Presenter: Sharifa Karwandyar (U.S. Geological Survey)

Description:
The Total Water Level & Coastal Change (TWL&CC) Forecast Model (https://coastal.er.usgs.gov/hurricanes/research/twlviewer/) is the outcome of a joint effort by the U.S. Geological Survey and the National Oceanic Atmospheric Administration and is the only national-scale water level model. The model provides multi-day forecasts along more than 4,700 km of sandy U.S. coastline. In this work, we assess forecast skill and uncertainties associated with the static, single estimate of beach slope presently included in the model. Forecasts of total water level elevations include tide and subtidal water levels, surge, and wave-induced runup. The Stockdon equation, which is included as wave-induced runup in the total water level estimation, can determine dune and beach erosion as wave energy dissipates in the surf zone. The extreme 2% exceedance value of runup is defined as R2 = <η> + S/2, where η represents setup and S includes infragravity and incident swash. The static beach slope is estimated by temporally averaging over all available lidar surveys for a model output location and spatially averaged over a 400 m window. At Madeira Beach, FL, imagery from a USGS CoastCam is used to estimate the time-dependent foreshore slope . The beach slope is estimated by mapping the intertidal beach profile by applying alongside shoreline detection algorithms at various tidal stages and applying a linear regression to daily observations. Observed beach slopes will be compared with the mean beach slope used in the TWL&CC model, and the influence on the accuracy of the predictions is assessed.