Scour Problems and Methods for Prediction of Maximum Scour at Vertical Seawalls.

摘要

Laboratory experiments consisting of 22 tests were conducted in the 6-ft-wide wave flume at the US Army Engineer Coastal Engineering Research Center (CERC) to evaluate methods for estimating wave-induced scour depth (Sl) at vertical seawalls. Existing scour prediction methods range from rule-of-thumb estimates to semi-empirically derived equations. In the study, both regular and irregular waves were used to move sand with a mean diameter of 0.18 mm placed on the seaward side of a simulated vertical seawall. In the initial part of the study, 18 cases were run using irregular waves with various water depths, seawall locations relative to still-water level (swl), wave heights, and wave periods. All of the bottom profiles generated by the 18 irregular wave tests in the study supported a rule-of-thumb method, which states that maximum scour depth will be less than or equal to the incident unbroken deepwater wave height Ho, or S/Ho less than or equal to 1. When additional data from other studies (which used regular waves exclusively) were considered, the rule of thumb did not hold for all cases. To examine the effects of regular versus irregular waves in movable-bed laboratory studies, four additional test cases were run using regular waves having comparable water depths, wave heights, wave periods, and seawall locations relative to swl to four of the irregular wave test cases. In each of the four regular wave cases, scour depth exceeded scour depths associated with comparable irregular wave tests. On the average, scour depth increased by approximately 15 percent with regular water conditions.