Establishing Fish Passage on the West Branch DuPage River

By Stephen McCracken

Dam removal can be an effective technique to restore life and function to river systems, but it’s not always an option. Such is the case for the Fawell Dam, on the West Branch of the DuPage River, McDowell Grove Forest Preserve in northern Naperville.

Mapping of West Branch fish species by the DuPage River Salt Creek Workgroup (DRSCW) found that 12 species dropped out of the fish community in the 26 miles of mainstem river upstream of the dam. These species include relatively large fish like the flathead catfish to small species like the banded darter and emerald shiner. However, because the dam protects valuable infrastructure in downtown Naperville from flooding, removal was not a possibility.

The dam was built by the State of Illinois in the late 1960s. It fell into disuse for a decade before being brought back into use by DuPage County Stormwater Management (DC SWM), its current owner, in the late 1990s. It’s an impressive structure consisting of a concrete spillway made up of three large box culverts flanked by a 20-foot-high dike of over 1000 feet in length. Flow through the culverts can be modulated using movable gates on the upstream face of the dam. This allows for temporary inundations of the McDowell Grove Forest Preserve, a purpose the land was originally set aside for, as opposed to flooding in downtown Naperville. The culvert floors have a steep drop-off from their elevated upstream lip, which appears to be where the barrier to fish passage lies.

Image 1.  Fawell Dam spillway observed from downstream (looking north). The three culverts are clearly visible. The rushing water inside the culverts marks the steep gradient floor section. 

After reviewing a number of possible solutions, DC SWM and the DRSCW settled on installing a Kynard Alternating Side-Baffle Fishway (KASBF) through the eastern-most culvert. The metal structure relies on alternating baffles (see image below) to create a series of eddies that, hopefully, will allow even small-bodied fish to navigate the steep gradient change inside the culvert. The is currently under permitting and is scheduled to be installed in the first half of 2025.

Image 2.  A KASBF on the Eel River in Indiana, showing the alternating baffles. The system to be placed at Fawell has custom-designed baffle spacing and angles, as well as a removable section so that Fawell’s upstream floodgates can be periodically closed.  

Two low-head dams (McDowell Forest Preserve Dam and the Warrenville Dam) upstream of Fawell Dam were removed from the West Branch in 2008 and 2011, respectively. Removal was completed by the DC SWM and the Forest Preserve District of DuPage County. Current data suggests that Fawell is the only remaining barrier to fish passage on the main stem of the river.

The Fawell Project is run jointly by DC SWM and the DRSCW. Funding for the project comes from the DRSCW’s Special Conditions Project Fund.