Including Empirical Wave Runup in an Operational Forecast Model for Coastal Water Levels

Water levels along the coast during storms are comprised of a combination of astronomical tides, storm surge, and wave-induced setup and swash processes. The wave component can be responsible for more than half of the total water level elevation along the coast during large wave events, but this element is absent from existing real-time meteorological and oceanographic forecast systems (Sullivan and Uccellini, 2013). While parameterized wave runup models are coupled with oceanographic models to predict coastal vulnerability to extreme events (e.g. Stockdon et al. 2013), they are static models that predict the water level expected during the storm based on the maximum predicted wave height and surge without considering the time-varying characteristics. In addition, the forecasts using these models have typically been initiated during tropical storms, missing severe flooding impacts that can occur during other storms (e.g. nor'easters) when large waves coincide with high tides. During these events, sand dunes and roads can be overwashed even when storm surge is considered minimal. Without operational, time-varying predictions of total water levels that include the magnitude and timing of all processes, communities lack warning and preparation for such events. The National Oceanic and Atmospheric Administration (NOAA) and the U.S. Geological Survey (USGS) have partnered to create an operational modeling system that simulates tides, storm surge, wave transformation and wave runup along coastal areas to predict total water elevations.

The model is currently being implemented and tested at two pilot locations: Duck, North Carolina and Treasure Island, Florida with the intention of rolling it out to other NOAA Weather Forecast Offices in future years. Tides and subtidal water levels are provided by the Extratropical Surge and Tide Operations Forecast Systems (ESTOFS) and wave heights and periods are being predicted using the Nearshore Wave Prediction System (NWPS; Van der Westhuysen et al., 2013). Wave properties are output along the 20-meter contour and provide input for the empirical wave runup model developed by Stockdon et al. 2006. Beach slopes, also required by the wave runup model, are calculated by the USGS using lidar topographic data. The spatial and temporal uncertainty in total water level is also predicted. Both pilot sites will be instrumented with video remote sensing equipment to provide observations of total water levels for comparison.