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In urban areas, streams have often been buried beneath streets, buildings, and infrastructure, cutting them off from the natural ecosystem. However, a growing movement towards "daylighting" streams—uncovering and restoring these buried watercourses—has proven to be an innovative solution for improving water quality, reducing flood risks, restoring fish passage, and creating healthier habitats. Princeton Hydro has been at the forefront of these efforts, bringing expertise in ecological restoration and water resource management to daylighting projects across New Jersey.
Daylighting is the process of removing obstructions and impervious surfaces from a buried stream or river, restoring it to a more natural state. Often, streams were diverted underground to make way for urban development. Daylighting involves reversing this process, bringing the water flow back above ground where it can interact with the natural environment. The result is a newly visible, revitalized waterway that reconnects the stream to its surrounding ecosystem. This process not only improves stormwater management but also enhances urban spaces and promotes healthier habitats.
Daylighting streams offers numerous advantages to both the environment and local communities. Some key benefits include:
Princeton Hydro has successfully completed numerous daylighting projects that demonstrate the transformative power of restoring natural waterways. By leveraging innovative engineering and ecological practices, these projects restored the natural flow of waterways and enhanced the surrounding landscape. Let’s take a closer look at two examples:
In the heart of Trenton, NJ, Princeton Hydro undertook a comprehensive stream restoration. The City of Trenton, as part of a larger urban revitalization and brownfield redevelopment project, sought to restore the stream, Petty’s Run, which had long suffered from typical urban afflictions: pollution, flooding, and heavy debris accumulation.
Princeton Hydro developed a green infrastructure design that addressed these challenges holistically. The design included removing from the stream channel heavy debris, contaminated soils, and the concrete remains of previous development. The team also replaced the restrictive upstream road crossing with a pedestrian bridge, enhancing both the stream’s flow and the community’s connectivity. A significant aspect of the project involved daylighting the 250-foot underground portion of Petty’s Run, restoring it to a natural, open flow while creating an adjacent floodplain meadow to manage stormwater and provide habitat.
The project improved stormwater management, enhanced the landscape’s biodiversity, added habitat value, and established a new public green space with walking trails, which now serves as both an ecological asset and a recreational area for the community. This project earned both the Phoenix Award for Brownfield Redevelopment and the Bowman’s Hill Land Ethics Award.
Thompson Park, a sprawling 675-acre recreational area in Middlesex County, NJ, boasts a variety of amenities, including hiking trails, ballfields, and a zoo that is home to over 50 geese and fowl, goats, and approximately 90 deer. The streams within the park faced challenges, particularly in the areas surrounding the zoo’s enclosures, including erosion and compromised water quality.
In order to increase channel stability, decrease erosion, improve water quality and ecological function, and reduce the pollutants originating from the zoo, a stormwater management treatment train was designed and constructed.
Middlesex County Office of Parks and Recreation and Office of Planning, New Jersey Department of Environmental Protection, South Jersey Resource Conservation and Development Council, Middlesex County Mosquito Extermination Commission, Freehold Soil Conservation District, Rutgers Cooperative Extension, Enviroscapes and Princeton Hydro worked together to fund, design, permit, and construct numerous stormwater management measures within Thompson Park.
One of the key project initiatives involved daylighting a section of a 24-inch reinforced concrete pipe (RCP) that had previously conveyed stormwater underground. Daylighting the stream, widen the stream channel, improved stormwater absorption, reduced erosion, helped restore the stream’s natural gradient, and improved aquatic habitat.
This multi-faceted restoration project improved stream function and created a more sustainable environment for both zoo inhabitants, the park’s visitors, and the watershed.
Princeton Hydro’s President and Founding Principal, Geoffrey M. Goll, PE, recently shared his expertise in stream restoration during a "Daylighting Streams: Design & Engineering" webinar hosted by The Watershed Institute. The webinar explored the process of uncovering and restoring buried watercourses. Moderated by Susan Bristol, The Watershed Institute Municipal Policy Specialist, the webinar featured experts Vince Sortman, Biohabitats Senior Fluvial Geomorphologist; Warren T. Byrd, Jr., FASLA, Founding Partner of Nelson Byrd Woltz Landscape Architects & Professor Emeritus, University of Virginia; and Geoffrey. The webinar provided valuable insights into the challenges and benefits of these projects, highlighting the importance of hazard mitigation, maintenance, and community involvement in successful daylighting initiatives. The event underscored the significance of daylighting in enhancing both urban infrastructure and natural ecosystems.
Daylighting streams is a forward-thinking approach to urban water management that brings immense benefits to the environment and local communities. As daylighting continues to gain recognition as an essential tool for watershed restoration, Princeton Hydro remains a trusted leader in the field, combining innovative design with environmental stewardship.
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.
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 – not to mention, many of these culverts are located in river headwaters – it can be very challenging to know which culvert restoration projects to prioritize.
Princeton Hydro partnered with New York - New Jersey Harbor & Estuary Program (HEP) and the Hudson River Foundation 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 is meant to be used by a wide audience of professionals and volunteers, including those familiar with the North America Aquatic Connectivity Collaborative (NAACC) protocol for assessing road stream crossings. It builds on the data collected through the NAACC (or similar) field assessments to identify the least expensive & highest priority project sites and provide solutions ranging from low-tech solutions that can be implemented by volunteers at minor blockages, to detailed engineering and construction plans that would require qualified contractors to implement at severe blockages.
Read the full description and download the toolkit now by clicking below:
In March 2020, NJ Department of Environmental Protection (NJDEP) published the long-awaited revisions to the New Jersey Stormwater Management Rule (N.J.A.C. 7:8), which now requires the use of green infrastructure. But what do these updates actually mean for New Jersey’s stormwater infrastructure?
At Princeton Hydro, we recognize the benefit of green infrastructure and we've been incorporating it into our engineering designs since before the term was regularly used in the stormwater lexicon. We've been following the rule amendments very closely, so we’ve got the inside scoop on how to interpret these new updates. In this blog, we’ll break down the complexities and changes to help you understand what’s really going on.
So, let’s start with what green infrastructure actually is in a general sense. Many people think of green infrastructure solely as a way to classify certain stormwater best management practices, or BMPs, but in reality, it goes much deeper than that. Green infrastructure is an approach to engineering design that emphasizes the use of natural processes. Examples include green roofs, rain gardens, constructed wetlands, vegetated bioswales, and living shorelines. In general, approaching environmental management from this lens can help reduce costs and negative impacts to our ecosystems. The benefit to using green infrastructure over structural grey infrastructure is that these living BMPs are incredibly resilient. Being living systems, green infrastructure BMPs help decrease stormwater volume, as soil and vegetation naturally retain and evapotranspire water. Afterall, those natural processes have successfully worked for billions of years, so why not mimic them in our design?
In addition to effectively managing stormwater, green infrastructure has other added benefits such as reducing the heat island effect, reducing energy use, removing pollutants from the air, beautifying public spaces, and even increasing property value. Though the actual practice of green infrastructure may seem new and innovative, the concept has been around for decades.
So now, let’s get to the updated regulations. The biggest takeaway from this update is that green infrastructure is now required to meet the three performance criteria that NJDEP sets forth for stormwater management. The amendments to the rule give definitions of green infrastructure as it applies to stormwater management. The rule defines green infrastructure as follows:
"‘Green Infrastructure’ means a stormwater management measure that manages stormwater close to its source by:
Treating stormwater runoff through infiltration into subsoil;
Treating stormwater runoff through filtration by vegetation or soil; or
Storing stormwater runoff for reuse.”
NJDEP evaluates stormwater management compliance through three basic performance metrics: (1) groundwater recharge, (2) water quality, and (3) peak flow control. While these metrics have remained relatively unchanged under the amended rule, the requirements for meeting them have been modified to include green infrastructure. The pre-existing rule required that major developments incorporate nonstructural stormwater management BMPs/strategies to the “maximum extent practicable” to meet their criteria. The amended rule not only gives specific suggestions for the kind of BMPs it's looking for by adding a definition of green infrastructure, but it also makes those BMPs/strategies a requirement for compliance with the rule’s minimum standards.
The rule also includes tables outlining/summarizing the application of each type of stormwater BMP. One of the biggest changes here is that some of those BMPs have drainage area limitations, which could pose new challenges in the design process.
As stated above, the rule defines green infrastructure as, “a stormwater management measure that manages stormwater close to its source.” This is where those drainage area limitations come into play. Dry wells have a one acre drainage area limitation, which is not new, however, pervious pavement has a 3:1 ratio requirement, meaning that the water flowing over standard pavement, or impervious surfaces, should not be more than three times greater than the area of the pervious pavement.
Likewise, in the amended rule, BMPs like bioretention systems, have a drainage area limitation of 2.5 acres. The addition of this requirement will require designers to spread BMPs out throughout their site, instead of simply including one large structural BMP in a single location on the site. This approach decentralizes and distributes BMPs, enabling more stormwater to infiltrate into the ground, rather than runoff. Because this method more clostely mimics the natural water cycle, it is expected to foster better long-term performance of the BMPs.
This 2.5-acre drainage area limitation is going to effect stormwater design in that it will lead to BMP decentralization. So, project sites will likely have numerous smaller BMPs that will be distributed throughout the area, as opposed to having one large basin at the bottom of the site. This applies, in particular, to large scale commercial and residential projects, as the updated rule will discourage, and in most cases actually not allow, for the implementation of one large basin at the bottom of the site, which currently is common practice in large-scale development design.
Another update to the rule is that motor vehicle surfaces are now incorporated into the definition of major development, which was further clarified and defined as:
“Any individual ‘development,’ as well as multiple developments that individually or collectively result in:
The disturbance of one or more acres of land since February 2, 2004;
The creation of one-quarter acre or more of “regulated impervious surface” since February 2, 2004;
The creation of one-quarter acre or more of “regulated motor vehicle surface” since March 2,2021; or
A combination of 2 and 3 above that totals an area of one-quarter acre or more. The same surface shall not be counted twice when determining if the combination area equals one quarter acre or more.”
The amended rule requires these motor vehicle surfaces to have 80% total suspended solids (TSS) removal, in order to maintain water quality. These surfaces include standard pavement drive/parking areas and gravel and dirt drive/parking areas, according to the rule. However, the rule does not require water quality control for runoff from other impervious surfaces that are not traveled by automobiles, such as rooftops and sidewalks, or other paved walkway areas.
In addition to the changes made to the actual rule, NJDEP released an updated draft of Chapters 5, 12, 13, and Appendix D of the NJ Stormwater BMP Manual, which is currently open for public comment. Chapter 5 regards Stormwater Management and Quantity and Quality Standards and Computations and Chapter 12 regards Soil Testing Criteria. The biggest update to the manual is the addition of the recently finalized Chapter 13: Groundwater Table Hydraulic Impact Assessments for Infiltration BMPs, which requires design engineers to assess the hydraulic impact on the groundwater table to avoid adverse impacts such as surficial ponding, flooding of basements, interference with sewage disposal systems, and interference with the proper functioning of the BMP itself. The addition of this chapter will ensure that these issues are minimized, helping to improve the state’s stormwater management practices overall.
New Jersey municipalities will need to comply with the new standards, as the NJ Stormwater Management Rule represents the minimum requirements for stormwater control ordinances. The law states that municipalities must update their ordinances by March 2, 2021. To make this transition a bit smoother, NJDEP has released a revised model ordinance in Appendix D of the NJ Stormwater BMP Manual to act as a sample for municipalities to follow when adopting these new regulations. Similar to before, municipalities do have the ability to require stricter stormwater performance metrics, but the criteria outlined in the rule are the minimum that must be met under the new regulations.
For more information on the updates to the stormwater regulations, you can check out an informational webinar (below) hosted by NJ-AWRA and The Watershed Institute. This webinar includes three presentations by New Jersey stormwater experts, including our Director of Stormwater Management & Green Infrastructure, Dr. Clay Emerson, PE, CFM.
Hydrology is the study of the properties, distribution, and effects of water on the Earth’s surface, in the soil and underlying rocks, and in the atmosphere. The hydrologic cycle includes all of the ways in which water cycles from land to the atmosphere and back. Hydrologists study natural water-related events such as drought, rainfall, stormwater runoff, and floods, as well as how to predict and manage such events. On the application side, hydrology provides basic laws, equations, algorithms, procedures, and modeling of these events.
Hydraulics is the study of the mechanical behavior of water in physical systems. In engineering terms, hydraulics is the analysis of how surface and subsurface waters move from one point to the next, such as calculating the depth of flow in a pipe or open channel. Hydraulic analysis is used to evaluate flow in rivers, streams, stormwater management networks, sewers, and much more.
Combined hydrologic and hydraulic data, tools, and models are used for analyzing the impacts that waterflow - precipitation, stormwater, floods, and severe storms - will have on the existing infrastructure. This information is also used to make future land-use decisions and improvements that will work within the constraints of the hydrologic cycle and won’t exacerbate flooding or cause water quality impairment.
Simply put, hydrologic and hydraulic modeling is an essential component of any effective flood risk management plan.
Eastwick, a low-lying urbanized neighborhood in Southwest Philadelphia, is located in the Schuylkill River Watershed and is almost completely surrounded by water: The Cobbs and Darby creeks to the west, the Delaware River and wetlands to the south, and the Schuylkill River and Mingo Creek to the east. The community is at continual risk of both riverine and coastal flooding, and faces an uncertain future due to sea level rise and riverine flooding exacerbated by climate change.
Princeton Hydro, along with project partners KeystoneConservation and University of Pennsylvania, conducted an analysis of Eastwick, the flood impacts created by the Lower Darby Creek, and the viability of several potential flood mitigation strategies.
Flood mitigation approaches can be structural and nonstructural. Structural mitigation techniques focus on reconstructing landscapes, including building floodwalls/seawalls and installing floodgates/levees. Nonstructural measures work to reduce damage by removing people and property out of risk areas, including zoning, elevating structures, and conducting property buyouts.
For Eastwick, studying stream dynamics is a key component to determining what type of flood mitigation strategies will yield the most success, as well as identifying the approaches that don’t work for this unique area.
Princeton Hydro’s study focused on the key problem areas in Eastwick: the confluence of Darby Creek and Cobbs Creek; a constriction at Hook Road and 84th Street; and the Clearview Landfill, which is part of the Lower Darby Creek Superfund site. Additionally, the study sought to answer questions commonly asked by community members related to flooding conditions, with the main question being: What impact does the landfill have on area flooding?
The built-up landfill is actually much higher than the stream bed, which creates a major disconnection between the floodplain and the stream channel. If the landfill didn’t exist, would the community still be at risk? If we increased the floodplain into the landfill, would that reduce neighborhood flooding?
Princeton Hydro set out to answer these questions by developing riverine flooding models primarily using data from US Army Corps of Engineers (USACE), Federal Emergency Management Agency (FEMA), The National Oceanic and Atmospheric Administration (NOAA), and NOAA's National Weather Service (NWS). FEMA looks at the impacts of 1% storms that are primarily caused by precipitation events as well as coastal storms and storm surge. NOAA looks at the impacts of hurricanes. And, NOAA's NWS estimates sea, lake and overland storm surge heights from hurricanes.
The models used 2D animation to show how the water flows in various scenarios, putting long-held assumptions to the test.
The models looked at several different strategies, including the complete removal of the Clearview Landfill, which many people anticipated would be the silver bullet to the area’s flooding. The modeling revealed, however, that those long-held assumptions were invalid. Although the landfill removal completely alters the flood dynamics, the neighborhood would still flood even if the landfill weren’t there. Additionally, the modeling showed that the landfill is actually acting as a levee for a large portion of the Eastwick community.
Ultimately, the research and modeling helped conclude that for the specific scenarios we studied, altering stream dynamics – a non-structural measure – is not a viable flood mitigation strategy.
The USACE is currently undergoing a study in collaboration with the Philadelphia Water Department to test the feasibility of a levee system (a structural control measure), which would protect the Eastwick community by diverting the flood water. Funding for the study is expected to be approved in the coming year.
There are many studies highlighting flood mitigation strategies, environmental justice, and climate change vulnerability in Eastwick. Princeton Hydro Senior Project Manager and Senior Ecologist, Christiana Pollack CFM, GISP, presented on the flooding in Eastwick at the Consortium for Climate Risk in the Urban Northeast Seminar held at Drexel University. The seminar also featured presentations from Michael Nairn of the University of Pennsylvania Urban Studies Department, Ashley DiCaro of Interface Studios, and Dr. Philip Orton of Stevens Institute of Technology.
For more information about Princeton Hydro’s flood management services, go here.
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.
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.
Sinkholes are a phenomenon that tend to baffle and frighten most people. How is it possible that the ground beneath our feet could just drop? How do we know if we’re nearby a sinkhole? What should we do if we see one? How are sinkholes fixed? The mystery of the unknown around sinkholes can be quite unnerving.
Have no fear, we’ve got answers to all of those questions and more! In this two-part blog series, our experts share their knowledge and provide important information about this scary occurrence. In part one, we provide a detailed look at what a sinkhole is, three different types of sinkholes, and what causes them to form. In part two, we explore how to detect sinkholes and the steps taken to repair them.
Sinkholes are a common phenomenon around the world. They result from both man-made and natural causes. Marshall Thomas, a Princeton Hydro geologist, describes sinkholes as “depressions observed from the surface, caused by dissolution of carbonate rocks.” In other words, sinkholes form when the rock below the land surface gets dissolved by water that penetrates the surface and continues to move downward, further into the subsurface.
Most common in areas with “karst terrain,” or types of rocks that can easily be dissolved by groundwater, sinkholes can go undetected for years until the space underneath the surface gets too big or enough of the surface soil is washed away. Sometimes the holes are small, measuring a few feet wide and ten feet deep. Sometimes the holes are hundreds of miles wide and deep. However, all of them can be dangerous.
Sinkholes are found throughout the world. States like Pennsylvania, Texas, Florida, Alabama, Tennessee, and Missouri are at higher risk for sinkholes because they tend to have more soluble rocks like salt beds and domes, gypsum, limestone, and other carbonate rocks. People living in these states are recommended to have professionals look at any property they intend to buy to make sure it isn’t in an area above soluble rock.
Not all sinkholes are the scary, earth-falling-out-from-underneath-your-feet events. Some occur slowly over time and are very evident from the surface. Geologists classify sinkholes in three major types. Their formation is determined by the same geological processes, barring a few differences. Let's dive in!
Dissolution sinkholes start to form when limestone or dolomite is very close to the soil surface, usually covered by a thin layer of soil and permeable sand which washes away or is eroded. Rain and stormwater runoff gradually percolate through crevices in the rock, dissolving it. Consequently, a bowl-shaped depression slowly forms.
Sometimes, dissolution sinkholes become ponds when the depression gets lined with debris, which traps water inside. Dissolution sinkholes develop gradually and are normally not dangerous. However, the ones that become ponds can drain abruptly if water breaks through the protective bottom layer.
2. Cover-Subsidence Sinkholes
This type of sinkhole, which starts with the dissolution of the underlying carbonate bedrock, occurs where the covering sediment is permeable (water can pass through it) and contains sand. First, small pieces of sediment split into smaller pieces and fall into openings in the carbonate rock underneath the surface. With time, in a process called piping, the small particles settle into the open spaces. This continues, eventually forming a dip in the surface ranging from one inch to several feet in depth and diameter. Again, these aren’t the sinkholes movies are made about.
3. Cover-Collapse Sinkholes
This type of sinkhole is the one making headlines and causing fear. In order for cover-collapse sinkholes to happen, the covering soil has to be cohesive, contain a lot of clay and the bedrock has to be carbonate. Similar to the cover-subsidence sinkholes, the cohesive soil erodes into a cavity in the bedrock. The difference with this is that the clay-filled top surface appears to remain intact from above. However, underneath, a hollowed out, upside down bowl shape forms. That hollowing gets bigger and bigger over time until eventually, the cavity reaches the ground surface, causing the sudden and dramatic collapse of the ground. Just like that, poof, we have a sinkhole that appears to be surprising and abrupt but really has been brewing for many years.
Sinkholes can be natural or man-made. The most common causes of a sinkhole are changes in groundwater levels or a sudden increase in surface water.
Intensive rain events can increase the likelihood of a sinkhole collapse. Alternatively, drought, which causes groundwater levels to significantly decrease, can also lead to a greater risk of collapse of the ground above. In a world with a greater variability in rainfall and drought events due to climate change, sinkholes may become a more common occurrence around the world.
Humans are also responsible for the formation of sinkholes. Activities like drilling, mining, construction, broken water or drain pipes, improperly compacted soil after excavation work, or even significantly heavy traffic (heavy weight on soft soil) can result in small to large sinkholes. Water from broken pipes can penetrate through mud and rocks and erode the ground underneath and cause sinkholes.
In some cases, human-induced sinkholes occur when an already forming sinkhole is encountered during construction processes such as excavation for stormwater basins and foundations. Dissolution of bedrock generally occurs in geologic time-frames (thousands of years). In these cases, the excavation process has removed the covering soils, decreasing the distance between the top of the void and the ground surface.
In other cases, voids in the bedrock are generated due to rock removal processes such as hammering and blasting. Hammering and blasting can generate fractures or cracks in the bedrock that soil can then erode into. A void in the bedrock may already exist, however, the process of removing the bedrock by hammering and/or blasting can speed up the meeting of the upside-down bowl and the surface that much quicker. One site where this happened has experienced over 35 sinkholes in 4 years.
Overall, it’s generally not a good idea to pump groundwater or do major excavation in areas that are prone to sinkholes. According to the USGS, over the last 15 years sinkhole damages have cost on average at least $300 million per year. Because there is no national tracking of sinkhole damage costs, this estimate is probably much lower than the actual cost. Being more mindful about the subsurface around us and our actions could help lower the average yearly cost in damages and even save lives.
Stay tuned for Part Two of this blog series in which we explore we explore how to detect sinkholes and the steps taken to repair them! For more information about Princeton Hydro’s Geotechnical Engineering services, click here.
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