MODELING STORM-DRIVEN WAVE RUNUP FOR USE IN FORECASTS OF COASTAL GEOMORPHIC CHANGE DURING HURRICANES

Hurricanes can cause extreme changes to coastal topography, including the destruction of protective dunes, the creation of large overwash deposits, and the opening of new inlets. These changes have a profound impact on coastal environments and may increase vulnerability to future storms. The type and magnitude of barrier island response to storms is dependent, in part, on the interactions between beach morphology and the oceanographic forces associated with waves and storm surge. The shoreline manifestation of these forces includes wave runup, which is often an ignored contribution to hurricane-induced water levels. For a range of typical beach and wave conditions, the elevation of wave runup, as well as its components swash and setup, can be estimated from offshore wave height, wave period, and a local beach slope using empirical parameterizations (Stockdon and others, 2006). However, extending these runup predictions to accurately cope with extreme storm conditions requires new modeling approaches.

Because observations of runup during extreme wave events are often unavailable, a numerical model (Xbeach) was used to simulate wave-group generated surf and swash motions during storms. Extensive comparisons between modeled, parameterized, and observed runup at the U.S. Army Corps of Engineers Field Research Facility in Duck, North Carolina, reveal systematic differences between modeled and observed runup. Characterizing these differences allows modeled data to be used to extend the application of the empirical runup formulation to storm conditions. This will result in improved predictions of coastal erosion due to future hurricanes and other extreme storms.

References cited: Stockdon, H.F., Holman, R.A., Howd, P.A. and Sallenger, A.H., 2006. Empirical parameterization of setup, swash, and runup. Coastal Engineering, 53(7): 573-588.