Pleasant Grove Dam Removal

Princeton Hydro was contracted to provide ecological restoration and engineering design services for a turnkey mitigation project for the NJ Turnpike Authority to compensate for impacts associated with the Garden State Parkway 83 to 100 Improvements Project. The Pleasant Grove Mitigation Site is located just south of I-195, in the headwaters of a tributary to Toms River. This 130+ acre site was historically cleared, ditched, and dammed for intensive cranberry and row crop production.

The project involved the removal of an earthen dam which created a two-pool impoundment, and restoration of 800 linear feet of zero-order stream channel that had been impaired since 1930. Importantly, this was one of the first compensatory mitigation projects in New Jersey that involved the removal of a dam. The project resulted in re-establishment of 70 acres of forested wetland and forested riparian zone through the enhancement of modified agricultural wetlands, and the preservation of an additional 60 acres, for a total of 130 acres of headwater, forested wetlands, and riparian zone, including the preservation of two stands of Atlantic white cedar swamp.

For this ecologically diverse project, Princeton Hydro provided a multifaceted analysis and design approach, weaving together expertise from in-house ecologists, biologists, fluvial geomorphologists, and hydraulic engineers. Princeton Hydro advocated and justified the re-use of abundant onsite large wood for redistribution throughout the former impoundment, re-planting with seed and plugs, and the passive re-formation of a small, bifurcated channel through a stream-wetland complex.

Understanding the overall lack of risk, and incorporating anticipated lateral adjustment of the stream, allowed Princeton Hydro to design and permit a cost-effective, naturally functioning, and ecologically appropriate stream corridor. The implemented design incorporated a much softer touch than typical stream restoration projects, with native vegetation and large woody material playing a primary role in the form and function of the proposed stream restoration through the former impoundment.

Five years of post-construction monitoring demonstrated ecological uplift and restoration success. This project marked the first permitted use of dam removal as direct wetland mitigation in the State of New Jersey.

The photos below depict the project site Before, During and After construction: