Problems encountered in establishing a historical erosion-rate database for the Illinois coast of Lake Michigan
- Illinois State Geological Survey, Champaign, IL (United States)
Erosion rates for segments of the Lake Michigan coast at Lake County, Illinois were determined from historical maps prepared by the US Lake Survey and aerial photographs collected for the State of Illinois. Shorelines and blufflines were digitized at 1:20,000 scale for 1872--73, 1910--11, 1947, and 1987; these data were registered to 1:24,000-scale USGS digital line graphs. Erosion rates were calculated from temporal changes on shore-normal transects at 50-m spacing. Three major factors were identified pertinent to future digital mapping of historical coastal changes along similar Great Lakes coasts. (1) Ground-control points and points for rubber sheeting must be carefully selected to ensure these points were stable. For example, road intersections had changed position 15 m or more between early and late data sets. (2) Unlike US ocean coasts, the Great Lakes do not have a standard datum for shoreline mapping, and shorelines are commonly shown for the lake level at the time of the survey. Variation in historical, monthly mean lake level (1.9 m max. range for Lake Michigan) can cause significant shoreline differences between data sets. Shoreline translations of tens of meters may be needed to adjust to a common datum. (3) The bluff crest may not always be an ideal reference line for documenting rates of coastal change. Locally and temporally, recession of the bluff crest may be caused by a variety of slope processes that are independent of wave erosion. Along some bluff coasts, the bluff toe, if carefully defined, may be a more appropriate reference for calculating erosion rates strictly due to coastal processes.
- OSTI ID:
- 5776793
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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