Lake Forest Dam & Eel Pass
Project Highlights
Location: Bridgeport, CT
Year Completed: 2010
Cost: $2 M
REFERENCE: Ted Rybak, Civil Engineer, III DEP, Inland Water Resources Division
79 Elm Street Hartford, CT 06106-5127 860-424-3883
PRINCIPAL-IN-CHARGE: James Brockman, P.E.
PROJECT MANAGER: John Brochu, P.E.
WATERSHED AREA: 1.42 sq. miles
LAKE AREA: 68 acres
DESCRIPTION: Lake Forest is located at the north end of the City of Bridgeport. The lake is impounded on the south by a 1,590-foot long earthen embankment. The lone outflow from the lake is through the spillway near the center of the dam. Island Brook is the main inflow as well as the outflow of the lake. The project consisted of a complete engineering study to document the current condition of the dam and determine possible repairs to bring the dam up to current DEP requirements. The study entailed a thorough field investigation, aerial topographic survey including aerial photos, ground control and 40 scale mapping with 2’ contours. Also included was a geotechnical evaluation, an environmental assessment conducted by a soil scientist and a complete hydrologic and hydraulic analysis. All findings were documented in a report which outlined the deficiencies in the dam along with alternative repair scenarios and the associated costs. Certified divers were used to perform underwater investigation of inlet structures and assist in obtaining lake topography during the design phase. Divers returned during the construction phase to assist in water control operations. Macchi Engineers completed the study, design of repairs, design of the eel pass, and is currently providing construction administration and inspection services and the preparation of the emergency operation plan.
The Island Brook channel improvements are part of the Lake Forest Dam Repair project. Currently, the outflow from Lake Forest flows through a 35-foot spillway and down an asphalt and grouted riprap channel into Island Brook. The spillway and channel are severely undersized with deteriorated stone masonry training walls and steep eroded slopes. The proposed improvements to the channel include increasing the width of the spillway and outflow channel to accommodate larger storm events, provide new concrete training walls to protect the dam embankment, and to provide riprap erosion protection in the channel directly downstream of the spillway. In addition, the proposed improvements include a 200-foot long eel passage to provide eel access over the spillway into Lake Forest and farther upstream.
The eel passage connects Island Brook to Lake Forest. It is a 200' long by 5' wide natural stone passage located in the low flow area of the spillway channel. Half of the passage is constructed of modified riprap with 2" clear spacing set in 3" of concrete for mature eels to travel. The other half of the passage is for the smaller eels. It is constructed from concrete splashed riprap, where the splashed riprap is washed immediately after placement to expose the 1-1/4" concrete aggregate.
