U.S. Department of the Interior
U.S. Geological Survey
AMOUNTS AND RATES OF BLUFF-TOP
RECESSION
ALONG THE LAKE MICHIGAN SHORELINE
AT FORT SHERIDAN, ILLINOIS,
FROM 1872-1987
By Randall W. Jibson
Open-File Report 03-231
U.S. Geological Survey
Golden, Colorado
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial Standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names if for descriptive purposes only and does not imply endorsement by the U.S. Government.
Introduction
This brief report is being released as a result of a public request for data regarding amounts and rates of bluff-top recession at Fort Sheridan, Illinois, which is located along the Lake Michigan shoreline. Previously published reports (Jibson and Staude, 1992; Jibson and others, 1994) contained graphical representations of bluff-recession data along the Lake Michigan shoreline from Wilmette to Waukegan, Illinois; this report contains a table of the numerical data for the Fort Sheridan segment of the previous study area.
Measuring Bluff Recession and Calculating Recession Rates
As described in previously published reports (Jibson and Staude, 1992; Jibson and others, 1994), the 30 km of bluffs along the Illinois shoreline of Lake Michigan from the north side of Wilmette harbor to the north side of the Great Lakes Naval Training Center were divided into 300 segments, each 100 m long. Segments were defined by projecting perpendicular lines from a baseline bearing N. 20° W. and were numbered from south to north. We documented bluff retreat by comparing bluff positions on historical maps and airphotos of different ages. We compared bluff positions from three data sources: 1:20,000‑scale topographic maps made in 1872 by the U.S. Army Corps of Engineers, 1:14,400‑scale airphotos taken in 1936, and 1:14,400‑scale airphotos taken in 1987. On each data source, we measured the distance from the upper edge of the bluff to the Chicago and Northwestern railroad grade, which roughly parallels the shoreline in the area. On the 1872 maps, we plotted the baseline, segmented the bluff, and measured the distance perpendicular to the baseline from the upper bluff edge to the center of the railroad grade at the midpoint of each segment. On the airphotos, we used a zoom‑transfer scope to trace the position of the bluff edge onto U.S. Geological Survey topographic base maps (Evanston, Highland Park, and Waukegan 7½' quadrangles) enlarged to 1:12,000 scale. We plotted the baseline and bluff segments on the maps and measured the distance to the railroad grade for each segment. We measured amounts of recession for the 115‑yr period from 1872 to 1987 and the 50‑yr period from 1937 to 1987. Average annual recession rates were calculated by dividing the total recession for a given time period by the length of that time period.
Primary sources of location error include inherent airphoto distortion and imperfect registration of the map and airphoto on the zoom‑transfer scope. Based on the scale and resolution of the airphotos and on measured registration inconsistencies on the zoom‑transfer scope, we estimate that the combined location error from all sources for single features plotted from airphotos does not exceed 3 m; thus, distances measured between any two features are accurate to within 6 m, and comparisons of two such distances are accurate to within 12 m. Measurements directly from the 1872 maps are estimated to be accurate to within 5 m; comparisons with measurements from airphotos are thus accurate to within 11 m. If location errors are random, they should have little net effect on regional averages calculated from the large data base.
Bluff Recession at Fort Sheridan
Figure 1 shows the segmentation of the bluffs at Fort Sheridan, Illinois. Fort Sheridan includes segments 166-193 of the original segmentation scheme described above and published previously (Jibson and Staude, 1992; Jibson and others, 1994). Table 1 contains bluff-recession data for these segments, including the total amount of bluff-top recession (in meters) and average annual recession rates (in meters/year) for 1937-1987 and 1872-1987.
References
Jibson, R.W., and Staude, J.M., 1992, Bluff recession rates along the Lake Michigan shoreline in Illinois: Association of Engineering Geologists Bulletin, v. 29, p. 103-117.
Jibson, R.W., Odum, J.K., and Staude, J.M., 1994, Rates and processes of bluff recession along the Lake Michigan shoreline in Illinois: Journal of Great Lakes Research, v. 20, p. 135-152.
Figure 1.-- Map showing segmentation of bluffs at Fort Sheridan, Illinois. Each bluff segment is 100 m long; numbering scheme is described in the text. Base map is U.S. Geological Survey Highland Park 7.5’ quadrangle (contour interval 5 feet, published scale 1:24,000)
Table 1.-- Amounts of bluff-top recession and recession rates at Fort Sheridan, Illinois.
|
Bluff |
Total bluff-top |
Average annual |
||
|---|---|---|---|---|
|
1937-1987 |
1872-1987 |
1937-1987 |
1872-1987 |
|
|
166 |
19 |
19 |
0.38 |
0.16 |
|
167 |
16 |
19 |
0.32 |
0.16 |
|
168 |
32 |
30 |
0.64 |
0.26 |
|
169 |
0 |
no data |
0.00 |
no data |
|
170 |
0 |
no data |
0.00 |
no data |
|
171 |
17 |
40 |
0.34 |
0.34 |
|
172 |
21 |
41 |
0.42 |
0.35 |
|
173 |
20 |
40 |
0.40 |
0.34 |
|
174 |
0 |
40 |
0.00 |
0.34 |
|
175 |
15 |
25 |
0.30 |
0.22 |
|
176 |
22 |
32 |
0.44 |
0.28 |
|
177 |
20 |
31 |
0.40 |
0.27 |
|
178 |
22 |
41 |
0.44 |
0.35 |
|
179 |
10 |
24 |
0.20 |
0.21 |
|
180 |
13 |
24 |
0.26 |
0.21 |
|
181 |
8 |
22 |
0.16 |
0.19 |
|
182 |
8 |
17 |
0.16 |
0.15 |
|
183 |
9 |
20 |
0.18 |
0.17 |
|
184 |
0 |
4 |
0.00 |
0.03 |
|
185 |
3 |
6 |
0.06 |
0.05 |
|
186 |
12 |
12 |
0.24 |
0.10 |
|
187 |
14 |
no data |
0.28 |
no data |
|
188 |
19 |
no data |
0.38 |
no data |
|
189 |
23 |
23 |
0.46 |
0.20 |
|
190 |
20 |
20 |
0.40 |
0.17 |
|
191 |
22 |
22 |
0.44 |
0.19 |
|
192 |
25 |
31 |
0.50 |
0.27 |
|
193 |
21 |
29 |
0.42 |
0.25 |
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