CATEGORY: Water Resources

OWNER: Illinois Department of Natural Resources

PROJECT FIRM: Farnsworth Group, Inc.

OTHER CONSULTANTS: Illinois Capital Development Board, Midwest Engineering Services, Inc., Huff & Huff, Inc., Wang Engineering, Inc., D. Construction Inc.

DESCRIPTION: The DuPage River Spillway is located within Channahon State Park and is part of the Illinois & Michigan (I&M) Canal State Trail. Originally constructed in the early1900s, this dam was built to supply water to the I&M Canal. It formed an impoundment along the DuPage River, with a feeder gate facilitating the flow of water into the canal through a set of wooden sluice gates. The Canal crosses the river through Lock #6 at the north end of the dam and Lock #7 at the southend. In 1996, a storm caused the river to rise, which led to the overtopping of the earthen embankment portion of the dam south of the spillway. The south embankment was breached and the southernmost span of the spillway was damaged. In response, the IDNR obtained an emergency permit to restore the dam. In 1997-98, they rebuilt the south embankment, constructing it with a sheet pile wall and a rubble embankment topped with riprap. The emergency permit stipulated that the IDNR was to bring the dam up to current regulations. Our primary objective was to identify existing deficiencies and propose solutions to achieve compliance with the regulations that were also in line with the IDNR’s interests in enhancing public access and mitigating upstream flooding. This entailed raising portions of both the north embankment and the saddle dam (a side levee). Elevating the crest of the saddle dam also necessitated raising an historically significant bench, constructed by the Civilian Conservation Corps. Another noteworthy and historical feature of the dam, the feeder gate, required attention as it was in a state of disrepair. Throughout the design and regulatory review periods, the feeder gate continued to be damaged by flooding and debris, as well as general wear and tear throughout the 13-year design process. By the time construction began, there was little left of the feeder gate. However, as a result of documentation obtained over the years, Farnsworth Group was able to design a historically accurate reconstruction and reuse the original metal gears and cranks to operate the gate. The stone abutments of the feeder gate were also salvaged. The project also encompassed tasks such as filling a low area in the north embankment, including the installation of a retaining wall on the upstream side to prevent fill from being placed beneath the water level. Additionally, a fourth spillway bay was constructed to extend the weir’s length from 180 to 250 feet and the existing bridge that carries the I&M Canal Trail was extended with the spillway. To enhance sightlines, the projecting sheet piling along the south embankment was trimmed as per IHPA/SHPO’s request. The crest of the saddle dam was raised by 2.3 feet to provide the required freeboard against overtopping, which also involved elevating the historically significant bench.