Special Sessions
Sponsored by the Geomorphology Specialty Group
Association of American Geographers 103rd Annual Meeting
San Francisco, California, April 17-21.

Hurricanes III: Geomorphic Impacts

Paper Session 4307
Friday, 4/20/07, from 12:00 PM - 1:40 PM

Sponsorship(s):

Geomorphology Specialty Group
Coastal and Marine Specialty Group

Organizer(s):

Harry Williams - University of North Texas

Chair(s):

Harry Williams - University of North Texas

Abstract(s):

• 12:00 PM Author(s):
  *Stuart E. Hamilton - University of West Florida
  Christopher Houser - University of West Florida
  Natahn Mckinney - University of West Florida
  

  Abstract Title: Quantifying volumetric and morphological changes in barrier islands using an automated comparison of event-paired LiDAR datasets.

  
  

  Topographic data are rarely available in the immediate aftermath of coastal storms. Traditional post-storm analyses consist of manual surveys or aerial photography. Traditional rod-and-laser topographic surveys can take many hundreds of hours to complete and lack the required spatial resolution as area increases. Aerial photography has the temporal facet required by researchers but lends itself to a descriptive analysis rather than providing quantifiable results. Lidar data is increasingly available from a number of differing sources as a baselevel dataset for mapping coastal environments. Lidar has the spatial, temporal, and quantifiable qualities that allow for rapid analyses of coastal environments in the immediate aftermath of storms. This paper explores the potential of Lidar datasets and GIS in quantifying volumetric and morphological changes on northwest Florida’s barrier islands before and after Hurricanes Ivan (2004) and Dennis (2005). An automated model operating in a GIS environment was developed that allows for rapid analysis of beach erosion, overwash, breaching, dune erosion, structural damage, and overall volume change on barrier islands. Lidar data from before Hurricane Ivan, after Hurricane Ivan, and after Hurricane Dennis are automatically processed and analyzed using cartographic modeling techniques. Results presented include volumetric calculations of sand loss/gain in the nearshore environment following a storm event, a profile analysis of dune structures, and measurements of washover deposits.

  Keywords: gis, lidar, hurricane, coastal storms, model, impacts, dune structure, washover

  
  
• 12:20 PM Author(s):
  *Klaus J. Meyer-Arendt - University of West FLorida
  Jon Oravetz - University of West Florida
  Chris Houser - University of West Florida
  

  Abstract Title: Geomorphic Impacts of Hurricane Katrina Upon the Mississippi Barrier Islands.

  
  

  The Mississippi barrier islands (Petit Bois, Horn, Ship, and Cat) are undeveloped and mostly within the Gulf Islands National Seashore. Originating via a combination of shoal emergence and westward longshore drift, today they appear to maintain themselves as independent sediment cells. Mid-latitude and tropical cyclonic storms have flattened dunes and re-shaped island morphology over the years, and this has rendered the islands more vulnerable during subsequent storms. This NPS-funded study documented geomorphic impacts of Hurricane Katrina and their effects upon island recovery and vulnerability to future storms. Subaerial morphologic change was documented by analysis of preand post-storm elevation profiles extracted from NOAA LiDAR data. Bathymetric profiles, spaced at 400m intervals and extended out 1 km on both the Gulf and Sound sides, were generated by echo sounder and compared with pre-storm bathymetric data. Subaerial and subaqueous profiles were lined up across the islands, and empirical orthogonal functions (EOF) analysis was used to identify characteristic island profiles. Results from Petit Bois Island indicate significant dune flattening and shoreline erosion. Despite the erosion, the Gulf bathymetry showed little change, but Sound bathymetric profiles revealed both scour and overwash deposition. Where pre-storm dunes were low (western end), storm surge overwash caused extensive scouring as evidenced by bathymetric ‘drop-off’. In areas of higher dunes (center) or forest (east), soundside deposition was more characteristic. For the Mississippi barrier islands, such morphologic change—and associated redistribution of sediment—is considered to be an important control on the rate and variability of dune and island recovery.

  Keywords: Hurricane Katrina, barrier islands, Mississippi, LiDAR

  
  
• 12:40 PM Author(s):
  James Hansom - University of Glasgow
  

  Abstract Title: Impact of extreme storm waves in the British Isles: modelling the processes of cliff-top erosion and deposition.

  
  

  are common and have been increasing over the last 30 years. However, in spite of increasing damage to offshore installations, the impact of such extreme waves on coasts is unknown. We suggest that several types of cliff-top feature, such as individual boulder fields and organised boulder ridges, sitting atop 15-20m high cliffs along the North East Atlantic and Northern North Sea coasts of the British Isles are related to the previously unrecorded impact of extreme waves. We calculate that extreme waves from offshore arrive virtually un-attenuated at some coasts with enough energy to be capable of substantial erosional damage. We propose mechanisms to account for both the removal of rock from the cliff face under extreme wave impact at altitudes well in excess of those normally found and for the subsequent transport of boulders inland. We show major storm activity in the historic past to be responsible for the emplacement of the features but that substantial reworking occurs during modern storms in an important coastal process that has been previously overlooked on such coasts.

  Keywords: Extreme Storms, waves, cliff-top erosion, model, periodicity

  
  
• 1:00 PM Author(s):
  *Harry Williams - University of North Texas
  William Flanagan - University of North Texas
  

  Abstract Title: Stratigraphy, sedimentology and microfossil content of Hurricane Rita storm surge deposits in southwest Louisiana.

  
  

  Hurricane Rita generated a 4 to 5-meter high storm surge along the southwest Louisiana coast. The storm surge and accompanying waves transported sand and mud into woodland and freshwater marsh environments, located immediately landward of sandy beaches. The resulting storm surge deposits are up to 0.5 m thick and extend at least 500 m inland. Analysis of the stratigraphy, sedimentology and microfossil content of the deposits suggests two distinct phases of deposition: a thin blanket of finer sand and mud, characterized by planar beds, locally reworked into ripples, abruptly overlies the woodland and marsh soils. Calcareous tests of foraminiferal species characteristic of shallow, high-salinity marine environments are common in this layer. These findings suggest deposition from suspension in an early stage of storm surge inundation. The finer sand is overlain by 0.3-0.4 m of coarser sand characterized by prominent foreset beds. The surface of this layer is undulating in woodland areas, due to localized scouring around trees and other obstructions. Foraminiferal tests are rare in this deposit. The coarser sand layer has an abrupt termination about 150 m inland, visible on the ground and in air photographs. These findings suggest the sand is a traction load deposit, formed at a later stage of storm surge inundation. The results of this study have implications for paleotempestology research and efforts aimed at differentiating between geological records of tsunamis and hurricanes.

  Keywords: Hurricanes, storm surge, sedimentation, paleotempestology, Foraminifera, Louisiana, tsunamis

  
  
• 1:20 PM Author(s):
  *Mark Kulp - University of New Orleans
  Mike Miner - Univeristy of New Orleans Department of Earth and Environmental Sciences
  Luis Martinez - University of New Orleans Pontchartrain Institute for Environmental Sciences
  Shea Penland - University of New Orleans Department of Earth and Environmental Sciences
  

  Abstract Title: A Lesson in Rapid Geomorphologic Change: The Impact of the 2005 Hurricane Season on Louisiana Barrier Island Systems.

  
  

  Three hurricanes made landfall along southern Louisiana in 2005. Category 1 Cindy made landfall in July, followed by category 3 Katrina in late August and category 3 Rita in late September. These storms caused unprecedented change along Louisiana barrier islands, clearly indicating the susceptibility of the region to tropical cyclones. Maintaining the Louisiana barrier systems is critical to preserving existing salinity gradients of the regional estuaries and providing protection to interior wetlands and communities by diminishing storm surges. In an effort to document the hurricane-induced changes and processes of change, post-storm high-resolution bathymetric surveys of several tidal inlets were compared to surveys acquired in June 2005 before the hurricanes made landfall. Within Little Pass Timbalier inlet widening of more than 1 km occurred with a redistribution of a sediment volume that was two orders of magnitude greater than the suggested annual longshore transport volume at this location. The magnitude and type of geomorphologic changes in barrier islands were additionally documented through a comparison of post-storm imagery with historical imagery. Image analyses indicates that between 1855 and 2005 the averaged rate of shoreline erosion along the Chandeleur Islands was 7 m/yr. Between 2004 and 2005 however, the average shoreline change was 200 m, within a range of 100 and 400 m. These results need to be carefully considered for management of this coastal zone, which is already subject to high rates of annual land loss that stem from limited sediment supply, land surface subsidence, and absolute sea level rise.

  Keywords: hurricanes, geomorphology, louisiana, change analysis, bathymetric change