GeoIS-EM Home         Bald Head Island South Beach evolution

Official long term erosion rates

based on data through 1998

based on data through 1992 select Lockwood Folly inlet to Cape Fear

Dynamic Models of BHI short term evolution

South Beach and Cape Fear 1997-2003
Cape Fear 1997-2003
West section of South Beach 1997-2003

Evolution after the nourishment

Lidar 2000, Lidar 2000 + Dec. 2001, Lidar 2000 + May 2002, Lidar 2000 + Sep. 2002, Lidar 2000 + May and Sep. 2002
for 2003 images see the presentation above

Change in bathymetry 2000 - 2001, data are from the FRF web site

Note: the interferometric elevations posted for 2000 are 30-50cm higher than the 2000 LARC data and probably also the 2001 data in stable areas. This is visible in the 2000 bathymtery (especially along the single path of the interferometric data crossing the area mapped by LARC) and in the change map where this path and most of the area mapped by interferometric sonar shows decrease in elevation (erosion).

Input datafor 2000: blue LARC, white interf. sonar, for 2001, already gridded data were used with non-gridded section filled-in by grid interpolated from LARC data. Bathymetry 2000 Bathymetry 2001
Change 2000-2001, red:erosion,blue:deposition Change 2000-2001 along the South Beach based on LARC data only

Comment: The change map shows increase in elevation (0.5-1.5m) along a 50-150m wide strip of the South Beach. Increase in elevation on the Frying Pan shoals has been as much as 2m. Farther off the South beach shore the bathymetry is extremely stable with change in elevations 10-20cm.

Selected preliminary processing and analysis

RTK-GPS Data processing: spatial interpolationwith anisotropy

Bald Head Island shore 1997 - 2000

• a) Bald Head Island LIDAR DEM, nearshore bathymetry from LARC data, channel and mound bathymetry from sonar.
  b) Overlayed South Beach LIDAR surfaces 1997 and 2000. Note the stable shoreline inflex point and the 1997 convex beach shape in the west and concave shape in the east (West is up in this image). DEM is 5m resolution rasterized by s.to.rast.
  c),d),e) profiles from the overlayed surfaces showing how the shape has changed from
  c) concave to convex in the east section d) little change in the central section with inflex point. e) convex to concave in the west section f) highlighted change in profiles

  a) b)

  c) d) e) f)

• Comparison from interpolated 2m resolution surfaces

  a)beach surface and slope in 1997
  b)beach surface and slope in 2000
  c)difference in elevation between 1997 and 2000 (red is loss, blue is gain)
  

  a) b) c)
  

  
  d), e), f) crossections east, center, west

  d) e) f)
  

  
  Volume change 1997-2000, and annual chnages
  

  Total beach area for which the estimates were computed: 36ha, approx. 4.5 km long. Loss is the volume of eroded sand in m3 computed as a sum of cells that had negative change in elevation (elev. change times the cell area). Gain is the same but for positive elevation change. The dz>1m area is the area in ha that has lost more than 1m elevation.

  --------------------------------------------------------------------------------------
  year             5m res            2m res sm                      2m res
           loss  gain dz>1m area   loss  gain dz>1m area  loss  gain dz>1m area m3 m3 ha
  --------------------------------------------------------------------------------------
  98 - 97  160    42  15           125
  98 - 99 
  98 - 00  254    48  20
  97 - 00  376    65  23           370   50   15           384         24
  ---------------------------------------------------------------------------------------
  
  
  
  Bald Head Island shore 2000-2002
  
  
  
  Total beach area for which the estimates were computed: 22 ha, 4.5km long.
  The area is smaller because data do not extend over the beach dune.
  
  --------------------------------------
  date            loss  gain dz>1m area
  --------------------------------------
  dec01-may02     162          7
  -------------------------------------
  
  
  
  Comparison of the erosion pattern before and after nourishment
  
  a) pattern of elevation change 1997 - 2000 derived from LIDAR data (units are m)
  
  b)  pattern of elevation change Dec. 2001 - May. 2002 derived from RTK-GPS
  (interpolation of December data still needs improvement (higher anisotropy scaling)
  as we do not have the "upper beach path" in the RTK GPS data
  c) sampling pattern: dec. is red and may is black
  
  a)
  b)
  c)
  
  97-00 change - west central section
  
  97-00 change - west central section, draped over elevation
  
  97-98-00 second order change
  
  97-98-00 second order change - west central section
  
  00-Sep. 02 change 
  May 02 - Sep. 02   change 
  Dec 01 - Sep. 02   change 
  
  
  
  -->
  
  Selected shoreline data
  
  
  
  Photos
  
  Cape
  Erosion and a house: west section
  
  
  
  This project is supported by Army Research Office and National Research Council
  
   
  
  
  Processed and visualized
  
  
  by GRASS5