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Title: PERFORMANCE OF BARE EARTH AND VEGETATED STEEP CHANNELS UNDER LONG DURATION FLOWS

Author
item Hanson, Gregory
item Temple, Darrel

Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Other
Publication Acceptance Date: 8/1/2001
Publication Date: 8/1/2001
Citation: Hanson, G.J., Temple, D.M. 2001. Performance of bare earth and vegetated steep channels under long duration flows. American Society of Agricultural Engineers Meetings Paper No. 01012157.

Interpretive Summary:

Technical Abstract: Interest in the occurrence and effects of water flowing over the top of earthen embankments by rising floodwaters has existed for years. Even though dam overtopping failures are rare, the impact to people and property downstream of a reservoir is important to engineers and planners alike, who must evaluate the hazards of local flooding. Research is presently underway ywith the goal of providing a means of evaluating the performance of overtopped earth embankment dams protected only by a vegetal cover. Recent outdoor laboratory studies on steep sloped (33%) trapezoidal channels have been conducted on a 3-m high constructed earthen embankment. The embankment was constructed of a silty sand material. The channels are 6 m long, and 1 m wide, with 1-to-1 side slopes. Contrasting tests, two vegetated and two non-vegetated, were conducted. The tests were conducted for 75 hours of continuous flow in the vegetated channels and for 52 hours and 73 hours in the non-vegetated channels. Maximum erosion rates were observed to be 25 t 50 times greater in the non-vegetated channels. The maximum observed erosion rate was 0.030 m/h in the non-vegetated state. The erodibility determined from the hydraulic stress analysis was comparable to the erodibility determined from laboratory jet tests. Maximum erosion occurred at the toe of the slope in the vegetated channels and at the upstream end of the slope in the non-vegetated channels. The non-vegetated channels eroded in a classical stair stepped fashion with overfalls and plunge pools. These studies add insight into the nature of embankment overtopping erosion and failure in the initial phases of erosion. These observations will be essential in updating earthen embankment failure models and adding to the safety and well being of people and property.