CME’s hydraulics unit created a unique analysis model to demonstrate the viability of the site to support and enhance the passage of native fish species through a culvert proposed for re-lining. The analysis of the site and proposed design features assisted in improving conditions for the native trout population, while minimizing the headwater created by the culvert at flood flows.
CME’s hydraulics unit was asked to provide intensive hydrology and hydraulic analysis in support of the structural design to rehabilitate a deteriorated twin 66” ACCMP culvert in the Town of Marlborough. The project site supported a native brook trout population in its existing condition, but had limited value to allow for passage to the upstream section of Lyman Brook. Further, the structural improvements, which proposed to raise the culvert invert, threatened to create an impassable barrier to fish passage. CME, working extensively with the Inland Fisheries Division of the Connecticut Department of Energy and Environmental Protection, was tasked with ensuring that the ability of fish and other aquatic organisms to pass through the culvert was enhanced rather than reduced. This had to be balanced with the interests of property owners and ensuring that headwater from flood flows and other impacts were minimized.
Through coordination with the Fisheries Division, a design was developed which proposed to line the culvert with HDPE slip-in pipe with interior corrugations and provide additional fish passage enhancements, i.e., baffles within the culvert and pools and weirs at the outlet. The Inland Fisheries Division requested quantification of depths and velocities through the culvert and at critical locations relative to baffles and weirs to ensure compatibility with the swimming capabilities of the native brook trout population. CME’s hydraulics unit responded by developing a unique Aquatic Organism Passage (AOP) model and analysis report to quantify flow depths and velocities across the features of the pipe and brook at low flows representing the time of year of likely fish passage through the culverts. This analysis showed that all design features of the rehabilitated culvert are not only compatible with Fisheries interests but improve the site over existing conditions for the native brook trout population.