Changes to the Coastline Can Affect Where, and How Severely, Flooding Occurs

Part Two of a Six-Part Series Highlighting USGS Hurricane Science

By Communications and Publishing June 15, 2022

The 2022 Atlantic Hurricane Season runs from June 1 through November 30. Throughout the season, the U.S. Geological Survey will be providing science that can help guide efforts to protect lives and property if a storm threatens the U.S.

Hurricane Ida path — Screenshot of the Hurricane Ida coastal change forecast taken August 28, 2021. The colored lines indicate predicted probabilities of dune erosion (inner band), overwash (middle band), and inundation (outer band).

Sand dunes may not have a reputation for their sturdiness, but they are critical buffers protecting shorelines from hurricanes and tropical storms. When stormwaters erode, inundate, or wash away sand dunes during coastal storms the coastal communities, habitats and infrastructure behind the dunes become more exposed to possible flooding.

As a storm approaches land, USGS scientists forecast how it may reshape the coastline, and what that may mean for erosion and flooding impacts on coastal communities. They accomplish this with two different publicly available models that produce detailed forecasts of a storm’s likely effects on sandy beaches along the Atlantic and Gulf coasts. These models and their forecasts can help emergency managers make critical decisions before a major storm strikes, including which areas to evacuate, which roads to use and where to position storm cleanup equipment.

The first model, called the USGS Coastal Change Hazard Forecast, is used to predict the probability and locations protective sand dunes are likely to be eroded at their bases, overtopped by storm waves or inundated by seawater. The model uses observations of beach topography and National Hurricane Center-modeled surge and waves. The USGS coastal hazards storm team works with the NHC to update the USGS coastal change forecasts several times a day. The forecasts typically begin 72 hours before a storm is expected to make landfall. Coastal change forecasts are available at the USGS Coastal Change Hazards Portal. 

A newer model developed by USGS scientists in collaboration with NOAA is called the Total Water Level and Coastal Change Forecast. This model estimates the location and timing of potential coastal impacts as well as the height of stormwater levels at the shoreline, and where protective coastal sand dunes are likely to be eroded at their bases or overtopped by storm waves. This continuously operating model produces six-day forecasts of hourly water levels for almost 3,000 miles of coastline extending from Texas to Maine. These forecasts, which focus on specific sites within several regional stretches of coastline, are available online via the Total Water Level and Coastal Change Forecast Viewer.

For more information on USGS coastal change forecasts, check out this USGS geonarrative.

Total Water Level Forecast for Madeira Beach, FL pre Hurricane Irma — Animation displaying the Total Water Level and Coastal Change Forecast for Madeira Beach, Florida, prior to Hurricane Irma making landfall in September 2017. While Hurricane Irma impacted much of the Southeast, the map in this animation only displays the forecast for the stretch of coastline between Beacon Square and Bonita Springs, Florida.

Come back next week to learn how flooding caused by hurricanes and tropical storms can threaten coastal and inland communities, and how real-time USGS water monitoring information is used to forecast floods and protect communities.

*Editor's note: The photo at the top of the story was taken August 30, 2011, and shows coastal change and damage near Rodanthe, North Carolina, three days after Hurricane Irene made landfall. Photo by Karen Morgan, USGS.