So You Want to Stop Bluff Erosion? You'd Better Plan Ahead

Larsen, C.E. and Clark, I.

U.S. Geological Survey, Reston, Virginia 20192

For the past four years, interns at the USGS have been studying "fossil" and actively eroding bluffs along the Calvert Cliffs in Calvert County, Maryland. The original aim of the study was purely academic. It addressed a classic geomorphologic problem of hill slope evolution.   In simple terms we wanted to know how slopes evolved and at what rates. The Calvert Cliffs provided a laboratory where we could measure progressive change in slopes through time due to movement of prominent coastal landforms along the shore. Three types of landforms provided a time framework that would allow us to calculate rates of change in slope development.   These landforms were a cuspate foreland (Cove Point) migrating downdrift along the shore and sealing the toes of actively eroding bluffs as it prograded southward over a period of 1700 years. Another was a prograding spit sequence (Flag Ponds) that has been deposited during post colonial times; ostensibly 400 years. Finally we looked to modern harbor structures to round out the study. In short, progressive updrift filling behind an historic harbor structure gave us a near real-time framework for understanding the rates at which near vertical and actively eroding and receding bluffs evolve. Our field trip today is designed to demonstrate our results. Slope evolution is clearly a two-part process. Our actively eroding bluffs show an ongoing process of undercutting by wave action and subsequent sloughing of the bluff face to supply sediment to the beach. Once the toes of these bluffs are protected, however, the next process takes over at a longer time period. In short, slumping and in some cases rotational landslides are the next process in the sequence. We were rather astounded by the rapidity at which slopes changed from actively eroding 70 to 80 degree faces to angles of repose on the order of 30 to 35 degrees. It became clear that we had developed a tool for predicting rates of change for slopes in easily erodable sediments. We are going to show you our study sites on the field trip and explain our study rationale along the way.

U.S. Department of the Interior, U.S. Geological Survey
URL: http://geology.er.usgs.gov/eespteam/Atlantic/Larsenabs.htm
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Last modified: 15:16:48 Wed 24 Mar 2004
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