Oswego Dam Explained

The following information was provided by David Smith, Water Resources Planner at the IDNR, in response to questions about the dam operation during the high water event over Memorial Day weekend. In summary, the dam was fully operational and was functioning as designed during this time. We have been seeing more flooding events on our lakes due to more frequent high-intensity storms.

The Inflatable Gate at Oswego Dam

An Obermeyer (pneumatic) gate system was chosen for Oswego Dam. The 15’ long gate has a steel panel supported by an inflatable air bladder. The elevation of the lake is adjusted and maintained by controlling the pressure in the bladder. When attached to a portable air compressor, the gate can be raised. Lowering the gate is as simple as deflating a tire.   

The gate operator can easily monitor the pressure in the bladder to check if the desired position is being maintained. Obermeyer gates can be set at a number of positions between fully raised and fully lowered. The gates use no high-precision parts or bearings – enhancing the service life and requiring minimal maintenance. 


At Oswego Dam, on or about May 1 each year, the gate is usually closed (inflated and raised) to restore the lake level to its summer elevation.  On or about November 1, the gate can be opened (deflated and lowered) to accommodate the higher base flow during the winter resulting in a 6” lower lake level.

This year, when the gate was raised for the first time since installation of the control box, the operator noticed a slow pressure drop over several days. The contractor was notified, visited the site, and checked for leaks. They found that one of the valves was not seated tightly and made adjustments. The gate has functioned as designed since the adjustments were made in early May, but frequent checks will continue, especially over a variety of water levels and seasons.

The diagram below shows the components of the gate and the open and closed positions of the steel plates.

Dam Diagram

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