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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: [gallery link="none" size="full" ids="19844,19845,19843"] [post_title] => Pleasant Grove Dam Removal [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => pleasant-grove-dam-removal [to_ping] => [pinged] => [post_modified] => 2026-05-22 18:38:06 [post_modified_gmt] => 2026-05-22 18:38:06 [post_content_filtered] => [post_parent] => 0 [guid] => https://princetonhydro.com/?post_type=project&p=19842 [menu_order] => 0 [post_type] => project [post_mime_type] => [comment_count] => 0 [filter] => raw ) [1] => WP_Post Object ( [ID] => 19549 [post_author] => 1 [post_date] => 2026-04-07 18:08:34 [post_date_gmt] => 2026-04-07 18:08:34 [post_content] => Princeton Hydro was contracted by the Warren Hills School Regional School District (WHRSD) to provide a completed dam inspection, dam breach scenario, hydrologic and hydraulic (H&S) modeling, inundation analysis, and hazard classification for the Warren Hills Dam. Located on a tributary of Pohatcong Creek in Washington Township, Warren County, the earthen dam was constructed circa the 1930s and was reconstructed in the 1990s involving spillway repairs. Upon the completion of Princeton Hydro’s careful evaluation of alternative assessments contained in the inspection report, the Warren Hill School District made the decision to seek dam removal. The unsatisfactory condition rating contained in the inspection report, as well as the need for WHRSD to us an adjacent structure for academic activities in Fall 2020, contributed to the decision. Princeton Hydro was then contracted to facilitate the dam decommissioning and throughout the project development, performed the site survey for the identification of hazardous materials; wetland delineation; site investigation; and sediment sampling, analysis, and probing. Princeton Hydro preformed a stream assessment of the channels upstream of the impoundment, and the downstream mill race. Sediment probes were completed throughout the impoundment to determine the depth of unconsolidated material (sediment) and provide a general understanding of the substrate encountered at refusal depth. The proposed channel within the impoundment reflected existing upstream reaches, the anticipated natural channel type, and the assumed pre-dam channel: a boulder dominated cascade, approximately 12 feet wide, up to two-foot max depth, and 10% slope, with occasional/irregular boulder steps. As part of the engineering design, Princeton Hydro also conducted planning, permitting, and construction management and oversight. The completed design involved sediment excavation and onsite storage, as well as stable channel creation. Through an accelerated schedule Princeton Hydro worked to complete the permitting and dam removal before the start of the 2019 school year. [post_title] => Warren Hills Dam Decommissioning [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => warren-hills-dam-decommissioning [to_ping] => [pinged] => [post_modified] => 2026-04-07 18:08:34 [post_modified_gmt] => 2026-04-07 18:08:34 [post_content_filtered] => [post_parent] => 0 [guid] => https://princetonhydro.com/?post_type=project&p=19549 [menu_order] => 0 [post_type] => project [post_mime_type] => [comment_count] => 0 [filter] => raw ) [2] => WP_Post Object ( [ID] => 19065 [post_author] => 1 [post_date] => 2026-01-12 22:06:44 [post_date_gmt] => 2026-01-12 22:06:44 [post_content] => In 2013, American Rivers, CTDEEP Fisheries, and Natural Resources Conservation Service began collaborating on an effort to remove up to five dams as part of a long-term project to restore connectivity to the Moosup River, prized trout-fishing stream in the Town of Plainfield. Princeton Hydro was contracted with RiverLogic Solutions to provide design-build and permitting services. As part of this larger effort, the most downstream barrier, Hale Factory Dam, was removed in 2014. The remnants of the toppled Griswold Rubber Dam (approximately 2 miles upstream) were removed in 2015. The removal of Brunswick Mill Dam #1 (approximately 0.75 miles upstream) was completed in 2017. Princeton Hydro developed a design-build approach for the project in collaboration with RiverLogic Solutions, a contractor highly specialized in the removal of dams. Princeton Hydro prepared design plans and project permitting, as well as supervised construction for the three dams. RiverLogic Solutions provided design and constructability input, and the construction services to remove each dam. Princeton Hydro proposed a low-cost, low-impact approach to the removal of the Hale Factory Dam that involved the full removal of the structure, the re-use of boulders from the dam for random in-channel placement to enhance aquatic habitat, and the passive recovery of the channel. Griswold Rubber Factory Dam Removal involved the demolition and removal of concrete slabs and the creation of a natural gravel/cobble riffle coupled to the existing pools upstream and downstream of the former spillway to provide enhanced fish habitat. In addition to restoring aquatic organism passage, the Brunswick Mill Dam #1 removal, also provided for removal of a large floodplain constriction and a public safety hazard, and stabilization of an eroding bank. While dam removal is becoming a more common mode of restoring rivers, efforts like this – to remove multiple barriers on a single river – are rare. When clustered on a single river, the ecological benefits to restoring aquatic organism passage and enhancing aquatic habitat are substantially magnified. [post_title] => Moosup River Dam Removals [post_excerpt] => [post_status] => publish [comment_status] => closed [ping_status] => closed [post_password] => [post_name] => moosup-river-dam-removals [to_ping] => [pinged] => [post_modified] => 2026-01-12 22:07:09 [post_modified_gmt] => 2026-01-12 22:07:09 [post_content_filtered] => [post_parent] => 0 [guid] => https://princetonhydro.com/?post_type=project&p=19065 [menu_order] => 0 [post_type] => project [post_mime_type] => [comment_count] => 0 [filter] => raw ) [3] => WP_Post Object ( [ID] => 18593 [post_author] => 1 [post_date] => 2025-10-11 13:50:05 [post_date_gmt] => 2025-10-11 13:50:05 [post_content] => Princeton Hydro has partnered with Wildlands Conservancy for over a decade on multiple dam removals in the Lehigh River Valley. Our firm designed and permitted the removal of eight consecutive barriers on Jordan Creek, including three consecutive low-head dams. We also designed and permitted two low-head dams on Little Lehigh Creek. Collectively, these dam removal projects reconnected miles of river, enhanced aquatic habitat, and improved adjacent parkland and recreational fishing in the economically-stressed, urban communities of Allentown, PA. Building upon the successes of the barrier removals on Jordan and Little Lehigh Creeks, Princeton Hydro partnered with the Wildlands Conservancy again in 2018 to remove a combination of four privately and publicly owned dams on Bushkill Creek in Easton, PA. The dam removal projects served as a model for landowners and municipalities regarding the need for future dam removals throughout the Delaware and Lehigh Valley Watersheds. Having been restored to its natural, free-flowing state in Fall 2024, the barrier removals were part a larger, watershed-wide effort to improve aquatic connectivity, fisheries, and benthic macro-invertebrate and wildlife habitats. The projects restored fish passage, reduced nonpoint source pollution, improved water quality, and restored capacity for groundwater recharge, as well as stabilized and restored the stream’s channels and banks. As part of the barrier removal projects, Princeton Hydro:
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:
Princeton Hydro was contracted by the Warren Hills School Regional School District (WHRSD) to provide a completed dam inspection, dam breach scenario, hydrologic and hydraulic (H&S) modeling, inundation analysis, and hazard classification for the Warren Hills Dam. Located on a tributary of Pohatcong Creek in Washington Township, Warren County, the earthen dam was constructed circa the 1930s and was reconstructed in the 1990s involving spillway repairs.
Upon the completion of Princeton Hydro’s careful evaluation of alternative assessments contained in the inspection report, the Warren Hill School District made the decision to seek dam removal. The unsatisfactory condition rating contained in the inspection report, as well as the need for WHRSD to us an adjacent structure for academic activities in Fall 2020, contributed to the decision.
Princeton Hydro was then contracted to facilitate the dam decommissioning and throughout the project development, performed the site survey for the identification of hazardous materials; wetland delineation; site investigation; and sediment sampling, analysis, and probing. Princeton Hydro preformed a stream assessment of the channels upstream of the impoundment, and the downstream mill race. Sediment probes were completed throughout the impoundment to determine the depth of unconsolidated material (sediment) and provide a general understanding of the substrate encountered at refusal depth. The proposed channel within the impoundment reflected existing upstream reaches, the anticipated natural channel type, and the assumed pre-dam channel: a boulder dominated cascade, approximately 12 feet wide, up to two-foot max depth, and 10% slope, with occasional/irregular boulder steps. As part of the engineering design, Princeton Hydro also conducted planning, permitting, and construction management and oversight.
The completed design involved sediment excavation and onsite storage, as well as stable channel creation. Through an accelerated schedule Princeton Hydro worked to complete the permitting and dam removal before the start of the 2019 school year.
In 2013, American Rivers, CTDEEP Fisheries, and Natural Resources Conservation Service began collaborating on an effort to remove up to five dams as part of a long-term project to restore connectivity to the Moosup River, prized trout-fishing stream in the Town of Plainfield. Princeton Hydro was contracted with RiverLogic Solutions to provide design-build and permitting services.
As part of this larger effort, the most downstream barrier, Hale Factory Dam, was removed in 2014. The remnants of the toppled Griswold Rubber Dam (approximately 2 miles upstream) were removed in 2015. The removal of Brunswick Mill Dam #1 (approximately 0.75 miles upstream) was completed in 2017.
Princeton Hydro developed a design-build approach for the project in collaboration with RiverLogic Solutions, a contractor highly specialized in the removal of dams. Princeton Hydro prepared design plans and project permitting, as well as supervised construction for the three dams. RiverLogic Solutions provided design and constructability input, and the construction services to remove each dam.
Princeton Hydro proposed a low-cost, low-impact approach to the removal of the Hale Factory Dam that involved the full removal of the structure, the re-use of boulders from the dam for random in-channel placement to enhance aquatic habitat, and the passive recovery of the channel. Griswold Rubber Factory Dam Removal involved the demolition and removal of concrete slabs and the creation of a natural gravel/cobble riffle coupled to the existing pools upstream and downstream of the former spillway to provide enhanced fish habitat. In addition to restoring aquatic organism passage, the Brunswick Mill Dam #1 removal, also provided for removal of a large floodplain constriction and a public safety hazard, and stabilization of an eroding bank.
While dam removal is becoming a more common mode of restoring rivers, efforts like this – to remove multiple barriers on a single river – are rare. When clustered on a single river, the ecological benefits to restoring aquatic organism passage and enhancing aquatic habitat are substantially magnified.
Princeton Hydro has partnered with Wildlands Conservancy for over a decade on multiple dam removals in the Lehigh River Valley. Our firm designed and permitted the removal of eight consecutive barriers on Jordan Creek, including three consecutive low-head dams. We also designed and permitted two low-head dams on Little Lehigh Creek. Collectively, these dam removal projects reconnected miles of river, enhanced aquatic habitat, and improved adjacent parkland and recreational fishing in the economically-stressed, urban communities of Allentown, PA.
Building upon the successes of the barrier removals on Jordan and Little Lehigh Creeks, Princeton Hydro partnered with the Wildlands Conservancy again in 2018 to remove a combination of four privately and publicly owned dams on Bushkill Creek in Easton, PA. The dam removal projects served as a model for landowners and municipalities regarding the need for future dam removals throughout the Delaware and Lehigh Valley Watersheds.
Having been restored to its natural, free-flowing state in Fall 2024, the barrier removals were part a larger, watershed-wide effort to improve aquatic connectivity, fisheries, and benthic macro-invertebrate and wildlife habitats. The projects restored fish passage, reduced nonpoint source pollution, improved water quality, and restored capacity for groundwater recharge, as well as stabilized and restored the stream’s channels and banks.
As part of the barrier removal projects, Princeton Hydro:
The Ousatonic Fish and Game Protective Association, Inc., in partnership with the Connecticut Department of Energy and Environmental Protection’s Inland Fisheries Division, sought to remove the Papermill Pond Dam on the East Aspetuck River to restore fish habitat formerly exceptional in quality for trout, facilitate fish passage through the site, and improve accessibility and functionality for people to engage in outdoor activities at the site in order to foster deeper stewardship ethic for the watershed.
The Papermill Pond Dam, located in New Milford, is an embankment dam situated on the East Aspetuck River. It is located 2.9 miles upstream of the confluence with the Housatonic River and is the first barrier on the East Aspetuck River. The spillway is concrete capped with masonry core. It has an approximate structural height of 11 feet and length of 75 feet.
The following alternatives were analyzed: 1) no action; 2) fishway bypass channel around dam; 3) technical fishway at dam; 4) dam lowering with fishway at dam; 5) river bypass and off-line pond; and, 6) full removal. Conceptual designs were developed for each alternative. Each alternative was analyzed and rated numerically relative to twelve categories: river morphology, aquatic resources (fisheries, macroinvertebrates, water quality), recreation, historic resources, flooding, relative liability, relative short-term costs, relative long-term costs, availability of funds, and anticipated permitability. Dam removal ranked as the most feasible alternative, but dam repair stood out as the best option for maintaining the existing ease of recreational access. That alternative necessitated dam repair, ongoing maintenance and inspection, both short-term and long-term sediment dredging, and construction of a fish bypass channel. The Association considered the alternatives and decided to pursue full dam removal.
Based on negotiations with CTDEEP that considered impacts to downstream habitats and other applicable regulations, the resulting recommendation was to remove a portion of the impounded sediment prior to passive release of the remaining impounded sediment, regardless of potential contamination. This minimized transitory sediment deposition in downstream habitats, thereby reducing the short-term impacts of the project. Thus, sediment proximal to the dam is proposed to be excavated and permanently deposited in upland areas onsite.
The dam was successfully removed in 2019 under supervision of CTDEEP Fisheries Division and Princeton Hydro.
The Martin Dam was constructed on an active farm in 1961 as part of USDA’s sustainable farms pond construction initiative. Martin Dam’s robust 4,000 cubic yards of placed dam material resulted in the impoundment of only 3.5 acres of surface water. Several years ago, during the removal of a beaver dam that was obstructing the dam outlet, the riser structure was inadvertently destroyed, and a large part of the earthen dam collapsed. Due to the damage, the dam was put under an enforcement action from the Maryland Department of the Environment (MDE) Dam Safety Program. Site investigations showed an outlet culvert in total disrepair and severe erosion of the dam and downstream areas.
Fearing the risk to property and life from a catastrophic dam failure, GreenTrust Alliance, in partnership with Princeton Hydro, were enlisted to design, develop, and enact an emergency dam breach. The earthen dam was approximately 20 feet in height and 490 feet in length, with an impoundment of approximately 3.48 acres. The contributing drainage area was approximately 0.25 square miles (160 acres) of low density residential land use and the primary inflowing channel, Overshot Branch, was intermittent or ephemeral. The assessment and design involved probing within the impoundment, which revealed water depths averaging 4.7 feet, with a maximum of 7.5 feet, and impounded sediment depths averaging 1.0 foot, with a maximum of 3.0 feet.
Princeton Hydro prepared a 35% design plan for the earthen dam removal, and this plan was subsequently approved by MDE Dam Safety with an emergency permit, forgoing the typical months-long design and review process. The dam breach was implemented in late 2018.
After the dam breach, Princeton Hydro completed a hydrologic and hydraulic assessment. Pre- and post-breach conditions were modeled to determine the potential increase in flood elevations to downstream properties. In addition, a dam failure was also modeled to assess the potential risks should the dam have failed. In comparing the pre-and post-breach scenarios, 100-year flood elevations increased between 0.01 and 0.29 feet for approximately 1 mile downstream of the pond. The floodplain valley for this stream was relatively narrow which means any increases in discharge translated to larger increases on peak flood elevations compared to the total width of the floodplain. However, the narrow floodplain also acted a barrier, ensuring that flooding was mostly contained to the area around the stream itself. No additional structures were inundated as a result of the breach.
Princeton Hydro, along with GreenVest and Green Trust Alliance, developed a design that enhanced in-stream habitat of the downstream reach, and allowed for passive wetland conversion and restoration of the former impoundment.
Princeton Hydro was contracted to investigate, analyze, and design the removal of obstructions and restore natural stream function on Darby Creek. With funding from the National Fish and Wildlife Foundation and Pennsylvania Growing Greener program, the objective of the project was to remove remnant bridge piers in Colwyn and Sharon Hill Boroughs, a failed dam in Darby Borough, a mill dam in Landsdowne and Clifton Heights Boroughs, and a dam in Upper Darby Township and Clifton Heights Borough.
The Kent Park Dam was a placed rock structure that spanned Darby Creek within Kent Park within Delaware County. Princeton Hydro prepared hydrologic and hydraulic analyses; assessed fluvial geomorphic characteristics; determined infrastructure impacts; inventoried natural resources, including wetland delineations and invasive species; and assessed impounded sediment. Design plan sets were prepared, public presentations completed, and permit applications submitted to the Pennsylvania Department of Environmental Protection, U.S. Army Corps of Engineers, and the Delaware County Soil Conservation District.
This project included the reconstruction of the stream bank using bioengineered soil lifts; the innovative construction of a riffle over a sanitary sewer line, which protruded above the stream bed; and the creation of a wetland complex within a small spring tributary to Darby Creek, which reduced sediment contributions to the stream.
Princeton Hydro provided construction observation and administration to ensure the implementation met the stakeholders’ expectations and design intent. This project was funded by the PADEP Growing Greener Grant program, the National Fish and Wildlife Foundation, and a NOAA settlement fund from the 2004 Athos I oil spill on the Delaware River.
The Long Pond Dam currently serves as a barrier to migratory fish along Whitford Brook, a tributary to the Mystic River. Whitford Brook has seen significant declines in fish populations, in part due to dams along the river corridor that prevent fish from accessing upstream spawning habitat. Diadromous fish, including Alewife, Blueback Herring, American Shad, American Eel, and Sea Lamprey rely on access to upstream spawning habitat to complete their life cycle. For Long Pond specifically, CT DEEP Fisheries estimated that fish passage restoration could provide an annual run of more than 250,000 alewives. In conjunction with other recent improvements along Whitford Brook, facilitating fish passage at this location would create a 6.6-mile stretch of connected river corridor from the confluence of Whitford Brook with the Mystic River upstream to the top of Lantern Hill Pond.
A nature-like fishway was identified as the targeted means of providing fish passage by Save the Sound as the configuration of the outlet structure and embankment were well suited to that approach (relative to a technical fishway) and because dam removal was not considered a viable option due to the recreational and habitat (spawning) value of the impoundment.
Princeton Hydro’s scope included: evaluation of existing data including past H&H studies and engineering evaluations/inspections of the dam; site investigations including geomorphic assessment and wetland delineation; topographic, utility, and boundary surveys; development of a concept design; H&H analysis; geotechnical investigations; fish passage design; development of an engineering package (plans, technical specifications, construction cost estimate) and applications for regulatory approvals; and finalization of design documents based on regulatory feedback.
The primary challenge presented by this project was that the dam in its existing configuration was not in compliance with CT DEEP dam safety standards and that improvements/modifications to the dam to bring it into compliance were being handled by others. Further, site constraints dictated that installation of a nature-like fishway would require replacement of the dam’s outlet structure, which would increase the scope and complexity of the project beyond that originally envisioned.
While Princeton Hydro’s design of the nature-like fishway is largely complete, construction can not move forward until finalized plans for bringing the dam into compliance are completed by others and integrated with the proposed fish passage design. Princeton Hydro continues to coordinate with Save the Sound and other project partners to assure that future site improvements will work seamlessly with the proposed fish passage improvements.
Princeton Hydro was contracted by American Rivers to design, apply for permits, and provide construction administration services for the removal of the Kehm Run Dam, an earthen embankment, 270-feet long by 22 feet high, with a cast-in-place ogee spillway, about six (6) feet in height. The former impoundment was five (5) acres in size and contained an estimated 40,000 cubic yards of accumulated sediment. Princeton Hydro conducted a bathymetric survey, developed engineering plans, performed hydrologic and hydraulic analysis, applied to PADEP Dam Safety for a Restoration Waiver, and also to the York County Soil Conservation District plan approval. As part of the regulatory activities, Princeton Hydro subcontracted for a bog turtle (Glyptemys muhlenbergii) Phase I assessment, PA Historic and Museum Commission (PHMC) notices, and filed for a PA Fish and Boat Commission (PFBC) water lowering authorization. The dam was breached in 2019, and the project was completed the following year, with follow up site visits in 2021.
The project was challenging due to the quantity of sediment encountered and its fine-grained nature as a colloidal (very small clay particles), with a relatively small stream immediately downstream. As a result of PADEP Dam Safety inspecting the site, expressing their concerns about the quantity of sediment, Princeton Hydro prepared a revised breach design that provided containment of the sediment, while deregulating the dam. As a result, the former lakebed created an opportunity for its use to as a nature-based BMP to address nutrient loading to the Susquehanna River and Chesapeake Bay. The Susquehanna River Basin Commission saw this opportunity and funded a next phase to further enhance the wetlands created to improve sediment capture from the watershed.
This was a challenging project and has been documented by American Rivers in their blog as “Taking the Lemons and Making some Dam Lemonade”. As a project that provided significant lessons in adaptive management and making the most out of a challenging project.
Connecticut Fund for the Environment (FE) and Save the Sound (STS), in partnership with USFWS and CTDEEP Inland Fisheries Division, secured federal funding to remove the Hyde Pond Dam, restoring Whitford Brook, the primary in-flowing stream to the Mystic River estuary, to a natural free-flowing condition. This created unobstructed fish passage from Mystic River up through the project site, and removed a threat to public safety. The existing dam was an earthen embankment with a concrete capped masonry spillway 4.8 feet high that created a 12-acre impoundment. A fishway installed at the dam by CT DEEP to support a regionally-important river herring run and sea-run brook trout fishery was known to be ineffective due to its outlet location, beaver interference, and frequent low flows due to leakage through the dam. The dam removal restored fish passage to 4.1 miles of stream and provide access for alewife, blueback herring, American eel, American shad, and sea-run brook trout.
Princeton Hydro confirmed through impoundment probing and bathymetric survey that the impoundment contained significant quantities of impounded sediments that had become densely vegetated as scrub-shrub vegetation. Sediment management and wetland impacts became driving factors in the project design and regulatory process. Princeton Hydro coordinated with CT DEEP Planning and Standards Division to develop and approve a sediment sampling plan that included multiple samples throughout the site as well as downstream and upstream.
Results indicated some elevated contaminant levels in some areas. Princeton Hydro developed a sediment management plan and construction sequence, informed by the sediment analysis that balanced active sediment management and passive river restoration. The design entailed excavation of a portion of the sediment prone to mobilization that was then replaced, stabilized, and vegetated on-site.
Princeton Hydro coordinated closely with CFE/STS to negotiate with US Army Corps of Engineers and CT DEEP regulatory divisions to minimize impacts to wetland resources as much as practicable, protect downstream water quality, restore river and riparian functions to the site, and stay within grant cost limits. RiverLogic Solutions provided construction services, and Princeton Hydro provided construction supervision to remove the dam within budget and on schedule in 2015. Since removal, the site has undergone a gradual transition in vegetation but remains a vibrant stream-floodplain wetland complex.
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