Estimating storm-induced wave runup using numerical and parameterized models

Wave runup during storm conditions can drive extreme changes to coastal environments. Prediction of runup elevation during these events is important for identifying areas at risk to erosion and coastal flooding and for evaluating potential hazards to coastal communities. Parametric models are often used to calculate runup levels that are expected from specific storms or storm scenarios. However, most parameterizations were not developed or tested under highly energetic conditions, principally because observations of runup under these conditions are extremely difficult to collect. Therefore, we used a numerical model, XBeach, to simulate runup during storm conditions and then, using these model-generated data, determine where an existing parameterization (Stockdon et al, 2006) can be extended or modified.

First, the accuracy of XBeach-simulated wave runup components (setup and swash) were evaluated using observations collected during the 1997 SandyDuck field experiment in North Carolina. The swash component was split into incident band and infragravity band. Incident-band swash is not modeled explicitly by XBeach and therefore simulated values are significantly lower than observations. Setup and infragravity swash are adequately modeled using XBeach, indicating that these simulated storm-induced water levels can be used as surrogates for actual observations. Generalized wave conditions for category 1-5 hurricanes were then used to model extreme setup and swash. For setup, simulated hurricane results are higher than what would be predicted using the parameterization. Here, interaction of high water levels with the dune face prevents a simple extrapolation of the existing parameterization. XBeach-modeled infragravity swash for hurricane conditions compares well with the parameterization suggesting that we can use simulated data to extend this parameterization to more extreme wave conditions.