Numerical simulation of the flow over a coastal structure in depth-limited conditions

Abstract

A one-dimensional time-dependent numerical model was used to simulate the flow over a coastal structure in depth-limited conditions. Two different laboratory data sets were used to compare with the model predictions. The first data set consists of detailed measurements of irregular wave transformation in front of the structure in depth-limited conditions. The second data set consists of several test runs to study the irregular wave reflection and runup on the coastal structure in depth-limited conditions. Three methods to separate the incident and reflected wave elevations were discussed and compared to determine which method is the most realistic to be used in this research. The three wave gage method which used measured wave elevations at three different spatial locations was compared with the co-located gages methods which used the measured horizontal velocity and wave elevation time series, or the measured horizontal and vertical velocities time series. The comparisons showed that the three wave gage method gave a more realistic result compared to the two co-located gages method. Comparison of the model predictions with the laboratory measurements showed that the numerical model underpredicted the incident wave heights and overpredicted the reflection and runup heights. The computed runup was shown to be less sensitive to the specified friction factors. Reduction of the friction factor gave a better pre- diction of the exceedance probability of the runup height, although smaller friction factor tends to make the numerical model more unstable.