As an aftermath to the follow-up flooding to Hurricane Irene in August of 2011, CR 621 overtopped and caused approximately 415 feet of gabion armoring to the downstream side of the roadway to fail and destabilize the downstream embankment. After the flood event, the lake was drained and the substructure for the bridge over the raceway was visible along with the primary and secondary spillway structures for the dam.
Pennoni expedited the design and permitting and provided construction documents for the embankment stabilization, overtopping protection and scour protection of CR 621, which is also the Sunset Lake Dam (NJ ID No. 34-1), that failed during the recent storm events. The most important aspects of the project will be to identify feasible, constructible and cost-effective design concepts, provide plans that minimize the time for permit acquisition, minimize the impact to the traveling public, and reduce long term maintenance.
Pennoni formulated a focused, streamlined, and cost-effective proposal that resulted in the construction of a new embankment stabilization system at the downstream side of West Park Drive (CR 621) at Sunset Lake, and pile rehabilitation and installation of scour countermeasures under the recently constructed County Bridge that carries CR 621 over the Raceway. Pennoni worked closely with Cumberland County using a streamlined, aggressive project approach that will resulted in completing plans that allowed for embankment stabilization within six months to obtain FEMA funding.
Sunset Lake Dam has a NJDEP Class I - High Hazard designation and is situated on Cohansey River within City of Bridgeton, Cumberland County. Sunset Lake Dam is an earthen embankment consisting of hard-packed native sand and silt. The embankment is protected by sheet piles on the upstream side and gabion mattresses on the downstream slope. There is a paved public roadway on top of the 40 foot wide dam crest at the spillway. The roadway is known as West Park Drive (CR 621). The dam embankment is approximately 1,150 feet long and is located on CR 621 between Mayor Aitken Drive and North Park Drive. The primary spillway is located at the eastern end of the embankment and consists of nine siphons discharging to nine 6'h x 8'w box culverts. In addition, the primary spillway has two 5'h x 4'w concrete box culverts controlled by low flow outlet sluice gates. The secondary spillway is located near the center of the embankment and consists of a concrete drop box controlled concrete culvert that discharges to a separate stilling basin. The bridge structure is located at the western end of the embankment and is located over the raceway.
Pennoni was previously retained by the Cumberland County to provide engineering services in conjunction with the regular inspection in conformance with NJDEP Dam Safety standards. Pennoni had prepared annual inspection reports on the condition of the dam, Emergency Action Plan and an Operations and Maintenance Manual in fulfillment of the requirements of the New Jersey Department of Environmental Protection.