WAVE RUNUP ON DIKES AND BEACHES

Abstract

In the United States, the Federal Emergency Management Agency (FEMA) is in the process of updating its coastal flood risk maps in order to determine which locations are threatened by storm surge and wave action. These maps require the prediction of extreme wave runup. A method for predicting the runup height along the entire coast must be robust, reliable, and applicable to many different coastal features. Kobayashi et al. (2008) developed a time-average probabilistic model that predicts wave runup statistics instead of the time series of shoreline elevation. This numerical cross-shore model, CSHORE, is extended to the wet-dry zone above the still water level to predict irregular wave runup on impermeable dikes and gentle impermeable slopes. To show the CSHORE’s capability in predicting runup on beaches with different geometries, the computed results from the model are compared to measured data from a variety of experiments. CSHORE is tested against 40 wave runup tests on an impermeable dike on a barred beach, 97 wave runup tests on an impermeable dike with a gently sloping beach, and 120 tests for wave runup on gentle uniform slopes. The measured 2% and 1% exceedence runup heights are predicted within errors of about 20%. The spectral significant wave height, Hmo, and a representative period are used for input to CSHORE.
The measured and computed cross-shore variations of Hmo are also computed and compared to measured data to show the capabilities and limitations of CSHORE in regards to predicting to wave transformation. Both the spectral period, Tm-1,0, and the peak period Tp at x = 0 are adapted as representative periods used in CSHORE to assess the period effect in CSHORE. The tested CSHORE is ready for practical applications such as FEMA’s coastal flood mapping, and is a good practical choice because it can be used to predict beach and dune profile changes.