A view of the Spring Lake south pool looking from the cross-levee. Once all water, it has recently been drained to improve infrastructure and allow aquatic habitat restoration.
MIKE MILLER

In past columns, I have discussed the annual flood pulse of our Illinois River. In an ideal year, spring rains give way to summer dry spells, and the river backwaters slowly dry out, exposing mudflats just in time for shorebirds to feed during their long migration. As the dry season continues, wet-soil vegetation sprouts from the seedbank in those mudflats, turning them verdant green with new plant growth. Those plants produce seeds that help fuel the fall waterfowl migration. When fall rains reflood the backwaters, ducks and geese gather to reap the benefits. It is a cycle as old as the river itself, and it has made the Illinois River Valley an important migratory corridor.

MIKE MILLER

In our modern world, that ancient rhythm has become far more complicated. The natural pulse of the Illinois River has been drastically altered by modern culture. On Jan. 2, 1900, engineers opened the gates on a newly constructed lock system that effectively reversed the flow of the Chicago River and connected Lake Michigan to the Illinois River. That increased flow changed the flood pulse. By the 1920s, several levee systems had been constructed up and down the Illinois River, separating backwater lakes from the river channel and allowing agriculture to displace seasonally flooded pools. Starting in 1926, improved locks and dams enhanced river transportation by maintaining a stable channel depth, but they also raised river levels and further altered river hydrology. Again, the flood pulse weakened.

Since the turn of the 21st cen-
tury, 25 years of unusual and unpredictable rainfall have caused the Illinois River to hit flood stage during mid-summer. That timing disrupts the natural production of mudflats and moist-soil plants, negatively affecting the migratory patterns of shorebirds and waterfowl alike. The pulse becomes erratic.

In such an altered river landscape, conservation efforts have focused on restoring a somewhat natural pulse to an ailing river system. By using existing levee systems, conducting artificial water drawdowns during the summer months, and allowing these areas to flood again in the fall, managers have brought some consistency back to the flood pulse. Ecological projects such as The Wetlands Initiative’s Sue and Wess Dixon Waterfowl Refuge near Hennepin, USFWS’s Chautauqua National Wildlife Refuge near Havana, and The Nature Conservancy’s Emiquon Preserve near Lewistown have all been designed to strengthen the river’s flood pulse. They are also great places to observe migratory birds because of that revived rhythm.

Spring Lake offers a current, local example of how these managed drawdowns can put that restoration idea into practice.

This year, the Illinois Department of Natural Resources has conducted a drawdown of the south lake at Spring Lake State Fish and Wildlife Area near Manito. The drawdown will allow IDNR to complete much-needed maintenance on the levee system and roadways while also improving migratory bird habitat on both Spring Lake and Spring Lake Bottoms. It has already exposed hundreds of acres of mudflats that should quickly produce moist-soil vegetation. Earlier this year, fishing regulations were adjusted to allow a fish salvage from the south pool, while the north pool of Spring Lake remains at its normal level. By August, this newly emerging habitat should be a good place to observe shorebirds and to see a managed flood pulse taking shape.