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LAKE ERIE COASTAL EROSION STUDY |
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The Lake Erie shoreline of Ohio is undergoing widespread recession. Over much of this region, recession rates are less than 1 m/yr (3 ft/yr). However, local rates may exceed 2 m/yr (7 ft/yr). Even where rates are slow, the highly developed nature of the coast makes recession a serious property-damage problem.
The Lake Erie Coastal Erosion Study is a cooperative project of the U.S. Geological Survey and the Ohio Division of Geological Survey to identify the factors controlling the temporal and spatial variation in erosion rates along the Ohio shoreline to improve the predictive models of future shoreline recession. Improved measurement of historic shoreline recession and detailed observations of the geologic and physical factors controlling shoreline recession have been identified as critical needs. Geophysical investigations in the lake basin address transport pathways and identify potentially valuable sand and gravel resources which may be utilized in future shoreline-protection activities. A comprehensive digital database will aid in coastal-management decision making.
The most important objective of the study is to improve the decision-making process--not only how to mitigate an erosion problem, but also on whether to mitigate a problem--by providing objective technical information. The study includes the following components:
- Implementation of the Lake Erie Geographic Information System (GIS). Existing data on geologic framework and processes (recession rates, profiles, lithology, dredging records, and nearshore sand accumulations) is being compiled; newly acquired field data will be entered directly into the GIS. In conjunction with Bowling Green State University, a digital base for Lake Erie and adjacent coastal quadrangles is being developed, along with appropriate digital conversion and registration of other datasets (sample, core, jetted hole, and profile locations; recession rates; bluff height; coastal bedrock and surficial lithologies; nearshore and offshore sediment distribution; and location of geophysical sidescan and sub-bottom trackline data) for incorporation into the GIS.
- Development of prototype sand-budget and erosion-process models for the Ohio coast. Data will be evaluated on the volume and texture of sediments provided to the Lake by fluvial sources, the sediment volumes entering the lake through bluff erosion, and the sand volumes and rates of bypassing that occur updrift of major harbor structures for incorporation in the prototype sand budget. Products will include maps illustrating sediment volume and transport direction, tabulated summaries of sediment volumes for individual watersheds and littoral transport cells, and maps illustrating the dominant modes of erosion along the Ohio lakeshore.
- Analysis of 31 repetitive profiles from Ashtabula and Lake Counties to document changes in nearshore sediment distribution and to evaluate the relationship between nearshore down-cutting and recession rates. Digitized historical profile data are being incorporated into the GIS.
- Preliminary mapping of recession lines based on 1990 aerial photography. Analysis of bluff height, lithology, and morphology; shoreline orientation; lake level; beach width, slope, and composition; and other factors is continuing. Products will include a map series illustrating relative recession rates over multiple time intervals; an erosion index map illustrating the ratio of short-term versus long-term recession rates; and maps illustrating areas prone to increased rates of erosion.
- Continued assessment of lateral and temporal changes in nearshore sediment distribution using closely spaced sidescan sonar/shallow seismic grid lines as far inshore as practicable. A map series illustrating nearshore surficial-sediment distribution will be completed based in part on these data.
- Geophysical data acquisition and interpretation. Reconnaissance maps illustrating top of bedrock and top of glacial deposits (including isopachs of both glacial-related and Holocene lacustrine sediments) have been produced. Additional shore-parallel lines in the nearshore zone between Conneaut and Sandusky and between Sandusky and Little Cedar Point will be used to identify additional areas of offshore/nearshore sand accumulation to tie onshore stratigraphy with offshore geophysical data. Products will include a surficial-sediment-distribution map and cross sections and fence diagrams illustrating subsurface stratigraphy.
- Surficial mapping onshore and modification of existing county report coastal cross sections. County cross sections have been digitized and incorporated into the GIS. Products will include coastal cross sections and maps illustrating surficial geology, bluff lithology and stratigraphy, bedrock geology and structure, and depth to bedrock.
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