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Title: OBSERVED EROSION PROCESSES DURING EMBANKMENT OVERTOPPING TESTS

Author
item Hanson, Gregory
item Cook, Kevin
item HAHN, WILL - HDR ENGINEERING INC
item Hunt, Sherry

Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2003
Publication Date: 7/30/2003
Citation: HANSON, G.J., COOK, K.R., HAHN, W., BRITTON, S.L. OBSERVED EROSION PROCESSES DURING EMBANKMENT OVERTOPPING TESTS. 2003. AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. Paper No. 03-2066.

Interpretive Summary: Even though the occurrence and effects of water flowing over the top of earthen embankments by rising floodwaters are rare, the impact to people and property downstream of such an embankment is important to engineers, and planners alike, who must evaluate the hazards of local flooding. There are about 57,000 dams on the national dam inventory that have the potential for overtopping. The USDA-ARS has conducted 7 large-scale overtopping failure tests on embankments. The objectives of this paper are to describe the observed breach erosion processes from these tests, and to compare results with historical cases. The erosion process is observed to be a four-stage process with steps and water-falls observed to be an important part of the erosion process during overtopping. The rates of erosion are observed to vary several hundreds of times, depending on soil materials. The test results are compared with historical cases and help explain case history observations related to the opening size in failed embankments. Understanding these erosion processes during embankment overtopping is important to predicting the impacts on local communities and surrounding areas affected by the resulting flood.

Technical Abstract: Dam embankment erosion and breaching from overtopping events is important to both engineers and planners alike. The timing and erosion process of a dam embankment breach, due to flood overtopping, can dramatically impact the rate that water is released from a reservoir. This rate of water released, directly impacts the hazard to life and property downstream of a breached dam. The USDA-ARS has conducted 7 large-scale overtopping failure tests on embankments constructed of cohesive materials. The objectives of this paper are to describe the observed breach erosion processes from the 7 tests, and to compare results with dimensionless parameters from historical cases. The erosion process is observed to be a four-stage process with headcut erosion observed to be an important part of the erosion process of cohesive embankments during overtopping. The headcut migration rate and erosion widening rates are observed to vary by orders of magnitude, depending on soil materials. The test results appear to scale with historical cases and the relationship of headcut migration rates and erosion widening rates help explain the observed maximum breach widths from historical cases. Understanding the erosion processes during embankment overtopping is important to predicting the impacts on local communities and surrounding areas affected by the resulting flood.