. The rate of these twoprocesses was observed to vary by several orders of magnitude and was observed to be strongly dependent on the soil materialproperties.