In partnership with The Nature Conservancy (TNC), EHS Support embarked on a project to remove the Cedar Grove Dam on New Jersey’s Pequest River, a tributary of the Delaware River, representing a significant step forward in restoring a critical waterway obstructed for over a century. The project was made possible through funding from the National Fish and Wildlife Foundation’s Delaware Watershed Conservation Fund, TNC’s private donors, and the New Jersey Corporate Wetlands Restoration Partnership with demolition work completed by West Bay Construction, Inc. The initiative showcased the power of collaborative conservation efforts and emphasized the value of ecosystem restoration for environmental and recreational benefits. Discover how this impactful project unfolded, the challenges it faced, and the key takeaways for future endeavors.
Background
The Pequest River in White Township, Warren County, New Jersey has been listed as “high priority” in the National Oceanic and Atmospheric Administration Restoration Center’s Northeast Region for fish passage due to co-occurrences of multiple priority species. Diadromous fishes within the Delaware River Basin include a variety of species, such as American Shad and river herring as well as Hickory Shad, Striped Bass, American Eel, Sea Lamprey, and Atlantic and Shortnose Sturgeon.
Populations of some of these fish species have been declining since the 1800s due to overfishing, pollution, and dams blocking fish passage. These species, particularly American Shad, considered “the founding fish”, hold high social, economic, and ecological importance within the Delaware River Basin. Approximately 40% of American Shad historical spawning habitat in North America remains blocked by dams and other barriers. In the Delaware River Basin, American Shad and river herring are at historically low abundance despite fishery closures, bycatch caps, and some habitat improvements. For populations to recover, it’s imperative that many of these obsolete and aging dam structures be removed to enable fish passage.
Project Objective
The objective of the project was to remove the Cedar Grove Dam from the Pequest River. The removal of the Cedar Grove Dam is part of a series of planned dam removals aimed at reconnecting these vital waterways and helping fish return to their historical spawning grounds. The removal of the Cedar Grove Dam will help:
- Reconnect habitats for migratory fish species to return to their historical spawning habitats.
- Improve water quality for resident fish and other aquatic species.
- Enhance recreational opportunities for kayaking, paddling, and fishing enthusiasts.
Removal of the Cedar Grove Dam will amplify the positive impacts that the removal of the three downstream dams (work currently in progress) will have on restoring aquatic connectivity and improving water quality for the benefit of Delaware River Basin trust species.
Project Overview & Dam Removal Design
The Cedar Grove Dam was a 4-foot-high, 75-foot-wide rock and masonry structure constructed in the 1800s. It was located on the Pequest River, about 3.3 river miles upstream from its confluence with the Delaware River at Belvidere, New Jersey.
Prior to removal, the dam was in poor condition and partly breached on the river-left side (right side of the photo), which carried most of the streamflow before splitting around the island feature immediately downstream. Depending on flow conditions, some water also flowed over the center portion and around the right side of the dam. While the dam stored water, the resulting pool was minimal and held no infrastructure, nor did it provide water supply to any known entities.
The area behind the dam primarily consisted of hard cobble substrates, and no significant sediment deposition was observed. Therefore, no sediment management plan was needed in the removal design.
Another critical aspect of the design consideration included the elevation difference between the left and right channels around the downstream island. The left channel sat approximately 1.6 feet higher in elevation than the right channel. Historically, this channel did not exist and was presumably formed because of a historical breach on the left side of the dam. After careful evaluation, the project team decided to proceed with dam removal without bifurcation of the left channel. Instead, the river will be allowed to naturally realign and carve its course toward the right channel, as part of the removal design.
Key Challenges
1. Site Access: Steep, forested riverbanks made accessing the Cedar Grove Dam with heavy equipment particularly challenging. To minimize disturbance, the selected access route followed a natural slope downstream that then paralleled the river upstream to the dam. Unfortunately, this route required traversing a small wetland and removal of some trees. The access route was directed around larger trees, and swamp mats were used to minimize soil compression within the wetland.
Takeaways:
- The shortest route isn’t always the best option. In this case, taking the shortest route would have involved substantial cutting and filling along the riverbank to allow a slope safe for heavy equipment access. This would have potentially jeopardized re-stabilization of the riverbank and would have likely added additional layers of permitting complexity to the project and been more costly.
- Plan for a wider than needed access route in design and permitting phases to allow flexibility. An additional 7 ft was included on each side of the proposed access route in the design and permitting. This provided a 28 ft wide swath to selectively place a 14 ft wide access route, which enabled route layout plans to avoid most larger trees.
2. Regulatory Reviews: Extended permit and regulatory reviews delayed the project timeline. While permits were anticipated by March 2024, they weren’t received until late July 2024, pushing the timeline back several months past the target date. This delay occurred despite proactive completion of specialized surveys (e.g., freshwater mussels and Phase IA archeological) to facilitate review of the permit application.
Takeaways:
- Start the permit application process early and proactively complete necessary surveys. Ensure your permit applications are complete and follow up frequently.
- Consider building a time buffer of 4–6 months into the permitting phase to account for unforeseen delays.
3. Species Timing Restrictions: Timing restrictions for aquatic or terrestrial special status species may impact your project schedule, as they may preclude work during substantial periods of the year to minimize potential for disturbance. This project was subject to timing restrictions for tree clearing from April 1 to October 1 for bats, despite no critical habitats or known hibernation or maternity roosting occurrences in the vicinity.
Takeaways:
- Identify both aquatic and terrestrial special status species timing restrictions early in the planning stages.
- Incorporate these constraints into project timelines to minimize disruptions.
- Collect available survey data to inform whether timing restrictions are warranted.
Project Outcomes
This project will yield lasting and wide-ranging ecological benefits for the Pequest River, and ultimately the Delaware River, including increased ecosystem resiliency and restoration of self-sustaining populations of diadromous fish species. It will also enhance water quality, create more and safer recreational opportunities, and has expanded technical capacity for future dam removals in the Delaware River Basin.
Dam removals yield important ecological benefits, increase recreational opportunities, and can reduce public safety risks. These benefits are especially magnified when viewed through the lens of climate change. Dam removals help ensure that fish and wildlife corridors are connected as species are forced to migrate, and they contribute to the restoration of floodplain functionality, which is increasingly important considering frequent and intense storms.
Future dam removal projects can draw inspiration from this approach, building on lessons learned to further advance fish passage and habitat restoration nationwide. For more information on dam removals, reach out to Greg Murphy.
Greg Murphy
Senior Scientist
Service Line Director, Sediment & Risk Assessment
(215) 527-5857
greg.murphy@ehs-support.com
