State of the Beach/State Reports/AL/Beach Erosion
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Following landfall of Hurricane Ivan on the Alabama coast on September 16, 2004, the Geological Survey of Alabama conducted monitoring/field reconnaissance, cross-shore profile data acquisition, and analysis to generate shoreline rate-of-change maps representative of 1990 to 2004. Local government officials noted that this beach profile rate-of-change information has been useful in making strategic planning, zoning, and land use decisions. Local communities have utilized the data to receive additional credit under the Nation Flood Insurance Community Rating system.
The Coastal Resources Section conducts research within Alabama’s coastal zone to increase our understanding of beach and shoreline change, environmental quality, and land use, and to acquire and develop supporting digital themes and data sets. Coastal assessments provide resource managers and community planners with information critical to balancing sustainable growth and protecting the natural resources of our coastal areas. Recent section activities include Beach Assessments, investigation of Sand Resources, GIS and Remote Sensing, and GIS Support during natural disasters.
The report Historical Changes in the Mississippi-Alabama Barrier-Island Chain and the Roles of Extreme Storms, Sea Level, and Human Activities by Robert A. Morton of the U.S. Geological Survey (2007) discusses natural and human-caused factors influencing erosion of barrier islands off the coasts of Alabama (Dauphin Island) and Mississippi. Following is the summary from that report:
"An historical analysis of images and documents shows that the Mississippi-Alabama (MS-AL) barrier islands are undergoing rapid land loss and translocation. The barrier island chain formed and grew at a time when there was a surplus of sand in the alongshore sediment transport system, a condition that no longer prevails. The islands, except Cat, display alternating wide and narrow segments. Wide segments generally were products of low rates of inlet migration and spit elongation that resulted in well-defined ridges and swales formed by wave refraction along the inlet margins. In contrast, rapid rates of inlet migration and spit elongation under conditions of surplus sand produced low, narrow, straight barrier segments.
Since the mid 1800s, average rates of land loss for all the MS islands accelerated systematically while maintaining consistency from island to island. In contrast, Dauphin Island, off the Alabama coast, gained land during the early 20th century and then began to lose land at rates comparable to those of the MS barriers. There is an inverse relationship between island size and percentage of land reduction for each barrier such that Horn Island lost 24% and Ship Island lost 64% of its area since the mid 1800s. Ship Island is particularly vulnerable to storm-driven land losses because topographic and bathymetric boundary conditions focus wave energy onto the island. The three predominant morphodynamic processes associated with land loss are: (1) unequal lateral transfer of sand related to greater updrift erosion compared to downdrift deposition, (2) barrier narrowing resulting from simultaneous erosion of the Gulf and Sound-side shores, and (3) barrier segmentation related to storm breaching. The western three fourths of Dauphin Island are migrating landward as a result of storms that erode the Gulf shore, overwash the island, and deposit sand in Mississippi Sound. Petit Bois, Horn, and Ship Islands have migrated westward as a result of predominant westward sediment transport by alongshore currents, and Cat Island is being reshaped as it adjusts to post-formation changes in wave and current patterns associated with deposition of the St. Bernard lobe of the Mississippi delta.
The principal causes of barrier island land loss are frequent intense storms, a relative rise in sea level, and a deficit in the sediment budget. The only factor that has a historical trend that coincides with the progressive increase in rates of land loss is the progressive reduction in sand supply associated with nearly simultaneous deepening of channels dredged across the outer bars of the three tidal inlets maintained for deep-draft shipping. Neither rates of relative sea level rise nor storm parameters have long-term historical trends that match the increased rates of land loss since the mid 1800s. The historical rates of relative sea level rise in the northern Gulf of Mexico have been relatively constant and storm frequencies and intensities occur in multidecadal cycles. However, the most recent land loss accelerations are likely related to the increased storm activity since 1995.
Considering the predicted trends for storms and sea level related to global warming, it is clear that the barrier islands will continue to lose land area at a rapid rate without a reversal in trend of at least one of the causal factors. The reduction in sand supply related to disruption of the alongshore sediment transport system is the only factor contributing to land loss that can be managed directly. This can be accomplished by placing dredged material so that the adjacent barrier island shores receive it for island nourishment and rebuilding."
Those conclusions are not shared by the U.S. Army Corps of Engineers, who published a study Channel Dredging and Geomorphic Response at and Adjacent to Mobile Pass, Alabama (September 2010). The abstract from that study states:
"The entrance to Mobile Bay, Alabama, between Mobile Point on the western end of the Morgan Peninsula and Pelican Point on the eastern end of Dauphin Island, is an extensive natural inlet that has been improved by channel dredging activities since 1904, primarily through the outer bar at the seaward extent of the ebb-tidal delta. The purpose of this study was to evaluate the potential impact of construction and maintenance dredging activities for the Federal navigation project in Mobile Outer Bar Channel on ebb-shoal changes and shoreline response along Dauphin Island, Alabama. Ebb-shoal changes and shoreline response relative to storm and normal forces, and dredging in the outer bar channel, were evaluated to determine the extent to which beach erosion along Dauphin Island could be attributed to U.S. Army Corps of Engineers (USACE) channel construction and maintenance dredging operations.
Two distinct periods were evaluated: one representing conditions prior to significant construction and maintenance dredging activities to determine natural changes (1847/48 to 1917/20), and the other representing conditions after significant changes to the outer bar channel had been imposed (1917/20 to 1986/2002) to quantify changes on the ebb shoal and beach response along Dauphin Island. Overall, net sediment transport from east-to-west for the entire period of record has been supplying sand quantities necessary to produce net deposition on the islands and shoals of the ebb-tidal delta, infill and nourish storm breaches and washover surge channels on Dauphin Island, and promote growth of the western end of the island, even though channel dredging has been active. Based on all available information, there appears to be no measurable negative impacts to ebb-tidal shoals or Dauphin Island beaches associated with historical channel dredging across the Mobile Pass Outer Bar."
- "In Alabama, coastal land loss is caused primarily by beach and bluff erosion. Other mechanisms for loss, such as submergence, appear to be minor. Slope failure accounts for much of the land loss along the east and west shores of Mobile Bay (Smith, 1990). Although bay shorelines were not analyzed in this study, Smith (1990) reported that high bluffs on the eastern side of the bay are retreating at rates of -1 to -1.5 m/yr. Along the Alabama Gulf shoreline, the western half of Dauphin Island is experiencing short-term erosion of as much as -4.7 m/yr. An exception is the westernmost 3 km of the island, which is accreting as the island lengthens to the west. Stumps of former pine trees exposed on the beach at the Dauphin Island Public Beach are evidence of long-term beach erosion. Just east of the park is a large, active dune complex that is migrating into the pine forest and burying the trees. Although the reason for this dune migration is unclear, it is likely that this dune sand would reduce beach erosion to the west if it were available to the littoral system. Elsewhere along the Alabama Gulf shore, Morgan Peninsula and Perdido Key are relatively stable owing to a sufficient supply of sand by longshore transport to the west and local beach nourishment."
"State-of-the-beaches" of Alabama: 1998 by Scott L. Douglass, Bradley Pickel, and Brian Greathouse, Civil Engineering Department, University of South Alabama "was written for citizens interested in the scientific understanding of Alabama's Gulf beach erosion that has been developed over the past few years through research at the University of South Alabama. The report attempts to explain the analysis tools and results in a format for laymen. Some suggestions for future management decisions also are included at the end of the report." The report shows Alabama Gulf Coast shoreline trends from 1970 to 1997 and discusses the impact of Hurricane Georges in 1998.
The Heinz Center's Evaluation of Erosion Hazards, conducted for the Federal Emergency Management Agency (FEMA), studied the causes of coastal erosion hazards and proposed a variety of national and regional responses. The study, published in April 2000, concentrates on the economic impacts of erosion response policies as well as the cost of erosion itself to homeowners, businesses, and governmental entities.
A NOAA website that has graphs of sea level data for many coastal locations around the country over the last 40 to 50 years and projections into the future is Sea Levels Online.
NOAA Shoreline Website is a comprehensive guide to national shoreline data and terms and is the first site to allow vector shoreline data from NOAA and other federal agencies to be conveniently accessed and compared in one place. Supporting context is also included via frequently asked questions, common uses of shoreline data, shoreline terms, and references. Many NOAA branches and offices have a stake in developing shoreline data, but this is the first-ever NOAA Website to provide access to all NOAA shorelines, plus data from other federal agencies. The site is a culmination of efforts of NOAA and several offices within NOS (including NOAA’s Coastal Services Center, National Geodetic Survey, Office of Coast Survey, Special Projects Office, and Office of Ocean and Coastal Resource Management) and other federal agencies to provide coastal resource managers with accurate and useful shoreline data.
A related site launched in 2008 is NOAA Coastal Services Center's Digital Coast, which can be used to address timely coastal issues, including land use, coastal conservation, hazards, marine spatial planning, and climate change. One of the goals behind the creation of the Digital Coast was to unify groups that might not otherwise work together. This partnership network is building not only a website, but also a strong collaboration of coastal professionals intent on addressing coastal resource management needs. Website content is provided by numerous organizations, but all must meet the site’s quality and applicability standards. More recently, NOAA Coastal Services Center has developed a Sea Level Rise and Coastal Flooding Impacts Viewer as part of its Digital Coast website. Being able to visualize potential impacts from sea level rise is a powerful teaching and planning tool, and the Sea Level Rise Viewer brings this capability to coastal communities. A slider bar is used to show how various levels of sea level rise will impact coastal communities. Completed areas include Mississippi, Alabama, Texas, Florida, and Georgia, with additional coastal counties to be added in the near future. Visuals and the accompanying data and information cover sea level rise inundation, uncertainty, flood frequency, marsh impacts, and socioeconomics.
Erosion Contact Info
Hazard Avoidance Policies/Erosion Response
See the Erosion Response section.
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