A Poor Condition Rating No More
The Linwood Pond Dam is an intermediate, high hazard dam with a maximum height of 17.5 feet. Significant woody vegetation, seepage at the toe of the right downstream slope, an inoperable low level outlet gate, and erosion of the embankments were contributors to the dam receiving a poor condition rating. The spillway also did not have sufficient capacity to pass the spillway design flood (SDF) without overtopping the embankments.
Repair & Design Improvements
Our team provided recommendations for repairs to bring the dam into compliance. We assisted the dam’s owner with repairing the low level outlet gate, removing woody vegetation from the embankments, and filling eroded areas on the upstream slope.
Our team also performed an incremental damage assessment, and received approval from the Office of Dam Safety to reduce the SDF from the ½ Probable Maximum Flood to the 500-year storm. A comprehensive hydraulic/hydrologic analysis was performed, and we developed design alternatives to allow the spillway to safely pass the SDF outflow via embankment overtopping protection. We also developed design plans and permit applications which were approved by the Office of Dam Safety, the Northbridge Conservation Commission, and the Army Corps of Engineers.
Design improvements included removal of woody vegetation, stumps, and root systems on and within 20 feet of the embankments. It also included flattening the downstream slope for improved stability and ease of vegetation maintenance, as well as the installation of a vegetated turf reinforcement mat overtopping protection. A new riprap protection on the upstream slope, and the installation of a sand filter blanket and toe drain system were also part of this project.
Tighe & Bond’s scope of services included providing a damage assessment, a hydrology/hydraulics analysis, as well as dam design. This also included permitting, bidding, and construction engineering services.