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rage ' u • - h eav ains ffec isa ai f Lakes by Robb Collett, DNR Hydrologist Lake levels throughout Minnesota tend to rise and fall. Over many years, lake levels may vary several feet. Lakes aze at the mercy of the hydrologic cycle.. Variables in the cycle include precipitation, evaporation, surface runoff into the lake, groundwater exchange, and size and character of the lakes outlet. For the Chisago Lakes Chain and many other lakes across the state, lake levels are a little more complex.. The Chicago Chain of Lakes outlet was at such a high level and had such a limited capacity, for all. practical purposes the Chain of Lakes had no outlet (they were landlocked). Outflow from this system can only occur through evaporation and flow into the groundwater system. This limited outflow, and the limited inflow from the small watershed (typical of most landlocked lakes), maintain a delicate balance during periods of normal precipitation. Like a bathtub with no drain, water levels could and did rise until the rains stopped. In the mid 1980's the faucet was running full, the bathtub was overflowing; Chicago Lakes were flooding. As a result, Chicago County through the establishment of a Lake Improvement District, with support of many lake residents, took on a project to create an outlet for the chain of lakes. The idea was not to create a bathtub drain to be opened and closed but to provide an cutlet at high water levels. The ordinary high water level (OFiVV), considered to be the boundary of the lake, could be compared to a .ring around the bathtub. 'This ring is determined by DNR professionals who survey and find physical evidence such as vegetation, ice ridges, water stains on rocks, and bridges along the shoreline. The surveyed data is compared to historical levels and records to help establish the OHW or the lakes boundary. By the time the outlet (overflow) was constructed in 1986, precipitation had slowed; water levels had dropped.. Until this year, water levels have not been hig enough to flow out of the outlet. This summer's intense thunderstorms. which have repeatedly targeted the Chicago area, have resulted in great volumes. of precipitation and runoff. The delicate balance between inflow and outflow has been swayed. Water levels have continued to rise throughout the summer. The first test of the outlet project came in mid-August when levels reached the outlet and water began flowing out, nine years after the outlet project's completion. The overflow was designed to be like a nature outlet: when the water levels reach the overflow, water flows out. Because water from the whole chain of lakes ultimately outlets through the overflow, it will. take time for the levels to drop. Lake levels have included and will include levels higher than the outlet/ overflow (as the ring around the lake and historical records have shown). Much of the shoreline around the Chicago Lakes is rather flat; a slight increase or decrease in water levels means the size of Lakeshore owners' frontage covered by water changes greatly. Historical records provide proof the levels rise and fall. a great deal, and Lakeshore owners wishing to buffd or expand should not be fooled. The outlet project is designed to provide relief from long-term high water levels. Water levels were nearly two feet higher during 1986. ...~ntinued on page 11 Outlet projects often are very expensive and require extensive excavauon and grading. The Chisago Chain of Lakes Protect was no exception. Besides physical limitations of outlet construction, projects must con- sider Impact for downstream flooding and other environmental impacts.