“In response to concerns raised by residents regarding data presented to the village about the United States Army Corps of Engineers (USACE) Hofmann Dam project, the village board insisted on a review of data by an independent agency.”
Specifically, they will “simulate results from a verified HEC-RAS model at specified cross sections of the Des Plaines River reach for threshold discharges of the 99 percent, 90 percent, 80 percent, 50 percent, 20 percent and 7Q10 exceedance probabilities determined from the flow-duration analysis, both with and without Hofmann Dam.”
I wonder why this wasn’t insisted upon before we got involved and granted easements.
This project was pitched to the village under false assumptions. In 1950, when the present Hofmann Dam was built, it was constructed at the present 605-foot level because the village, Lyons, the Forest Preserve District and Mosquito Abatement District had 15 years of experience when the old 1908 dam was damaged.
The then-village manager, George Opper, and the Village Attorney Guthrie went to Springfield and worked for 18 months to have this present dam built at the higher level specifically because of the problems caused at periods of low flow, typically May-June to autumn.
Now the Corps wants to essentially destroy the dam and reduce the height of the “crest” there from 605 feet down to about 591 to 594 feet at bedrock – that is, 12 to 14 feet lower than at present. I leave it to you to ponder what kind of conditions this will bring – permanently – to Riverside.
The Corps and IDNR presented numbers relating to the frequency that low flows will occur here that were wrong, and that they knew were wrong. We got into this mess under a completely false set of predictions.
Once this dam is notched and prevented from keeping the impoundment of 156 acre-feet water that we have known for more than 60 years with this dam, and for decades before that with the Fox and Hofmann dams, the river will have frequent annual periods where there will be large areas of exposed mud flats along the banks, trapped pools of water to breed mosquitos, etc. And not just in the area where the Corps is working, but far upriver.
The Corps initially told us the impounded water only extended upriver to the railroad bridge or possibly Forest Avenue, but we now know that in fact the impoundment stretches 6.5 miles, all the way to Lake Street, and that the Corps told the IEPA that approximately 50 percent of the surface of the water upstream of the dam all the way to Lake Street would be lost.
Anyone that looked into the controversy over the dam height would have known this. We need the water level kept at 605 feet – minimum. There is no substitute for the dam. If it is gone, we will experience very adverse conditions in periods of low flow. Forever. Seeking to generate new numbers to somehow justify this project based on a scant week or two of readings is foolish beyond comprehension. This project should be stopped immediately before it is too late.