Project Description

When built in 1967, the Griffin Creek culvert on Route 199 was only slightly perched above the downstream channel. In subsequent years the channel incised, creating a 3.5 ft (1.1 m) drop at the outlet apron. Attempts to retrofit the outlet in the 1970’s with a concrete step pool created marginal improvement in fish passage conditions. Additionally, hydraulic conditions within the long culvert were unsuitable for passage at most flows.

To improve passage at the outlet, concrete weirs were constructed in 2001. Although designed with 1 ft (0.3 m) drops, the upper two weirs were constructed with 0.5 ft (0.15 m) drops, leaving a 2.5 ft (0.8 m) drop at the lower weir. Subsequently, a rock weir was installed further downstream to reduce the drop.

Corner baffles were installed within the lower 177 ft (54 m) of the culvert barrel to improve hydraulic conditions. The upper portions of the culvert barrel contains large boulders that are believed to provide suitable hydraulic conditions for fish passage. Baffle shape is intended to pass debris and sediment along the left side of the culvert while allowing fish to swim upstream along the right. Spaced 14.8 ft (4.5 m) apart, the corner baffles function as roughness elements at higher flows, reducing velocities and increasing water depths. At the 2-year peak flow baffles were designed to reduce average velocities from 10.3 ft/s (3.1 m/s) to 5.3 ft/s (1.6 m/s). At lower flows baffle placement was designed to create pools that dissipate energy and provide resting areas for smaller fish.

Corner baffles were installed and fastened to the culvert using expansion rings that rest between the corrugations. This technique failed to work as desired due to the culvert’s large diameter and lack of roundness. The expansion ring sagged at the top and the baffles failed to fit tightly between corrugations, which allowed a substantial amount of water to flow under each baffle. Baffles were subsequently retrofitted with metal skirts to seal them.