Siegel Marsh Dam is located in Greene Township, Erie County, Pennsylvania, within State Game Land 218. Constructed in 1956, the dam creates a 2,200-acre reservoir used primarily for waterfowl management, hunting, and kayaking. The dam is owned and operated by the Pennsylvania Game Commission (PGC) and is classified as B-3 structure due to size, storage capacity, and potential downstream hazards.

Siegel Marsh Dam currently features two concrete spillways that are connected by earthen embankments. The dam originally consisted of a single spillway; however, a second spillway was added in 1972 and the original spillway weir and embankment crest elevations were raised to both increase storage and spillway capacity.  The reservoir was permanently lowered in 2003 after multiple boils and structural deficiencies were identified with the original spillway, raising concerns regarding the safety of the structure. In addition, the dam is unable to safely pass the design storm event without overtopping the embankment. 

AK Hydro is currently providing design services for the rehabilitation of Siegel Marsh Dam in coordination with Gwin, Dobson, and Foreman. To support the rehabilitation of Siegel Marsh Dam, AK Hydro analyzed the watershed hydrology and routed flows through the existing dam and rehabilitation alternatives. AK Hydro also developed the dam breach model and determined the breach inundation limits downstream of the dam. Hydraulic calculations were performed to size a replacement labyrinth spillway, stilling basin, and RCC overtopping protection.  Design alternatives were also developed that considered the reduction in hydraulic capacity caused by backwater from a downstream bridge. Based on evaluations, conveying design flows through a replacement spillway without overtopping the embankment was not determined to be feasible. As such, all rehabilitation alternatives include roller compacted concrete (RCC) embankment overtopping protection to protect the embankment during overtopping. The client determined that a labyrinth spillway with overtopping protection and a new lake drain was the best option for final design.

AK Hydro is responsible for the design and layout of the labyrinth spillway, stilling basin, and the RCC overtopping protection and is overseeing the development of plan views, profiles, cross sections, and detailed drawings to capture the geometric complexities of the dam. A new lake drain system is also being designed to provide Game Commission staff with improved operational control and long-term maintainability. In addition, AK Hydro is providing support to develop technical specifications, water control plans, permitting, and final design reports. AK Hydro will also provide engineering support during construction.