GEOG 1710: Shoreline Erosion at Mad Island Marsh Preserve
Introduction & Background.
Mad Island Marsh Preserve is a 3,148-acre tract containing the east arm of Mad Island Lake, its associated freshwater and brackish marshes, and surrounding upland prairie and shrub-land habitats.
Fig. 1. Map of Mad Island Marsh Preserve.
The Gulf Intracoastal Water Way (GIWW) is a man-made canal constructed in 1941 by the U.S. Corps of Engineers. The GIWW cuts through the southern portion of the Preserve and is flanked to the south by man-made islands of dredge spoils.
Fig. 2. Gulf Intracoastal Waterway - view to the west from the preserve shoreline.
Considerable wave erosion has occurred, and continues to occur, along the Preserve shorelines bordering the Waterway. Shorelines along the Waterway are eroded by waves generated by barge traffic.
Figure 3. A large barge passing through the GIWW. The barge generates waves
about 2 feet in height. Thousands of barges travel through the GIWW each year.
Figure 4. A road along the preserve shoreline eroded by wave erosion. In one year, several feet of erosion has occurred.
Figure 5. This fence was constructed several feet back from the shore one year before this photo was taken.
Figure 6. Undercutting has caused this block of soil to fall into the GIWW. It has also destroyed the boat ramp.
The erosion is caused by waves cutting a wave-cut notch and causing collapse and cliff formation.
Figure 7. A small cliff collapses over a wave-cut notch.
The resulting cliff edge is easily identified on air photos.
Figure 8. The resulting cliff along the preserve shoreline has an abrupt edge, easily identified from the air.
Figure 9. The cliff edge (between the
green vegetation and white beach - arrowed) is visible on air photos.
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