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St. Petersburg Coastal and Marine Science Center > Coastal Change Hazards: Hurricanes and Extreme Storms > Hurricane Rita

Coastal Change Hazards: Hurricanes and Extreme Storms

Holly Beach

Hurricane Rita

Pre- and Post-Storm 3D Topography

In a cooperative research program, the USGS, NASA and the U.S. Army Corps of Engineers (USACE) are using airborne laser mapping systems to survey coastal areas before and after hurricanes. For Hurricane Rita, Texas Bureau of Economic Geology has joined the cooperative effort, using their topographic lidar system to monitor parts of the Texas coast. As the aircraft flies along the coast, a laser altimeter (lidar) scans a several hundred meter wide swath of the earth's surface acquiring an estimate of ground elevation approximately every square meter. The elevation data from different flights can be compared to determine the patterns and magnitudes of coastal change (erosion, overwash, etc.) and the loss (or gain) of buildings and infrastructure. Results shown below come from two NASA lidar systems, the Airborne Topographic Mapper (ATM) and the Experimental Advanced Airborne Research Lidar (EAARL).

Presented here are two lidar data sets from Holly Beach, LA (Figure 1). The first data set was acquired using ATM on October 12, 2002 after Hurricane Lili made landfall well to the east (Figure 2A). The second survey, using EAARL, was acquired on September 28, 2005, 4 days after Rita made landfall 40 kilometers (26 miles) west of Holly Beach (Figure 2B). The devastating impacts of Hurricane Rita are immediately evident. All homes and businesses have been destroyed and most of the debris swept away. The only remaining man-made features are some power poles, concrete slabs, the roads, and the town's water tower.

location map
Figure 1: Location map.

Lidar survey data of Holly Beach, Louisiana.
Figure 2: Lidar survey data of Holly Beach, LA. (A) Map view of topography from NASA ATM survey on October 12, 2002. Structures (in green) and the intersection of State Highways 82 and 27 (top-left corner) are clearly visible. The Gulf of Mexico is located along the bottom of the panel, unsurveyed mainland marsh is located along the top of the panel, north of State Highway 27 and a drainage canal. Boxes indicate locations for expanded views of lidar surveys and matching before/after oblique photography (Figures 3-5). (B) Map view of preliminary topography from the NASA EAARL survey on September 28, 2005 after Hurricane Rita. The intersection of Highways 27 and 82 is sill visible in the upper-left, as is the drainage canal north of Highway 27, but all structures have been destroyed. (C) Preliminary elevation change between October 12, 2002 and September 28, 2005. Shades of red indicate areas of erosion and loss of structures, while shades of green indicate deposition. A striking feature is the line of scour between the two seaward-most roads. [larger version]

The lidar surveys have been differenced to show elevation change between the two surveys (Figure 2C). Red shades indicate a decrease in elevation (erosion or loss of a structure), green shades indicate an increase in elevation (accretion), and gray indicates areas of statistically insignificant change. The vertical change data have been draped over the post-Rita topography. Each red square is a destroyed house, the few green areas show where sand, presumably from the beach, was deposited. Unlike the mainland Mississippi destruction during Katrina, there is only sparse debris evident in either the lidar data or the oblique photography (Figures 3-5).

From a scientific perspective there are several interesting patterns that emerge on this mainland coast. We observe a persistent scour feature roughly in the position of the first line of homes, and just seaward of the seaward-most road. We suspect that this feature was produced by the interaction of the roadbed with strong cross-island flows during the storm. While erosion is pervasive along the shore, we do not observe a spatially coherent overwash deposit such as was seen on Dauphin Island during Hurricane Katrina.

 (A) Oblique photograph of Holly Beach taken June 16, 2001 including the intersection of Highways 82 and 27 near the center of the image. (B) Post-Rita oblique photograph acquired on September 28, 2005. (C) Oblique lidar elevation map of the same region acquired on October 12, 2002. (D) Preliminary oblique lidar elevation map of the same region acquired on September 28, 2005. (E) Preliminary change in lidar elevation between October 12, 2002 and September 28, 2005.
Figure 3: Western Holly Beach, LA. (A) Oblique photograph of Holly Beach taken June 16, 2001 including the intersection of Highways 82 and 27 near the center of the image. (B) Post-Rita oblique photograph acquired on September 28, 2005. Note the absence of intact buildings and the development of a shore-parallel scour feature where the first row of houses used to be located. (C) Oblique lidar elevation map of the same region acquired on October 12, 2002. (D) Preliminary oblique lidar elevation map of the same region acquired on September 28, 2005. The apparent corrugated texture of the topography is due to small differences in elevation from one pass of the lidar system (fly-over) to another which is always discernible to one degree or another. Some of it can be explained by measured, but not yet corrected, drift in GPS signals. (E) Preliminary change in lidar elevation between October 12, 2002 and September 28, 2005. Note the slight erosion on the beach, and the pronounced scour feature along the front row of homes. There was only scattered evidence of deposition (green shades) in the surveyed area. The photographs were acquired as part of a cooperative research program between USGS and the University of New Orleans. [larger version]

(A) Oblique photograph of Holly Beach taken June 16, 2001. (B) Post-Rita oblique photograph acquired on September 28, 2005. (C) Oblique lidar elevation map of the same region acquired on October 12, 2002. (D) Preliminary oblique lidar elevation map of the same region acquired on September 28, 2005. (E) Preliminary change in lidar elevation between October 12, 2002 and September 28, 2005.
Figure 4: Central Holly Beach, LA. (A) Oblique photograph of Holly Beach taken June 16, 2001. (B) Post-Rita oblique photograph acquired on September 28, 2005. Note the absence of intact buildings and the development of a shore-parallel scour feature where the first row of houses used to be located. A shore-oblique channel appears to connect the water-filled scour with the Gulf of Mexico. (C) Oblique lidar elevation map of the same region acquired on October 12, 2002. (D) Preliminary oblique lidar elevation map of the same region acquired on September 28, 2005. The apparent corrugated texture of the topography is due to the small difference in elevation from one pass of the lidar system (fly-over) to another which is always discernible to one degree or another. Some of it can be explained by measured, but not yet corrected, drift in GPS signals. (E) Preliminary change in lidar elevation between October 12, 2002 and September 28, 2005. Note the slight erosion on the beach, and the pronounced scour feature along the front row of homes. There was only scattered evidence of deposition (green shades) in the surveyed area. The photographs were acquired as part of a cooperative research program between USGS and the University of New Orleans. [larger version]

(A) Oblique photograph of Holly Beach taken June 16, 2001. (B) Post-Rita oblique photograph acquired on September 28, 2005. (C) Oblique lidar elevation map of the same region acquired on October 12, 2002. (D) Preliminary oblique lidar elevation map of the same region acquired on September 28, 2005. (E) Preliminary change in lidar elevation between October 12, 2002 and September 28, 2005.
Figure 5: Eastern Holly Beach, LA. (A) Oblique photograph of Holly Beach taken June 16, 2001. (B) Post-Rita oblique photograph acquired on September 28, 2005. Note the absence of intact buildings and the development of a shore-parallel scour feature where the first row of houses used to be located. A shore-oblique channel appears to connect the water-filled scour with the Gulf of Mexico. (C) Oblique lidar elevation map of the same region acquired on October 12, 2002. (D) Preliminary oblique lidar elevation map of the same region acquired on September 28, 2005. The apparent corrugated texture of the topography is due to the small difference in elevation from one pass of the lidar system (fly-over) to another which is always discernible to one degree or another. Some of it can be explained by measured, but not yet corrected, drift in GPS signals. (E) Preliminary change in lidar elevation between October 12, 2002 and September 28, 2005. Note the slight erosion on the beach, and the pronounced scour feature along the front row of homes. There was only scattered evidence of deposition (green shades) in the surveyed area. The photographs were acquired as part of a cooperative research program between USGS and the University of New Orleans. [larger version]
Figure 5Figure 5Figure 4Figure 4Figure 3See close-up of this area.See close-up of this area.See close-up of this area.


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Coastal and Nearshore Mapping with Scanning Airborne Laser (Lidar)
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St. Petersburg Coastal and Marine Science Center > Coastal Change Hazards: Hurricanes and Extreme Storms > Hurricane Rita

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