Before and After: Coastal Change Caused by Hurricane Michael

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To learn more about USGS’ role providing science to decision makers before, during and after Hurricane Michael, visit the USGS Hurricane Michael page at https://usgs.gov/hurricane-michael.

Before and after photos show Hurricane Michael's devastation along the Florida panhandle.

According to the National Hurricane Center Storm Surge Unit, Mexico Beach was inundated by 14 feet of storm surge while being battered by large waves and extreme winds, causing complete erosion of the dunes and destruction of the pier and many other buildings. The predicted probability of inundation here was only 58 percent, but the probability of overwash was 94 percent. Because water levels were elevated over several tide cycles, the dunes may have eroded before the storm came ashore, exacerbating the impact of the surge and waves to the dunes and infrastructure behind them. (Public domain.)

The USGS Coastal Change Hazards Storm team is working on a detailed assessment of Hurricane Michael’s effects on Florida’s vulnerable shorelines. The team is currently comparing low-altitude, high angle oblique aerial photos taken by the National Oceanic and Atmospheric Administration in 2017 to similar NOAA photos collected a day after Hurricane Michael made landfall. The USGS scientists are analyzing the photos, which document the hurricane’s impact on the coast, to fine-tune coastal change forecasting models.

“High altitude satellite images give us a big picture view of the coastline, and that’s very useful to identify large areas of overwash, but we can’t see the dunes in those images,” said Kara Doran, the Coastal Change Hazards team leader. “These lower-altitude oblique photos give us a clearer view of the beach and dunes. We can see whether the storm surge and waves altered or eliminated that protective barrier, and what happened to the houses and roads behind the dunes.”

These oblique photos are also extremely useful to USGS researchers because the images are normally taken shortly after a storm has passed, capturing the immediate post-storm conditions of the beaches. This allows the Coastal Change Hazards team to compare their pre-storm coastal change forecast to the post-storm aftermath, assess the coastal change forecast’s accuracy and use that data in future coastal change models.  

“So far, our preliminary analysis indicates our coastal change forecasts performed fairly well in terms of predicating what areas would be affected by overwash, or areas where surge overtopped the dunes,” Doran said. “Along the Florida panhandle, our forecast predicted a high likelihood of overwash from St. Andrews State Park to Mexico Beach, and the dunes in those areas do appear to have undergone overwash.”

Before and after photos show Hurricane Michael's devastation along the Florida panhandle.

Storm surge and waves completely eroded and breached a low, narrow spot on Cape San Blas, creating two new inlets and severing the only road access to T.H. Stone Memorial St. Joseph Peninsula State Park.  The predicted probability of inundation here was only 26 percent, but the scale of the predictions is for 1 kilometer sections of coast, and the model likely did not resolve the low, narrow area that breached.(Public domain.)

One area that saw significant coastal change that was not predicted by the Hurricane Michael Coastal Change Forecast was on T.H. Stone Memorial St. Joseph Peninsula State Park. Michael’s rough waves and surge carved a new breach into the peninsula, washing out the road and turning part of the park into an island.

“Our models don’t take into account the duration of elevated water levels, so when the water levels are above normal days before a storm, those dunes are already eroding before they see the peak impacts from a storm,” said Doran. “That’s an area of interest we are looking into for future research.”

The USGS Total Water Level and Coastal Change Forecast Viewer does provide forecasts of the timing, duration, and magnitude of water levels at the coast, but it is not yet available for most of the Gulf of Mexico. The USGS plans to expand the model into the Gulf in 2019.

When a storm is about to strike the U.S. Atlantic or Gulf coast, the team forecasts the likelihood of coastal erosion and other changes, using a computer model that incorporates the National Hurricane Center’s storm surge predictions and National Oceanic and Atmospheric Administration wave forecasts. The USGS model adds information about the beach slope and dune height to predict how high waves and surge will move up the beach. The model forecasts three types of storm impact to the dunes that protect coastal communities: erosion, overwash, and inundation, or flooding that reaches over and behind the dunes.

The U.S. Army Corps of Engineers, in collaboration with the USGS, is planning to conduct a series of data collection flights along the Florida panhandle coast using airborne lidar, a technology that bounces beams of laser light at the ground to produce detailed elevation information about the surface below. Using that information, the USGS researchers can estimate the volume of sand that Hurricane Michael moved off Florida beaches, measure the height and breadth of the remaining dunes, and be ready to forecast the erosion potential of the next storm.

To learn more about the USGS coastal change hazard team's hurricane research at http://coastal.er.usgs.gov/hurricanes/

Before and after photos show Hurricane Michael's devastation along the Florida panhandle.

Entire buildings were swept off their foundations by Hurricane Michael’s destructive storm surge in Mexico Beach. Sand from the beach has covered the roadways, indicating that surge and waves easily overtopped the dunes and seawalls. (Public domain.)

Before and after photos show Hurricane Michael's devastation along the Florida panhandle.

Low-elevation dunes on St. George Island were overtopped by Michael’s storm surge and large waves. Sand was transported from the beach and dunes,  covering the only access road into St. George Island State Park. The predicted probability of overwash for this location was 100%. (Public domain.)

Before and after photos show Hurricane Michael's devastation along the Florida panhandle.

The low dunes at Tyndall Beach were overtopped and eroded by waves and surge, allowing sand to be transported landward into the marsh. The coastal change forecast predicted a 95 percent probability of overwash at this location. (Public domain.)