Designing an Outfall Extension Through a Beach Renourishment for Deal Lake, New Jersey

The New York District Corps of Engineers has embarked on a major, and ongoing effort to renourish the beaches of northern New Jersey as a cost-effective means of controlling shoreline damage. However numerous existing shoreline structures bisect the nourishment project, inhibiting the natural migration and restoration of the beach back to a continuous, straight shoreline. Various strategies have been applied to compensate for these structures including burial, notching, shortening, and even lengthening. One particular structure is uniquely challenging in that not only does it drain an upland lake, but it also is a migratory path for fish. The Deal Lake outfall is the only pathway for herring to return from the sea to spawn in the lake. To develop a solution for this structure that could bypass sediment to maintain a straight shoreline, yet also create and sustain an open migratory path for fish back up the outfall, a Value Engineering study was initiated at the concept level. The study addressed geometric effects of structure shape on sand bypassing, fish swimming and maneuvering capabilities, and public recreation and interest considerations. Various concepts ranged from systems of fish ladders, to fully submerged outfalls with lighting to orient fish, to jetties spurs, and scour inducing groin heads. A preliminary design concept was constituted from the Value Engineering recommendations and extensively tested in a movable bed physical model. Behavior of the outfall system to bypass sediment under wave loadings from various directions was monitored. The ability for the outfall to remain clear of sediment was enhanced using a concept of reflected wave action to promote sediment agitation. A final design was developed which employed a notch to an existing groin, a downstream spur situated just landward of the notch, and a self-scouring outfall pipe issuing from the spur.