Evaluation of Erosion Rate of Coarse-Grained Materials Using a New Lidar Technology

摘要

Erosion rate of soils during a levee or dam overtopping event is a major component in risk assessment evaluation of breach time and downstream consequences. The mechanism and evolution of dam or levee breach caused by overtopping erosion is a complicated process and difficult to measure during overflow due to accessibility and quickly changing conditions. In this paper, the results from flume erosion tests are presented and discussed. The tests were conducted in a 1-m (3-ft) wide flume on four gravel mixes with a median grain size D_(50) of 5 mm and varying fines content. Each soil sample is prepared by compacting the soil mix near maximum dry density and optimum water content in a box embedded in the flume floor. The box measured 0.45 m wide × 1.2 m long × 0.18m deep. A shallow water lidar (SWL) system is utilized to record the evolution of soil erodibility and water depth along the scanned profiles of the test box parallel to the direction of the flow. SWL is a noncontact system that transmits laser pulses from above the water and records the time-delay between top and bottom reflections. Results from the SWL scans indicated that the erosion rate reduces significantly over the duration of the test. This is due to the changes in the hydraulic loading, and also due to the effect of the fines content and large particle size of the mix. Higher fines and clay content results in a lower initial erosion rate, while larger maximum particle size results in a lower erosion rate at the same acting bed shear.