U.S. Geological Survey Open-File Report 2009-1042
National Assessment of Historical Shoreline Change: A Pilot Study of Historical Coastal Bluff Retreat in the Great Lakes, Erie, Pennsylvania
Although the rates are variable, most of the bluffs along the Lake Erie, Pa., coast are in an erosional state. Bluff retreat results in loss of land and damage to private and community properties. Because coastal environments are of critical importance to the tourist industry and residential development, the U.S. Geological Survey (USGS) is conducting a National Assessment of Coastal Change Hazards. One component of this effort, the National Assessment of Shoreline Change, documents changes in shoreline position as a proxy for coastal change (Morton and others, 2004; Morton and Miller, 2005; Hapke and others, 2006). The USGS has also completed an assessment of coastal cliff erosion in California (Hapke and Reid, 2007) as part of the National Assessment project. In the case of this analysis, the coastal change being assessed is the erosion at the upper edge of the coastal bluff, a commonly used indicator of coastal bluff retreat. The bluff top is used instead of the base for several reasons: (1) the base is sometimes obscured by shadowing in our data sources; (2) the bluff base is irregularly interpreted on the historical imagery; and (3) emplacement of seawalls and revetments, some of which may not be identifiable on the light detection and ranging (lidar) data, can result in apparent accretion of a bluff base.
A principal purpose of the USGS coastal change research is to develop repeatable methodologies for measuring change so that the database of change along the coast of the United States can be periodically and systematically updated in an internally consistent manner. The primary objective of this effort is to implement consistent and regionally applicable methods of assessing and monitoring coastal bluff retreat.