landward and deposited into swales that were formerly behind them, filling them.
A small amount of remaining sand was washed under and around the houses
(many houses were on stilts), and further landward onto the streets. Much of the
beach sands seaward of the dunes were eroded and deposited in the nearshore.
Residents of the Sandhill Shores residential community clearly stated that the
dune and swale structure protected their houses and investments from Ike’s wrath.
The 3-m dunes at Sandhill Shores were considerably taller than dunes on most of
Galveston Island, but the residents were especially vocal that the 3-m deep swale
provided the majority of the protection. According to eyewitness reports, the
breached dunes were swept into the swales, and the majority of the wave energy
continued to break upon and rework these areas. Although the surging waters did
sweep further landward and under the houses, there was no erosion in these areas,
but rather accretion via overwash deposits. The residents strongly stated that they
wanted the dune–swale structure restored after Ike.
A primary objective of the Sandhill Shores project was to restore the dune–
swale structure, as closely to its pre-Hurricane Ike state as possible. Residents
wanted both the restored dune and swale volumes to match pre-Ike volumes, along
the entirety of the community’s 1-km-long shoreline. The challenge was finding a
historical reference to help rebuild the dune and swale to the exact former
dimensions, as the residents desired. A novel technique was developed using
LIDAR, GIS, GPS, and surveying to address this challenge (Fig. 6.3).
Within a GIS, virtual cross-shore transects were created that started at the backbeach and stretched landward across the dunes, beyond the swales up to the base of
the houses. These transects were distributed every 50 m alongshore direction.
Several points were then placed on these transects, with particular care taken to mark
the tops of the dune and its base, the depths of the swale and its interior sides.
Once the points along each transect were selected, their horizontal location was
noted in latitude and longitude coordinates. Pre- and post-Ike aerial photography
was utilized, to confirm locations and assist in the process of adding additional
points. In the field, a GPS was used to find these points, and flags were used to mark
the pre-Ike horizontal locations of the dune and swale.
Fig. 6.3 Using a GIS–LIDAR–GPS survey approach to restoration. Hurricane Ike altered the
dune and swale topography at the Sandhill Shores site. Left image shows pre-storm LIDAR
elevation data, clearly indicating the swale and dune locations (black is low elevation, white is
high). Center image is pre-storm aerial imagery, right image is the post-storm image. In all three
geo-referenced images, the outlined blue area denotes the same swale location, for comparison.
Imagery courtesy of the TNRIS
100
R. Feagin
A small amount of remaining sand was washed under and around the houses
(many houses were on stilts), and further landward onto the streets. Much of the
beach sands seaward of the dunes were eroded and deposited in the nearshore.
Residents of the Sandhill Shores residential community clearly stated that the
dune and swale structure protected their houses and investments from Ike’s wrath.
The 3-m dunes at Sandhill Shores were considerably taller than dunes on most of
Galveston Island, but the residents were especially vocal that the 3-m deep swale
provided the majority of the protection. According to eyewitness reports, the
breached dunes were swept into the swales, and the majority of the wave energy
continued to break upon and rework these areas. Although the surging waters did
sweep further landward and under the houses, there was no erosion in these areas,
but rather accretion via overwash deposits. The residents strongly stated that they
wanted the dune–swale structure restored after Ike.
A primary objective of the Sandhill Shores project was to restore the dune–
swale structure, as closely to its pre-Hurricane Ike state as possible. Residents
wanted both the restored dune and swale volumes to match pre-Ike volumes, along
the entirety of the community’s 1-km-long shoreline. The challenge was finding a
historical reference to help rebuild the dune and swale to the exact former
dimensions, as the residents desired. A novel technique was developed using
LIDAR, GIS, GPS, and surveying to address this challenge (Fig. 6.3).
Within a GIS, virtual cross-shore transects were created that started at the backbeach and stretched landward across the dunes, beyond the swales up to the base of
the houses. These transects were distributed every 50 m alongshore direction.
Several points were then placed on these transects, with particular care taken to mark
the tops of the dune and its base, the depths of the swale and its interior sides.
Once the points along each transect were selected, their horizontal location was
noted in latitude and longitude coordinates. Pre- and post-Ike aerial photography
was utilized, to confirm locations and assist in the process of adding additional
points. In the field, a GPS was used to find these points, and flags were used to mark
the pre-Ike horizontal locations of the dune and swale.
Fig. 6.3 Using a GIS–LIDAR–GPS survey approach to restoration. Hurricane Ike altered the
dune and swale topography at the Sandhill Shores site. Left image shows pre-storm LIDAR
elevation data, clearly indicating the swale and dune locations (black is low elevation, white is
high). Center image is pre-storm aerial imagery, right image is the post-storm image. In all three
geo-referenced images, the outlined blue area denotes the same swale location, for comparison.
Imagery courtesy of the TNRIS
100
R. Feagin