COASTAL FLOODING & SOLUTIONS, Workshop July 2020
USGS Forecast of Total Water Level and Coastal Change Hazards along the U.S. East Coast
U.S. East Coast
Alfredo L. Aretxabaleta
U.S. Geological Survey, Woods Hole Coastal and Marine Science Center, Woods Hole, MA, USA.
The U.S. Geological Survey (USGS) provides reliable information in preparation for and in response to extreme storm events that is valuable to coastal communities, emergency managers, and local/State/Federal partners. Information is primarily presented through two main systems: the USGS Coastal Change Hazard Portal (https://marine.usgs.gov/coastalchangehazardsportal/) and the Total Water Level (TWL) and Coastal Change Forecast viewer (https://coastal.er.usgs.gov/hurricanes/research/twlviewer/).
The Coastal Change Hazard Portal provides historical shoreline change rates, coastal change predictions of near real-time storm events and storm-scenarios, as well as long-term shoreline change projections due to sea-level rise. The coastal change information provides probabilities of erosion during extreme storm conditions. Beach and dune profiles are compared to water levels (tides, surge, and waves) during hurricane and nor’easters to determine probabilities of collision, overwash, and inundation. Shoreline evolution in response to sea-level rise (SLR) is considered through three metrics: 1) the coastal vulnerability index that provides relative coastal susceptibility to SLR; 2) a Bayesian probabilistic assessment of shoreline change that incorporates multiple forcing and historical variables; and 3) the coastal response likelihood that differentiates static (e.g., inundation) and dynamic (e.g., landscape change, shoreline retreat) coastal responses.
The Total Water Level and Coastal Change Forecast viewer provides a continuous operational forecast of the combined effect of tide, surge, and wave runup along the coast. Tidal and subtidal (surge) water level forecasts are extracted from NOAA/NCEP’s Extratropical Surge and Tide Operations Forecast Systems. Wave characteristics (significant wave height and peak period) are obtained from the Nearshore Wave Prediction System (NOAA/NWS). Wave runup (setup and swash) is empirically estimated using the Stockdon et al. (2006) formulation informed by wave parameters and beach slopes derived from multiple lidar surveys. Then, the combined time-varying TWL is compared to beach and dune profiles along sandy coastlines, as in the portal case, to evaluate the potential for coastal change (probability of collision, overwash, and inundation). Validation of TWL is regularly conducted through comparisons with coastal cameras in available locations and with the short-term network of USGS gages (Surge, Wave, and Tide Hydrodynamics (SWaTH) Network) deployed during extreme flooding events (https://stn.wim.usgs.gov/FEV/). The TWL viewer delivers detailed forecasts of total water level and coastal change to regional weather offices and local and state decision-makers.
The combination of forecast and scenario-based products delivers guidance on potential coastal erosion and flooding hazards along the U.S. East Coast. These products continue to be evaluated through comparison with available observations, updated when new storms and/or SLR rates are available, improved to incorporate newer methodologies and data, and expanded to other regions.
The production and delivery of consistent forecast and scenario-based predictions and projections of coastal change.
Collaboration with other groups to avoid duplicate efforts and work together toward a common goal