Physical Changes of the Lakefront
As 2009 draws to a close, the Edgewater Historical Society has focused on the celebration of the 100th anniversary of the 1909 Burnham Plan with an exhibit at the museum and a lecture at the Edgewater Library. Physical Changes of the Lakefront, by Mike Chrzaskowski, Coastal Geologist of the Illinois State Geological Survey (ISGS) was presented at the Library on Saturday, October 24, 2009. This event was part of the ongoing Austin Wyman Lecture Series. EHS President Bob Remer introduced Mike Chrzakowski.
Dr. Chrzaskowski is the senior Coastal Geologist for ISGS and has lived on both the east and west coasts. His BA and Masters in Geology, Oceanography, are from the University of Washington in Seattle and he earned his PhD from the University of Delaware. Now he is here in Chicago on the “third coast.”
Dr. Chrzaskowski told the audience that the shoreline along Edgewater and Rogers Park once looked like the shoreline at Illinois Beach State Park, 60 miles north of Chicago. Our lakeshore today is the result of many man made adjustments. over the past hundred years since the Burnham Plan.
In 1909 Burnham proposed a series of off shore islands to protect the lake shore from erosion. The west shore of Lake Michigan is affected by a number of forces including NE winds that send waves at an angle to the shoreline. The storm generated waves cause sand to move along the shoreline in a southerly direction, the littoral drift.
Since the 1920s the high bluffs along the shore have been eroding supplying sand to the beaches. This erosion is especially visible in Glencoe and Highland Park. In years past, Kenosha and Waukegan lost 80,000 cubic yards of sand each year. But today this has changed.
According to Dr. Chrzaskowski, the movement of sand along the shoreline has slowed down as it is captured by jetties along the way. At Navy Pier, all sand movement is stopped by the construction of Olive Park just north of the pier.
Eroding beaches can be stabilized with rocks, plants and trees. However, this stabilization creates narrower beaches. Because no sand arrives from the North Shore now, the beaches further south lose volume. These diminished sand volumes show the need for coastal planning.
Other projects like the rebuilding of the revetments at Belmont have little effect on the movement of sand. The structures built at North Avenue Beach are at the top of the class in construction design. They include both groins that are perpendicular to the shoreline and a metal breakwater submerged between them that fosters the collection of sand. The lake bottom at Montrose has a reservoir of sand because of the structures built there in the 1930s WPA shoreline project. The shoreline is not in danger of running out of sand.
Among the remedies for coastal erosion is the use of rocks with “T” groins. Also, since the wave action affects the transport of sand any breakwaters either above or below the surface can stop the waves from carrying the sand.
Dr. Chrzaskowski explained that a headland system is a good way to control the shoreline. A headland is a shoreline surrounded on three sides by water and wave action which changes its form and often creates caves and high bluffs. A headland can be mimicked with “T” groins.
Using a “T” groin with sand placed behind the groin allows the waves to modify the shapes of the shore. In Brazil and in Lake Forest, these groins had developed crescent shaped beaches. The wave refraction around a headland creates a natural beach that does not require sand replenishment from the north.
The water levels of Lake Michigan depend on snow melting and rainfall. It can normally fluctuate up to one foot annually. Periods of wet weather lead to high water levels. The record high was in the fall of 1986-87. Dry periods lead to low water levels. The record low was in 1964. Between 1964 and 1987, the lake levels fluctuated six feet.
Another factor in the lake levels is the outlet from Lake Huron at the St. Clair River. A report in 2005 concluded that dredging over the last century made the channel deeper and more water now flows through. Thus there is more erosion. The report says that this dredging caused a 2.6 foot drop in Lakes Michigan and Huron over the last 100 years. When the lake levels are low, harbor entrances are more shallow, which affects shipping.
Among the 40 people who attended the lecture were Mrs. Austin Wyman and her daughter; Frances Hay, past president of the Mitchell Indian American Museum in Evanston, Ernie Constantino of the 48th Ward Aldermanic Office, Sheli Lulkin, President of ASCO, Eleanor Roemer of Friends of the Parks and Paul Boyd and Thom Greene of the Friends of the Parks Last Four Miles Project.
Thanks to Lee McQueen, Tom Murphy and David Gemperle for editing this text.