Citation

Hanson GJ, Temple DM. Trans. ASAE/ASABE 2002; 45(3): 695-701.

Copyright

(Copyright © 2002, American Society of Agricultural and Biological Engineers)

DOI

unavailable

PMID

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Abstract

Thousands of dams built in the U.S. have a potential to be overtopped by flood flows. It is therefore necessary to understand the mechanics of embankment erosion in order to evaluate the potential erosion damage to an embankment and the safety risk that overtopping represents. This article describes tests conducted at the USDA-ARS Hydraulic Engineering Research Laboratory in Stillwater, Oklahoma, using an embankment 3 m high and 37 m long with 3:1 slopes. Measured water surface, bed, and velocity profiles and predicted hydraulic stress for four 1-m wide trapezoidal channels, two vegetated and two non-vegetated, are compared. The tests were conducted at discharges of 0.2 m3/s and 0.6 m3/s. The tests in the vegetated condition were run for 75 hours, and the tests in the non-vegetated condition for 73 hours and 52 hours, respectively. The maximum average erosion rate in the non-vegetated channels was 25 and 50 times greater than that in the vegetated channels for the two flows. The erosion in the non-vegetated channels was not uniform spatially along the length of the channel or temporally over the duration of the tests. The erosion progressed into stair-stepped overfalls. Jet test analysis of laboratory soil samples indicated that erosion resistance varied up to 3 orders of magnitude due to variations in compaction, percent saturation, and density. The excess stress parameters, erodibility coefficient (kd) and critical stress (τc), based on post-test samples, were predicted to be 0.00029 m/Pa-h and 0.55 Pa, respectively. Hydraulic stress evaluation of the two bare-earth soil channels over the duration of the tests resulted in kd values of 0.00026 and 0.00029 m/Pa-h for the tests conducted at discharges of 0.2 m3/s and 0.6 m3/s, respectively. Evaluation of the two vegetated channels resulted in kd values of 0.00070 and 0.00004 m/Pa-h. It is anticipated that the results of these studies will provide the basis for improved evaluation of the erosion of embankments subjected to overtopping. This study will provide a tool for evaluating dam rehabilitation needs, as well as for assessing the risk to human and livestock life and property loss downstream.