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A recent return visit confirms what restoration practitioners know well: when barriers are removed, rivers heal. Today, the Paulins Kill flows freely through the former Paulina Lake Dam site, reconnecting habitats that had been fragmented for generations. The Paulina Lake Dam stood for nearly 130 years in Blairstown Township, Warren County, NJ. Constructed in the late 1800s to generate hydropower, it had long outlived its original purpose. Like many aging dams across the country, it remained in place despite no longer serving a critical function, while continuing to disrupt river processes and pose growing safety risks. [caption id="attachment_19094" align="aligncenter" width="800"] Paulina Lake Dam aerial view prior to removal. Photo by Jim Wright/TNC/LightHawk[/caption] As reported in CentralJersey.com’s recent feature “The fall of dams and rise of rivers,” the majority of New Jersey’s approximately 1,700 regulated dams were built in the 19th and early 20th centuries to power mills that no longer exist. Fewer than a dozen still serve an essential purpose today. Many persist due to nostalgia, misunderstanding, or uncertainty around removal—despite blocking fish passage, trapping sediment, warming water temperatures, exacerbating flooding, and increasing the risk of failure. The removal of Paulina Lake Dam was led by The Nature Conservancy (TNC) in partnership with Blairstown Township, New Jersey Department of Environmental Protection, U.S. Fish and Wildlife Service, Riverlogic–Renova Joint Venture, and Princeton Hydro. The Office of Natural Resources Revenue awarded a grant to TNC to fund a substantial portion of the removal through the Paulins Kill and Pequest Watershed Natural Resource Restoration Grant Program. The project advanced through carefully sequenced phases, beginning with controlled notching in late 2023, followed by full demolition and sediment management in 2024, and transitioning into final adaptive management and habitat enhancement in 2025. What the River is Showing Us Now The ecological response has been swift and visible. With the dam removed, more than 7.6 miles of mainstem and tributary habitat have been reconnected at the Paulina Lake site alone. The removal of the Paulina Lake Dam represents one important element of a longer-term, watershed-scale restoration initiative launched in 2013 to restore connectivity and ecological function along the Paulins Kill River. As the downstream most dam on the river, its removal builds upon earlier restoration milestones achieved through the removal of four dams: the Columbia Lake Main and Remnant Dams in 2019, the County Line Dam in 2021, and now the Paulina Lake Dam, progressively reconnecting approximately 45 miles of mainstem and tributary habitat. Since 2016, The Nature Conservancy has also implemented a 10-year Measures and Monitoring Program to track ecological response and conservation outcomes, providing clear evidence that coordinated, science-based restoration can support a healthier, more resilient river system. The river channel is actively stabilizing, riffle and run sequences are re-forming, and previously inundated areas are beginning to revegetate. Cooler water temperatures and the restoration of sediment transport processes are enabling the Paulins Kill to function more consistently with a cold, free‑flowing, coarse‑substrate stream system. This series of aerial drone photos was captured during a site visit in November 2025: [gallery link="none" size="medium" ids="19109,19110,19111"] This recovery is already benefiting aquatic life. As Beth Styler Barry, Director of Freshwater Programs for The Nature Conservancy in New Jersey, noted in the CentralJersey.com article, “We’re already seeing American shad above the dams that were removed. We’re seeing sea lamprey and American eel. It used to be that only the biggest eels could make it upstream. Now we’re seeing all age classes.” By reconnecting upstream and downstream populations that had been isolated for generations, the project has also restored connectivity for rare freshwater mussels, including the endangered dwarf wedgemussel (Alasmidonta heterodon) and triangle floater (Alasmidonta undulata). “All of the organisms in a river like the Paulins Kill evolved to live in a cool, flowing, rocky-bottom stream,” Styler Barry told CentralJersey.com. “When you restore flow, the river begins to heal itself.” Watch the Project from Start to Finish A newly released project video captures this transformation in a way that still images and written updates cannot. Drawing on aerial footage collected by The Nature Conservancy’s Volunteer Drone Team prior to demolition and by Princeton Hydro throughout and after construction, the video documents the full arc of the Paulina Lake Dam removal from initial notching through full demolition and into the restored conditions visible today. The footage provides a comprehensive look at dam removal in practice, illustrating how careful sequencing, sediment management, and adaptive design allow rivers to recover rapidly once barriers are removed. Click below to watch the full project video and see the transformation unfold: [embed]https://www.youtube.com/watch?v=T6dQRRU5DCE[/embed] Beyond ecological gains, the removal of Paulina Lake Dam has significantly improved public safety and community resilience. In CentralJersey.com, Geoffrey M. Goll, PE, President of Princeton Hydro, emphasized the long-term risks associated with aging dams. “If you don’t take care of them, they’ll come out on their own—and that’s a much bigger problem. Once dams are properly removed, people start to see the value of a free-flowing river.” Many dams were never designed to withstand today’s hydrologic conditions. With climate change driving more frequent and intense rainfall events, proactive removal reduces flood risk, eliminates inspection and maintenance liabilities, and allows rivers to function as more resilient, self-sustaining systems. At the Paulina Lake site, removal has also improved recreational access and restored a more natural landscape for the community. Looking Ahead While the Paulins Kill now flows freely through the former Paulina Lake Dam site, final project phases focus on adaptive management, targeted bank stabilization, habitat feature enhancement, and native tree planting to support long term ecological resilience. As the river continues to adjust and evolve, the Paulina Lake Dam site stands as a clear example of what is possible when outdated infrastructure is thoughtfully removed and natural systems are given the opportunity to recover. To learn more about TNC's work to restore the Paulins Kill River, click here. To learn more about Princeton Hydro's work to remove dams and restore rivers throughout the Northeast, click here. [post_title] => Then and Now: Paulina Lake Dam Removal [post_excerpt] => [post_status] => publish [comment_status] => open [ping_status] => open [post_password] => [post_name] => then-and-now-paulina-lake-dam-removal [to_ping] => [pinged] => [post_modified] => 2026-01-28 15:59:36 [post_modified_gmt] => 2026-01-28 15:59:36 [post_content_filtered] => [post_parent] => 0 [guid] => https://princetonhydro.com/?p=19057 [menu_order] => 0 [post_type] => post [post_mime_type] => [comment_count] => 0 [filter] => raw ) [1] => WP_Post Object ( [ID] => 14684 [post_author] => 1 [post_date] => 2024-04-10 15:23:17 [post_date_gmt] => 2024-04-10 15:23:17 [post_content] => Nestled within the New Jersey townships of Hamilton, Robbinsville, and West Windsor lies Miry Run Dam Site 21—an expansive 279-acre parcel with a rich history dating back to its acquisition by Mercer County in the late 1970s. Originally earmarked for flood mitigation and recreation, this hidden gem is on the cusp of a remarkable transformation, poised to unveil its true potential as a thriving public park. Central to the revitalization efforts is a comprehensive Master Plan, meticulously crafted by Mercer County Park Commission in partnership with Simone Collins Landscape Architecture and Princeton Hydro. This visionary roadmap encompasses a spectrum of engineering and ecological uplift initiatives, including:
More than a century after the Paulina Lake Dam first altered the Paulins Kill River, the site now tells a very different story. A recent return visit confirms what restoration practitioners know well: when barriers are removed, rivers heal. Today, the Paulins Kill flows freely through the former Paulina Lake Dam site, reconnecting habitats that had been fragmented for generations.
The Paulina Lake Dam stood for nearly 130 years in Blairstown Township, Warren County, NJ. Constructed in the late 1800s to generate hydropower, it had long outlived its original purpose. Like many aging dams across the country, it remained in place despite no longer serving a critical function, while continuing to disrupt river processes and pose growing safety risks.
As reported in CentralJersey.com’s recent feature “The fall of dams and rise of rivers,” the majority of New Jersey’s approximately 1,700 regulated dams were built in the 19th and early 20th centuries to power mills that no longer exist. Fewer than a dozen still serve an essential purpose today. Many persist due to nostalgia, misunderstanding, or uncertainty around removal—despite blocking fish passage, trapping sediment, warming water temperatures, exacerbating flooding, and increasing the risk of failure.
The removal of Paulina Lake Dam was led by The Nature Conservancy (TNC) in partnership with Blairstown Township, New Jersey Department of Environmental Protection, U.S. Fish and Wildlife Service, Riverlogic–Renova Joint Venture, and Princeton Hydro. The Office of Natural Resources Revenue awarded a grant to TNC to fund a substantial portion of the removal through the Paulins Kill and Pequest Watershed Natural Resource Restoration Grant Program.
The project advanced through carefully sequenced phases, beginning with controlled notching in late 2023, followed by full demolition and sediment management in 2024, and transitioning into final adaptive management and habitat enhancement in 2025.
The ecological response has been swift and visible.
With the dam removed, more than 7.6 miles of mainstem and tributary habitat have been reconnected at the Paulina Lake site alone. The removal of the Paulina Lake Dam represents one important element of a longer-term, watershed-scale restoration initiative launched in 2013 to restore connectivity and ecological function along the Paulins Kill River. As the downstream most dam on the river, its removal builds upon earlier restoration milestones achieved through the removal of four dams: the Columbia Lake Main and Remnant Dams in 2019, the County Line Dam in 2021, and now the Paulina Lake Dam, progressively reconnecting approximately 45 miles of mainstem and tributary habitat.
Since 2016, The Nature Conservancy has also implemented a 10-year Measures and Monitoring Program to track ecological response and conservation outcomes, providing clear evidence that coordinated, science-based restoration can support a healthier, more resilient river system.
The river channel is actively stabilizing, riffle and run sequences are re-forming, and previously inundated areas are beginning to revegetate. Cooler water temperatures and the restoration of sediment transport processes are enabling the Paulins Kill to function more consistently with a cold, free‑flowing, coarse‑substrate stream system.
This recovery is already benefiting aquatic life. As Beth Styler Barry, Director of Freshwater Programs for The Nature Conservancy in New Jersey, noted in the CentralJersey.com article, “We’re already seeing American shad above the dams that were removed. We’re seeing sea lamprey and American eel. It used to be that only the biggest eels could make it upstream. Now we’re seeing all age classes.”
By reconnecting upstream and downstream populations that had been isolated for generations, the project has also restored connectivity for rare freshwater mussels, including the endangered dwarf wedgemussel (Alasmidonta heterodon) and triangle floater (Alasmidonta undulata).
“All of the organisms in a river like the Paulins Kill evolved to live in a cool, flowing, rocky-bottom stream,” Styler Barry told CentralJersey.com. “When you restore flow, the river begins to heal itself.”
A newly released project video captures this transformation in a way that still images and written updates cannot.
Drawing on aerial footage collected by The Nature Conservancy’s Volunteer Drone Team prior to demolition and by Princeton Hydro throughout and after construction, the video documents the full arc of the Paulina Lake Dam removal from initial notching through full demolition and into the restored conditions visible today. The footage provides a comprehensive look at dam removal in practice, illustrating how careful sequencing, sediment management, and adaptive design allow rivers to recover rapidly once barriers are removed.
Beyond ecological gains, the removal of Paulina Lake Dam has significantly improved public safety and community resilience. In CentralJersey.com, Geoffrey M. Goll, PE, President of Princeton Hydro, emphasized the long-term risks associated with aging dams. “If you don’t take care of them, they’ll come out on their own—and that’s a much bigger problem. Once dams are properly removed, people start to see the value of a free-flowing river.”
Many dams were never designed to withstand today’s hydrologic conditions. With climate change driving more frequent and intense rainfall events, proactive removal reduces flood risk, eliminates inspection and maintenance liabilities, and allows rivers to function as more resilient, self-sustaining systems. At the Paulina Lake site, removal has also improved recreational access and restored a more natural landscape for the community.
While the Paulins Kill now flows freely through the former Paulina Lake Dam site, final project phases focus on adaptive management, targeted bank stabilization, habitat feature enhancement, and native tree planting to support long term ecological resilience. As the river continues to adjust and evolve, the Paulina Lake Dam site stands as a clear example of what is possible when outdated infrastructure is thoughtfully removed and natural systems are given the opportunity to recover.
Nestled within the New Jersey townships of Hamilton, Robbinsville, and West Windsor lies Miry Run Dam Site 21—an expansive 279-acre parcel with a rich history dating back to its acquisition by Mercer County in the late 1970s. Originally earmarked for flood mitigation and recreation, this hidden gem is on the cusp of a remarkable transformation, poised to unveil its true potential as a thriving public park.
Central to the revitalization efforts is a comprehensive Master Plan, meticulously crafted by Mercer County Park Commission in partnership with Simone Collins Landscape Architecture and Princeton Hydro. This visionary roadmap encompasses a spectrum of engineering and ecological uplift initiatives, including:
The Master Plan serves as a long-term vision for improvements to the property and will be implemented over multiple phases. In 2021, it was recognized with the Landscape Architectural Chapter Award from the New Jersey Chapter American Society of Landscape Architects, which underscores its innovative and impactful approach to landscape design.
Now, Dam Site 21’s revitalization has begun with a crucial endeavor: the dredging of its 50-acre lake. This process, spearheaded by Mercer County Park Commission in collaboration with Princeton Hydro, aims to rejuvenate the water body by removing accumulated debris, sediment, and invasive vegetation—a vital step towards restoring its ecological balance. Beyond the aesthetic and ecological improvements, dredging enhances accessibility for recreational activities that provide an opportunity to create a deeper connection between the park’s visitors and its beautiful natural landscape.
Based on the bathymetric assessment, which the Princeton Hydro team completed as part of the Master Plan, the dredging efforts are focused on three primary areas: Area 1 is located in the main body of the lake just downstream of Line Road and will generate approximately 34,000 cubic yards of dredged material; Area 2, which has approximately 4,900 cubic yards of accumulated sediment is located in the northeast cove, just north of Area 1; and Area 3, the northwestern cove, entails the removal of approximately 7,300 cubic yards of accumulated sediment.
Before the dredging work could begin, the Princeton Hydro team was responsible for providing a sediment sampling plan, sample collection and laboratory analysis, engineering design plan, preparation and submission of all NJDEP regulatory permitting materials, preparation of the technical specifications, and bid administration. Currently, our team is providing construction administration and oversight for the project.
The journey towards Dam Site 21's revival has been marked by meticulous planning, design, and community engagement spanning several years. With the commencement of dredging operations, the project's vision is gradually materializing—a testament to the dedication of all stakeholders involved. As the first phase unfolds, anticipation mounts for the realization of a vibrant, inclusive public space that honors both nature and community.
As Dam Site 21 undergoes its metamorphosis, it symbolizes not just a physical restoration, but a renewal of collective vision and commitment. Ultimately, Dam Site 21 isn't just a park—it's a testament to the enduring legacy of conservation, community, and the transformative power of restoration.
The significance of Dam Site 21's transformation extends far beyond its recreational appeal. It embodies a commitment to environmental stewardship, with measures aimed at bolstering flood resilience, improving water quality, and nurturing diverse wildlife habitats. By blending conservation with recreation, the project strikes an important balance between creating access for community members to enjoy the space and ecological preservation that puts native plants, critical habitat, and wildlife at the forefront.
To learn more about the restoration initiative and view the Final Master Plan, visit the Mercer County Park Commission’s website. Click here to learn about another one of Princeton Hydro’s recent restoration efforts. And, stay tuned here for more Mercer County Park Commission project updates!
Exciting changes have unfolded at Kol Emet, a Reconstructionist Congregation in Yardley, Bucks County, Pennsylvania. The campus’ exterior lands have undergone a remarkable transformation, blossoming into an enchanting and peaceful place for community member gatherings, and a wildflower meadow.
Princeton Hydro partnered with Congregation Kol Emet to design and implement the synagogue's 10-acre campus transformation. The Princeton Hydro team provided green infrastructure engineering, landscape architecture, and construction services aimed at enhancing the usability and welcoming atmosphere of the synagogue, and creating a sustainable outdoor solution in the event of future pandemics, and a place to connect with the natural environment that surrounds the property. The design provides a net positive impact by reducing flooding in the community and improves water quality by augmenting stormwater management and biodiversity throughout the property.
"Our vision surpassed mere construction of a gathering space," said Geoffrey M. Goll P.E., President of Princeton Hydro, a congregant of Kol Emet, Executive Board Member, and point person for the project. "We wanted to create a harmonious union between the synagogue campus and the surrounding preserved woodlands, cultivating a serene haven where congregants can unite, celebrate, and worship, while also enhancing the ecological functionality and biodiversity of the landscape. This was a realization of the vision of the Founders of Kol Emet and the labor and financial support of many members of the Board, past and present, and a generous donation by a longtime supporter of the community. The outdoor sanctuary was named in honor and memory of a founding member and former President, Geri Shatz, who was a staunch supporter of the Jewish community and advocate for the mission of Kol Emet. She lived the ideals of community and contribution. I am proud of the extraordinary transformation that’s been achieved."
The Kol Emet Reconstructionist Congregation, is a 501(c)3 religious organization, founded in 1984. While a center of worship for its members, it is much more than that. Kol Emet is a community of people who care about improving the world around them through social action and environmental protection.
The sentiment of "Tikkun Olam" is embodied by Kol Emet and the committee that spearheaded the project, working directly with the Princeton Hydro team to bring the project goals to fruition. The modern interpretation of the Hebrew phrase “Tikkun Olam,” is “action intended to repair and improve the world.” The campus restoration project brings the concept of “Tikkun Olam” to life.
Princeton Hydro Landscape Architect Cory Speroff, PLA, ASLA, CBLP is the project’s lead designer. The project included landscape design and planting that incorporates native and sustainable trees and shrubs; significant upgrades to the existing stormwater management basin, including the conversion of low-flow channels, impervious surfaces, and turf-covered areas to native grassland and wildflower habitat; and the development of the “Geri Shatz Outdoor Contemplative Space."
Cory’s design inspiration for the Geri Shatz Outdoor Contemplative Space is modeled after the Hebrew term “etz chaim” or “Tree of Life.” In Judaism, the Tree of Life has a number of meanings, both literal and figurative. In the Kabbalah, the Tree of Life represents the connection between heaven and earth, wisdom and knowledge, and the interconnectedness of all living things. It is visually represented as a diagram that looks much like a tree with 10 nodes and 22 lines. Cory’s design for the community space uses strategically placed trees to mimic the Tree of Life and aims to promote community connection and a connection to the surrounding natural landscape.
The contemplative space consists of a bimah, seating to accommodate at least 80 people, and a beautiful array of native trees and flowering shrubs, including black gum, silver birch, and Virginia sweetspire.
Cory’s design for the land surrounding the contemplative space improves flood resilience; controls stormwater runoff volume and promotes groundwater recharge; boosts safety features of the campus; and enhances habitat for pollinators, native plants, and other important species. The wildflower meadow was seeded with a variety of native plants, including purple love grass, common milkweed, wild bergamot, and blue wild indigo.
“During the height of the COVID-19 pandemic, it felt like the only way to see our loved ones was to be outside, and during these backyard and front porch gatherings many people re-discovered their love for the outdoors,” said Cory. “In talking with the Committee, there was a desire to create an outdoor sanctuary where the congregation could gather and continue that re-discovery. I believe that through the careful consideration of symbolic elements and thoughtful design choices, we’ve created a space that can inspire introspection, connection, and a sense of harmony with both nature and faith.”
Funding for the project came from the Congregation Kol Emet’s “Our Heart. Our Home” capital campaign, a $750,000 campaign focused on upgrading four key aspects of the synagogue: social hall, HVAC upgrades, indoor sanctuary, outside school, and the new outdoor sanctuary. The outdoor sanctuary and ecological uplift to the 10-acre campus is a primary piece of the campaign and was made possible by the generous donations of several Kol Emet members.
Stan Shatz bestowed a bounteous donation in memory of Geri Shatz, which made possible the creation of the “Geri Shatz Outdoor Contemplative Space.”
The following families also contributed to the funding of the Geri Shatz Outdoor Contemplative Space: Laurel & Kevin Bloch, Barbara & Debra Fogel and Family, Jill & David Gordon, Annie & Ryan Kubanoff and Family, and Teddi & Josh Matisoff and Family.
The Princeton Hydro team is honored to have worked with Kol Emet on this important and inspirational project.
Congregation Kol Emet came together on Sunday, June 4, 2023 for a celebration and ribbon-cutting ceremony to mark the completion of the outdoor sanctuary project. Here are a few photos from the joyous event:
Princeton Hydro is an expert in engineering, ecological restoration, and landscape architecture, and we’ve been incorporating green stormwater infrastructure and nature-based solutions into our designs for decades. Click here to read about the landscape restoration and stormwater management project we designed and implemented in Thompson Park, a 675-acre recreation area in Middlesex County, New Jersey.
In the late 1920s, the U.S. government began allocating funds for road construction in U.S. national forests. This led to hundreds of thousands of culverts being built and installed across the country for the purpose of moving water quickly and efficiently underneath the roadways to prevent flooding, minimize erosion, and provide pathways for stormwater.
However, culverts have had an unintended and significant consequence: they block the migration routes of some fish and aquatic organisms.
Culverts that are undersized, improperly placed, or designed with smooth featureless surfaces can impede or totally block fish and aquatic species from passing. Culverts with extremely high velocity flows make it incredibly difficult for aquatic organisms to navigate upstream, and extremely low velocity flows make it hard for fish to pass in either direction. The high-velocity flows can erode the stream channel immediately downstream of the culvert, which can leave the culvert pipe perched. This elevation above the water channel makes it impossible for organisms to pass through. Debris can also collect in the culvert, not only blocking fish passage, but water as well.
In addition to blocking the upstream passage of fish and other aquatic species, some culverts disrupt the normal stream movements of some macroinvertebrates, which are key components of these stream ecosystems, an important food source to countless species, and play a critical role in the cycling of energy and nutrients throughout stream ecosystems. Disruptions to the movement and dispersal of stream macroinvertebrates can reduce available habitat, lead to genetic isolation of some populations, and cause extirpation of critical species. When populations splinter, it causes a reduction in genetic diversity, which can lead to the spread of more invasive species and many other ecological issues.
While culverts serve an important function in road construction and flood prevention, their impact on aquatic organisms must be taken into consideration. Finding solutions that both allow for efficient water flow and enable safe aquatic migration is crucial in preserving the health of our waterways and their ecosystems.
A shift in the 1980s recognized the importance of redesigning road-stream crossings for several reasons, including restoring aquatic organism passage and maintaining flood resilience. Between 2008 and 2015, U.S. Forest Service (USFS) partnered with more than 200 organizations in the Legacy Roads and Trails Program to replace 1,000+ culverts across the country. The aim of the program was to upgrade culverts to emulate natural streams and to allow fish and wildlife to pass more naturally both upstream and downstream.
Replacing culverts with structures that better facilitate the movement of both water and aquatic organisms has benefits beyond restoring critical ecosystems and improving biodiversity. Ecological restoration creates jobs, stimulates outdoor recreation and local economic activity, and generates long-term economic value.
Princeton Hydro has a strong history in designing connectivity-friendly road-stream crossings and restoring/replacing outdated culverts. Our team of engineers and scientists has been directly involved with hundreds of stream and ecosystem restoration projects throughout the Northeast.
For several years, Princeton Hydro has partnered with NY-NJ Harbor & Estuary Program (HEP) to plan and design for aquatic connectivity through climate-ready infrastructure. Created by the U.S. Environmental Protection Agency (USEPA) at the request of the governors of New York and New Jersey, HEP develops and implements plans that protect, conserve and restore the estuary, and aquatic connectivity is a key focus area for HEP and its partners.
Most recently, HEP partnered with Princeton Hydro to address hydraulic capacity issues at priority road-stream crossings in New Jersey’s South River and Lower Raritan River watersheds. The Princeton Hydro team developed a 30% engineering plan for a priority road-stream crossing – the Birch Street crossing over the Iresick Brook in Old Bridge, NJ.
Iresick Brook is upstream from Duhernal Lake, located at the end of the free-flowing South River, which feeds into the Raritan River, and ultimately flows into Raritan Bay. Duhernal Lake is dammed at the outlet so there is little to no connectivity downstream from the Iresick Brook sub-watershed. The watershed is highly dendritic (meaning the drainage pattern follows a tree-like shape) with many small streams running through it, some of them ephemeral.
The Iresick Brook 5 (IB5) culvert, located in Old Bridge Township, New Jersey, is an undersized double culvert in poor condition with an eroding streambank. This culvert was chosen as a restoration priority primarily due its inadequate sizing (both pipes are only 3-feet in diameter). The outdated infrastructure blocks the passage of fish and other aquatic organisms, and it can only accommodate a 50-year storm event.
Once the IB5 culvert was identified as the priority site, Princeton Hydro completed a site investigation, which included a geomorphic assessment, site observations, and simplified site survey of the channel alignment, profile, and cross sections both upstream and downstream of the culvert.
At the time of the survey, flow was only a couple inches deep in the channel and incredibly slow-moving, especially in the upstream reach. Despite the low flow at the time of the survey, during storm events, the stream experiences extremely high velocities. The undersized culvert creates hydraulic constriction and subsequently a velocity barrier that prevents passage. Additionally, when the high-flow stream water is forced through the small pipes, it creates a firehose effect, which has led to the formation of a 60-foot-long scour hole at the culvert outlet. Substrate from the scour hole has been washed downstream, forming an island of large sand and small gravel.
Approximately 155 feet upstream of the culvert is a channel-spanning v-notch weir comprised of a combination of sheet pile and timber. The weir appears to be a historical stream gauge that is highly degraded and creates an artificially perched channel. The upstream channel also contains woody debris, which gets caught at the culvert, blocking water flow and organism passage.
For the design process, Princeton Hydro used the USFS Stream Simulation Design, an gold-standard ecosystem-based approach for designing and constructing road-stream crossings that provide unimpeded fish and other aquatic organism passage through the structure. The Stream Simulation, a required standard on USFS road projects, integrates fluvial geomorphology concepts and methods with engineering principles to design a road-stream crossing that contains a natural and dynamic channel through the structure so that fish and other aquatic organisms will experience no greater difficulty moving through the structure than if the crossing did not exist.
The design also incorporated utility constraints (gas line, sewer line, drinking water main, and stormwater outlet), a longitudinal profile assessment, channel capacity and slope analysis, and a simplified hydrologic & hydraulic assessment.
Ultimately, Princeton Hydro recommended that HEP replace the existing culvert with a Contech Precast O-321 culvert, or similar alternative. The proposed design increases the culvert opening area and allows for significant increases in flow capacity. This culvert replacement project has the potential to reduce local flood risk and restore aquatic organism passage to the reach of Iresick Brook.
Aquatic connectivity is crucial for improving healthy aquatic ecosystems and managing severe storms and flooding. Increases in rainfall due to climate change makes investing in these improvements even more of a growing priority. With so many culverts in place, it can be difficult to know which culvert restoration projects to prioritize.
We worked with HEP to create a toolkit for addressing problematic road-stream crossings. The easy-to-use matrix helps to prioritize potential projects and identify solutions for problem culverts and relative cost solutions.
The toolkit was just recently released to the public with the hope that it will be used as a template to promote the development of more resilient and environmentally-friendly infrastructure.
Click here to get more info and download.
If you've ever observed orange water in a river or stream after a dam has been removed, you may have been surprised by the strange color. This phenomenon is caused by iron oxide floc. But what exactly is iron oxide floc and how does it form?
Iron oxide, also known as rust, is a common compond found in nature. When it is dissolved in water, it takes on a reddish-brown color. Although the color can be alarming, iron oxide floc is relatively harmless and is actually a sign of the waterway returning to a more natural state.
The formation of iron oxide floc begins with the seepage of anaerobic groundwater through the embankment of a dam. The groundwater behind a dam often contains high levels of iron and is anaerobic (low in oxygen) because it is not exposed to the air and therefore does not have access to oxygen. When this anaerobic water reaches the other side of the dam and mixes with the aerobic surface water, the oxygen in the surface water reacts with the iron in the groundwater, forming iron oxide floc.
The orange color of the water is a result of the floc suspending in the water column and/or settling to the bottom of the waterway, creating a layer of orange sediment. In these situations, the iron oxide floc is only a temporary effect of the dam removal, not harmful to the environment, and will eventually be washed away by natural processes. As the waterway adjusts to its new, natural flow, the iron oxide floc will eventually disappear completely.
While the orange color may be surprising to see, it is a sign that the waterway is returning to a more natural state, leading to the water quality and habitat improvements achieved by dam removals. Removing outdated dams and restoring the natural flow of rivers has myriad benefits, including reconnecting river habitats that benefit fish and wildlife; reducing flood risk to surrounding communities; and promoting a healthier and more diverse ecosystem.
Princeton Hydro has designed, permitted, and overseen the removal of dozens of small and large dams throughout the Northeast. Click here to learn more about our dam engineering and removal services. And, if you're interested in reading about some of the dams we've removed in the Lehigh River Valley, click below:
According to American Rivers, “more than 90,000 dams in the country are no longer serving the purpose that they were built to provide decades or centuries ago.” As these dams age and decay, they can become public safety hazards, presenting a failure risk and flooding danger. Dams can also be environmental hazards, blocking the movement of fish and other aquatic species, inundating river habitat, impairing water quality, and altering the flow necessary to sustain river life.
Removing nonfunctional, outdated dams has myriad ecological benefits. Dam removal can improve water quality, restore a river back to its natural flowing state, reconnect river habitats that benefit fish and wildlife, and significantly increase biodiversity for the surrounding watershed.
For over a decade, Princeton Hydro has partnered with Wildlands Conservancy to remove dams in the Lehigh River Valley. Wildlands Conservancy, a nonprofit land trust in eastern Pennsylvania, works to restore degraded stream and wildlife habitat with a primary focus on Lehigh Valley and the Lehigh River watershed, which is a 1,345 square mile drainage area that eventually flows into the Delaware River.
Wildlands Conservancy contracted Princeton Hydro to design and permit the removal of two dams on the Little Lehigh Creek. Although it is referred to as the “Little Lehigh,” the 24-mile creek is the largest tributary of the Lehigh River. The dam removals restored the natural stream system, which hadn’t flowed freely in over a century.
Princeton Hydro also worked with Wildlands Conservancy to remove several barriers and three consecutive low-head dams on Jordan Creek, a tributary of the Little Lehigh Creek. Jordan Creek arises from a natural spring on Blue Mountain, and eventually joins the Little Lehigh in Allentown before flowing into the Lehigh River. It drains an area of 75.8 square miles.
Collectively, these dam and barrier removal projects on the Little Lehigh and Jordan Creek reconnected 15+ miles of river; restored fish passage; improved aquatic connectivity, fisheries, and benthic macroinvertebrate and wildlife habitats; reduced nonpoint source stormwater pollution; improved water quality; addressed vulnerable infrastructure; enhanced climate resiliency; and stabilized and restored the creeks’ channels and banks.
Building upon the successes of the Little Lehigh and Jordan Creek barrier removals, Princeton Hydro is again partnering with Wildlands Conservancy to remove three consecutive dams on Bushkill Creek in Easton, PA. The dam removal projects, which are slated for 2023, are part of a large-scale effort, involving a significant number of community and municipal partners, focused on restoring Bushkill Creek and the surrounding watershed.
The Bushkill Creek is a 22-mile long limestone stream that is designated as a “high quality, cold-water fishery.” It supports healthy populations of trout, and is treasured by anglers and the surrounding community as an important resource in an urban environment, spanning several boroughs and townships, eventually flowing into the Delaware River at Easton.
Environmental protection and restoration is a key goal of removing the dams. Removing these barriers will allow important migratory fish species to reach their spawning grounds once again, which has numerous and far-reaching ecological benefits. The project work also includes stabilizing the streambank, planting, and expanding riparian buffers, planting native trees and shrubs to filter runoff, and installing in-stream structures to restore fish habitat.
Princeton Hydro has designed, permitted, and overseen the reconstruction, repair, and removal of over 60 of small and large dams in the Northeast. To learn more about our fish passage and dam removal engineering services, click here. To learn more about Wildlands Conservancy, click here.
As part of the multi-faceted effort to restore the vital Hudson River ecosystem, the USACE New York District launched the Hudson River Habitat Restoration. Princeton Hydro led the Hudson River Habitat Restoration Integrated Feasibility Study and Environmental Assessment for USACE. For this project, we established and evaluated baseline conditions through data collection and analysis; developed restoration objectives and opportunities; prepared an Environmental Assessment; and designed conceptual restoration plans for eight sites.
This week, Lt. Gen. Scott A. Spellmon, USACE Commanding General and 55th U.S. Army Chief of Engineers, signed the Hudson River Habitat Restoration Ecosystem Restoration Chief’s Report, which represents the completion of the study and makes it eligible for congressional authorization.
As stated in the USACE-issued news release, “The Chief’s Report recommends three individual ecosystem restoration projects including Henry Hudson Park, Schodack Island Park, and Moodna Creek within the 125-mile study area from the Federal Lock and Dam at Troy, NY to the Governor Mario M. Cuomo Bridge. These projects would restore a total of approximately 22.8 acres of tidal wetlands, 8.5 acres of side-channel and wetland complex, and 1,760 linear feet of living shoreline with 0.6 acres of tidal wetlands. The plan would also reconnect 7.8 miles of tributary habitat to the Hudson River through the removal of 3 barriers along Moodna Creek.”
“The signing of this Chief’s Report is a significant milestone for the HRHR Project,” said Col. Matthew Luzzatto, USACE New York District Commander. “This has truly been a team effort and I want to thank our non-federal sponsors, New York State Department of Environmental Conservation and New York State Department of State, and all of our engineers, scientists, and partners at the local, state and federal level for their unwavering support.”
Read the full press release here. And, for more background information on the Feasibility Study and proposed restoration work, check out our original blog post:
The City of Linden, located 13 miles southwest of Manhattan in Union County, New Jersey, is a highly urbanized area with a complex mix of residential, commercial, and industrial land uses. Originally settled as farmland on broad marshes, the City has deep roots in industrial production that emerged in the 19th century, and its easily accessible location on the Arthur Kill tidal straight helped fuel this industrial development.
Now, the City of Linden, which is home to more than 40,000 people, is considered a transportation hub: it has three major highways running through it (the New Jersey Turnpike, Route 1, and Route 27); its rail station provides critical commuter and industry access; the Linden Municipal Airport is a gateway to the NY/NJ metropolitan area; and its access point on the Arthur Kill is used by shipping traffic to the Port Authority of NY and NJ.
Unfortunately, the industrial boom left a legacy of pollution in the city, so much, that the Tremley Point Alliance submited an official Envionmental Justice Petition to the state. In 2005, the New Jersey Environmental Task Force selected the community for the development of an Environmental Justice Action Plan and listed it as one of six environmental justice communites in New Jersey.
Like other communities in the Arthur Kill Watershed, Linden also suffers severe flooding from heavy rains and storms with one of the significant sources of flood water coming from stormwater runoff. Due to a high percentage of impervious cover from houses, roadways, and sidewalks, even small rain events generate a significant amount of stormwater runoff. Over time, these conditions have been exacerbated by the historic loss of coastal wetlands and outdated infrastructure. Nuisance flooding is especially problematic as runoff cannot drain from the area at a sufficient rate to prevent flooding during normal or elevated tidal conditions. Very simply, heavy rainfall is one factor contributing to recurring flooding.
In 2012, Hurricane Sandy caused wide-spread destruction throughout New Jersey and the entire eastern seaboard. The City of Linden was hard hit, and the City’s Tremley Point neighborhood was especially storm-ravaged. Tremley Point, a low-lying community of about 275 homes located at the headwaters of Marshes Creek and in the 100-year floodplain of the Rahway River, is regularly flooded during normal rain events. During Hurricane Sandy, local news outlets reported that a 15-foot tidal surge overtook Tremley Point homes, destroyed roads, and washed up hazardous material such as a 150-gallon diesel tank.
To help communities like Tremley Point recover, the New Jersey Department of Environmental Protection (NJDEP) launched the Blue Acres program under which NJDEP purchases homes from willing sellers at pre-Sandy market values, so residents in areas of repetitive and catastrophic flooding can rebuild their lives outside flood-prone areas. Structures are demolished and the properties are permanently preserved as open space for recreation or conservation purposes. The program began in 1995 and expanded with federal funding after Sandy. The goal of the Blue Acres Program is to dramatically reduce the risk of future catastrophic flood damage and to help families to move out of harm’s way.
As part of the NJDEP Blue Acres Program, Princeton Hydro, in collaboration with the City of Linden, Rutgers University, NJDEP, Phillips 66, National Fish and Wildlife Foundation, New Jersey Corporate Wetlands Restoration Partnership, and Enviroscapes, has undertaken one of the first ecological restoration projects within Blue Acres-acquired properties, which are located in the Tremley Point neighborhood. This project increases storm resiliency by reducing flooding and stormwater runoff by improving the ecological and floodplain function within the former residential properties acquired by the NJDEP Blue Acres Program.
The project includes the development and implementation of an on-the-ground green infrastructure-focused floodplain enhancement design involving the restoration of native coastal floodplain forest and meadow, as well as floodplain wetlands. The restored area provides natural buffering to storm surge and enhances floodplain functions to capture, infiltrate, store, and slow excess stormwater to reduce the risk of future flood damage. In addition, it restores natural habitat and provides public recreation access on NJDEP Blue Acres property.
The design includes re-planting the parcels and the installation of a walking path through part of the area. It also includes the creation of a floodplain bench for the adjacent drainage ditch, an unnamed tributary to Marshes Creek. A floodplain bench is a low-lying area adjacent to a stream or river constructed to allow for regular flooding in these areas. Site improvements include grading of the floodplain bench and minor depressional area; 6-12-inches of tilling, soil amendment, and planting within the planting area; and construction of the gravel pathway.
The project will result in valuable environmental and community benefits to the area, including an annual reduction in stormwater runoff of 4.1 million gallons. This represents a 45% reduction in stormwater runoff. Restoration of the floodplain will also help reduce community vulnerability to storms. The hope is that this project will be a model that fosters more floodplain restoration projects in the future.
For more information on the Blue Acres Program, please visit the DEP website.
The Hudson River originates at the Lake Tear of the Clouds in the Adirondack Mountains at an elevation of 4,322 feet above sea level. The river then flows southward 315 miles to New York City and empties into the New York Harbor leading to the Atlantic Ocean. The Hudson River Valley lies almost entirely within the state of New York, except for its last 22 miles, where it serves as the boundary between New York and New Jersey.
Approximately 153 miles of the Hudson River, between the Troy Dam to the Atlantic Ocean, is an estuary. An estuary is defined by the USEPA as “a partially enclosed, coastal water body where freshwater from rivers and streams mixes with salt water from the ocean. Estuaries, and their surrounding lands, are places of transition from land to sea. Although influenced by the tides, they are protected from the full force of ocean waves, winds and storms by landforms such as barrier islands or peninsulas.”
The Hudson River’s estuary encompasses regionally significant habitat for anadromous fish and globally rare tidal freshwater wetland communities and plants, and also supports significant wildlife concentrations. As a whole, the Hudson River provides a unique ecosystem with highly diverse habitats for approximately 85% of New York State’s fish and wildlife species, including over 200 fish species that rely on the Hudson River for spawning, nursery, and forage habitat.
The Hudson is an integral part of New York’s identity and plays a vital role in the lives of the people throughout the area. Long valued as a transportation corridor for the region’s agricultural and industrial goods, and heavily used by the recreation and tourism industries, the Hudson plays a major role in the local economy. It also provides drinking water for more than 100,000 people.
At the end of the American Revolution, the population in the Hudson River Valley began to grow. The introduction of railroad travel in 1851 further accelerated development in the area. Industrial buildings were erected along the river, such as brick and cement manufacturing, which was followed by residential building. Along with the aforementioned development, came the construction of approximately 1,600 dams and thousands of culverts throughout the Hudson River.
According to the U.S. Army Corps of Engineers (USACE), these human activities have significantly degraded the integrity of the Hudson River ecosystem and cumulatively changed the morphology and hydrology of the river. Over time, these changes have resulted in large-scale losses of critical shallow water and intertidal wetland habitats, and fragmented and disconnected habitats for migratory and other species. Most of this loss and impact has occurred in the upper third portion of the estuary.
As part of the effort to restore the vital river ecosystem, the USACE New York District launched a Hudson River Habitat Restoration Feasibility Study, which helps to establish and evaluate baseline conditions, develop restoration goals and objectives, and identify key restoration opportunities. Princeton Hydro participated in data collection and analysis, conceptual restoration designs, and preparation of the USACE Environmental Assessment for the Hudson River Habitat Restoration Ecosystem Restoration Draft Integrated Feasibility Study and Environmental Assessment.
The study area includes the Hudson River Valley from the Governor Mario M. Cuomo Bridge downstream to the Troy Lock and Dam upstream. The primary restoration objectives include restoring a mosaic of interconnected, large river habitats and restoring lost connectivity between the Hudson River and adjacent ecosystems.
A total of six sites were evaluated using topographic surveys, installation and monitoring of tide gauges, evaluation of dam and fish barrier infrastructure, and field data collection and analysis to support Evaluation of Planned Wetlands (EPW) and Habitat Suitability Indices (HSI) functional assessment models. Literature reviews were also completed for geotechnical, hazardous toxicity radioactive waste, and aquatic organism passage measures.
Multiple alternatives for each of the six sites were created in addition to the preparation of conceptual designs, quantity take-offs, and cost estimates for construction, monitoring and adaptive management, and long-term operation and maintenance activities.
Princeton Hydro also prepared an environmental assessment in accordance with NEPA standards, addressing all six sites along the Hudson River and its tributaries. This assessment served to characterize existing conditions, environmental impacts of the preferred Proposed Action and No Action Alternatives, and regional cumulative environmental impacts. Our final report was highlighted by USACE at the 2019 Planning Community of Practice (PCoP) national workshop at the Kansas City District as an example of a successfully implemented Ecosystem Restoration Planning Center of Expertise (ECO-PCX) project.
USACE’s specific interest in Hudson River restoration stems from the aforementioned dramatic losses of regional ecosystems, the national significance of those ecosystems, and the apparent and significant opportunity for measurable improvement to the degraded ecological resources in the river basin.
The feasibility study is among the first of several critical steps in restoring the Hudson River’s ecosystem function and dynamic processes, and reestablishing the attributes of a natural, functioning, and self-regulated river system. Stay tuned for more updates on the Hudson River restoration efforts.
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Sinkholes can be quite terrifying. We see them on the news, on television and in movies seemingly appearing out of nowhere, swallowing up cars and creating calamity in towns across the world. In this two-part blog series, our experts uncover the mystery around sinkholes and arm you with the facts you need to make them less scary.
In part one of the blog series, we discuss what a sinkhole is, three different types of sinkholes, and what causes them to form. In this second part, we explore how to detect sinkholes, what to do if you detect a sinkhole, and the steps taken to repair them.
Not all sinkholes are Hollywood-style monstrosities capable of swallowing your whole house. But even a much smaller, less noticeable sinkhole can do its fair share of harm, compromising your foundation and damaging utilities.
Although sinkholes can be scary to think about, you can take comfort in knowing there are ways to detect them, both visually and experimentally. Often, you can spot the effects of a developing sinkhole before you can spot the hole itself. If you live in an area with characteristics common to sinkhole formation (i.e. “karst terrain,” or types of rocks that can easily be dissolved by groundwater), there are some things you can do to check your property for signs of potential sinkhole formation.
According to the American Society of Home Inspectors, there are key signs you should be on the lookout for in and around your home:
If you spot any of the signs listed above, or you suspect that you have a sinkhole on or near your property, you should contact your township, public works, or the local engineering firm that represents your municipality right away. If you have discovered a sinkhole that is threatening your house or another structure, be sure to get out immediately to avoid a potentially dangerous situation.
If you’re trying to determine whether or not you have a sinkhole on your property, there are a few physical tests that can be conducted to determine the best course of action.
Electro-resistivity testing: This extremely technical test can best be summed up by saying it uses electrodes to determine the conductivity of the soil. Since electricity can’t pass through air, this test shows any pockets where the current didn’t pass through. This is a fairly accurate way to determine if there is a sinkhole and where it is.
Micro-gravity testing: Another incredibly technical method, this test uses sensors that detect the measure of gravity. Since the gravitational pull in a given area should be the same, you can see if there are minute differences in the measurement. If there is a difference, then it’s likely that you have a sinkhole in that area.
If you are still unsure whether or not you live in a sinkhole risk area, you can check with your local, territorial, or national government offices; review geological surveys such as the United States Geological Survey (USGS); and contact an expert.
There are three main techniques experts utilize to repair sinkholes. The type of sinkhole and landowner's aesthetic preferences determine the methodology used to repair the sinkhole.
Our engineers regularly go out in the field to oversee and inspect sinkhole repairs. If you detect a sinkhole, or what might be a sinkhole, on your property, our experts strongly advise immediate actions be taken. Ignoring a sinkhole will only cause it to get larger and more dangerous as time passes, and putting topsoil over a sinkhole will only exacerbate the symptoms.
While there’s really no way to prevent a sinkhole, you can never be too prepared! Here are three easy steps you can take to determine if you live in or around a sinkhole-prone area and what to do in the event of a surprise sinkhole:
Although scary, sinkholes are a manageable threat if you’re informed and prepared. After all, it is possible to do something about sinkholes – if they can be detected in time.
Special thanks to Princeton Hydro Staff Engineer Stephen Duda, Geologist Marshall Thomas, and Communications Intern Rebecca Burrell for their assistance in developing this blog series.
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