(Above: Kirby Brook pre culvert restoration. Note the “waterfall” that native brook trout and other fish struggle to leap up in low flow conditions. This is more pronounced in summer months when trout seek thermal refuge from the Shepaug River that this dumps into only yards downstream)
Working with Housatonic Valley Association and Steep Rock Preserve in addition to the Township of Washington in Connecticut who owns the culvert, Trout Scapes performed the construction of this culvert “backup” to ensure that aquatic organisms including native brook trout can enter this coldwater spawning tributary and refuge in all flow regimes. To do so, Trout Scapes worked with Trout Unlimited staff engineers on the final design once permitted to create this passage.
Permitting required getting through reviews of listed dragonfly larvae, the Clubtail Dragonfly, that could potentially be found in Kirby Brook which required continuously flowing water through the site, as well as the potential impacts of driving heavy equipment over the invasive knotweed which can displace it to new areas downstream. Once permitted by US Army Corps, CT DEEP and the Township of Washington Inland Wetlands, work was started and completed in August 2024 during low flow conditions.
(Above: the completed restoration. Trout can now move through each small pool and easily enter the culvert to move upstream to spawning habitat or for thermal relief in warm months when the Shepaug River hits the low 70 degrees.)
To accomplish the restoration plan, the channel above the culvert was restored and a boulder crossvein was buried in a riffle that directs flows into the right side (looking downstream) side of the culvert. That ensures in low flows that all water is in a single box of the two boxes to help fish swim upstream. Additionally, on the immediate downstream side of this culvert, Trout Scapes first installed an 8oz. geotextile and then built a straight boulder sill to slightly back up water inside the culvert. A deep pool was created followed by another touching boulder crossvein which was continued two additional times between the culvert exit and the Shepaug River for a total of three pools. There is excellent forest canopy directly over where this stream enters the much larger Shepaug, preventing the numerous bald eagles and osprey from getting easy meals from above. Based on the fish we saw in talons every day flying by, we’d say the eagles and osprey had plenty of river to hunt without this area of what can be heavy concentrations of trout in summer months.
(Below: building a rock sill directly against the culvert bottom on the downstream exit from the concrete culvert using geotextile fabric to ensure water cannot move between the two when done)
(Below: the finished stream channel now links directly to the bottom of the culvert in all flows and can withstand significant flood events including the Shepaug flows in high water. Note the “step” pools which help trout get relief in warm summer months and to easily move upstream to spawn in late fall.
This process is far less costly than the typical culvert replacement with a bottomless culvert or similar and it doesn’t force that road or trail to be closed except for a few minutes here and there as we had boulders dumped over the edge by the township DPW workers. Everyone pulled together to make this a great success including the many volunteers from Housatonic Valley Association who ensured our entering and exiting the big river each morning and evening didn’t put any invasive knotweed so prevalent on some banks into the river only to take hold downstream.