Rehabilitation of Henion Pond Dam

Henion Pond and the surrounding property are used as a youth summer camp, and the dam crest served as a walking path connecting camp facilities.

Challenge

The most critical deficiency of this Class II-Significant Hazard structure was the dam’s lack of spillway capacity. There were also significant internal erosion problems within the earth embankment near the existing spillway structure which closed the dam crest to vehicle access. On two occasions, subsidence features developed on the dam crest that warranted activation of the Emergency Action Plan (EAP), lake lowering, and emergency repairs to address the problem.

Solution

The areas of subsidence necessitated the design of emergency repairs, including lake lowering and monitoring the safe operating level of the lake. The subsequent major dam rehabilitation included a new primary spillway structure, construction of an auxiliary spillway by armoring the portion of the embankment to the right of the primary spillway, and then raising and leveling the remaining portion of the embankment crest to provide the required one foot of freeboard during the design storm. The rehabilitation design improved the former potholed walking path and created a safe walkable and drivable dam crest.

Benefit

GZA’s dam professionals helped the client prioritize the repairs to address safety and compliance concerns, phasing the work to accommodate the client’s budgetary constraints.

Early phases of this project were completed by Civil Dynamics, Inc. prior to its acquisition by GZA.