Part One: Damned If You Do, Dammed If You Don’t: Making Decisions and Resolving Conflicts on Dam Removal

People have been building dams since prerecorded history for a wide variety of economically valuable purposes including water supply, flood control, and hydroelectric power. Back in the 1950s and 60s, the U.S. saw a boom in infrastructure development, and dams were being built with little regard to their impacts on rivers and the environment. By the 1970’s, the rapid progression of dam building in the U.S. led researchers to start investigating the ecological impacts of dams. Results from these early studies eventually fueled the start of proactive dam removal activities throughout the U.S.

Despite the proven benefits of dam removal, conflicts are a prevalent part of any dam removal project. Dam removal, like any other social decision-making process, brings up tensions around economics and the distribution of real and perceived gains and losses. In this two part blog series, we take a look at addressing and preventing potential conflicts and the key factors involved in dam removal decision-making – to remove or not to remove.

Why We Remove Dams

The primary reasons we remove dams are safety, economics, ecology, and regulatory. There has been a growing movement to remove dams where the costs – including environmental, safety, and socio-cultural impacts – outweigh the benefits of the dam or where the dam no longer serves any useful purpose. In some cases, it’s more beneficial economically to remove a dam than to keep it, even if it still produces revenue. Sometimes the estimated cost of inspection, repair, and maintenance can significantly exceed the cost of removal, rendering generated projected revenue insignificant.

Safety reasons are also vital, especially for cases in which dams are aging, yet still holding large amounts of water or impounded sediment. As dam’s age and decay, they can become public safety hazards, presenting a failure risk and flooding danger. 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.” Dam removal has increasingly become the best option for property owners who can no longer afford the rising cost of maintenance and repair work required to maintain these complex structures.

The goal of removal can be multi-faceted, including saving taxpayer money; restoring flows for migrating fish, other aquatic organisms, and wildlife; reinstating the natural sediment and nutrient flow; eliminating safety risks; and restoring opportunities for riverine recreation.

Moosup River

Common Obstacles to Dam Removal

Dam removal efforts are often subjected to a number of different obstacles that can postpone or even halt the process altogether. Reasons for retaining dams often involve: aesthetics and reservoir recreation; water intakes/diversions; hydroelectric; quantity/quality of sediment; funding issues; cultural/historic values of manmade structures; owner buy-in; sensitive species; and community politics.

Of those common restoration obstacles, one of the more frequently encountered challenges is cost and funding. Determining who pays for the removal of a dam is often a complex issue. Sometimes, removal can be financed by the dam owner, local, state, and federal governments, and in some cases agreements are made whereby multiple stakeholders contribute to cover the costs. Funding for dam removal projects can be difficult to obtain because it typically has to come from a variety of sources.

Anecdotally, opposition also stems from fear of change and fear of the unknown. Bruce Babbitt, the United States Secretary of the Interior from 1993 through 2001 and dam removal advocate, said in an article he wrote, titled A River Runs Against It: America’s Evolving View of Dams, “I always wonder what is it about the sound of a sledgehammer on concrete that evokes such a reaction? We routinely demolish buildings that have served their purpose or when there is a better use for the land. Why not dams? For whatever reason, we view dams as akin to the pyramids of Egypt—a permanent part of the landscape, timeless monuments to our civilization and technology.”

Negative public perceptions of dam removal and its consequences can seriously impede removal projects. Although there are many reasons for the resistance to dam removal, it is important that each be understood and addressed in order to find solutions that fulfill both the needs of the environment and the local communities.

Stay tuned for Part Two of this blog series in which we explore strategies for analyzing dams and what goes into deciding if a dam should remain or be removed.

Study Data Leads to Healthier Wreck Pond Ecosystem

Wreck Pond is a tidal pond located on the coast of the Atlantic Ocean in southern Monmouth County, New Jersey. The 73-acre pond, which was originally connected to the sea by a small and shifting inlet, got its name in the 1800s due to the numerous shipwrecks that occurred at the mouth of the inlet. The Sea Girt Lighthouse was built to prevent such accidents. In the 1930s, the inlet was filled in and an outfall pipe was installed, thus creating Wreck Pond. The outfall pipe allowed limited tidal exchange between Wreck Pond and the Atlantic Ocean.

In the 1960s, Wreck Pond flourished with wildlife and was a popular destination for recreational activities with tourists coming to the area mainly from New York City and western New Jersey. In the early spring, hundreds of river herring would migrate into Wreck Pond, travelling up its tributaries — Wreck Pond Brook, Hurleys Pond Brook and Hannabrand Brook — to spawn. During the summer, the pond was bustling with recreational activities like swimming, fishing, and sailing.

Over time, however, the combination of restricted tidal flow and pollution, attributable to increased development of the watershed, led to a number of environmental issues within the watershed, including impaired water quality, reduced fish populations, and flooding.

Throughout the Wreck Pond watershed, high stream velocities during flood conditions have caused the destabilization and erosion of stream banks, which has resulted in the loss of riparian vegetation and filling of wetlands. Discharge from Wreck Pond during heavy rains conveys nonpoint source pollutants that negatively impact nearby Spring Lake and Sea Girt beaches resulting in beach closings due to elevated bacteria counts. Watershed erosion and sediment transported with stormwater runoff has also contributed to excessive amounts of sedimentation and accumulations of settled sediment, not only within Wreck Pond, but at the outfall pipe as well. This sediment further impeded tidal flushing and the passage of anadromous fish into and out of Wreck Pond.

In 2012, Hurricane Sandy caused wide-spread destruction throughout New Jersey and the entire eastern seaboard. The storm event also caused a major breach of the Wreck Pond watershed’s dune beach system and failure of the outfall pipe. The breach formed a natural inlet next to the outfall pipe, recreating the connection to the Atlantic Ocean that once existed. This was the first time the inlet had been open since the 1930s, and the reopening cast a new light on the benefits of additional flow between the pond and the ocean.

Hurricane Sandy sparked a renewed interest in reducing flooding impacts throughout the watershed, including efforts to restore the water quality and ecology of Wreck Pond. The breach caused by Hurricane Sandy was not stable, and the inlet began to rapidly close due to the deposition of beach sand and the discharge of sediment from Wreck Pond and its watershed.

Princeton Hydro and HDR generated the data used to support the goals of the feasibility study through a USACE-approved model of Wreck Pond that examined the dynamics of Wreck Pond along with the water bodies directly upland, the watershed, and the offshore waters in the immediate vicinity of the ocean outfall. The model was calibrated and verified using available “normalized” tide data. Neighboring Deal Lake, which is also tidally connected to the ocean by a similar outfall pipe, was used as the “reference” waterbody. The Wreck Pond System model evaluated the hydraulic characteristics of Wreck Pond with and without the modified outfall pipe, computed pollutant inputs from the surrounding watershed, and predicted Wreck Pond’s water quality and ecological response. The calibrated model was also used to investigate the effects and longevity of dredging and other waterway feature modifications.

As part of the study, Princeton Hydro and HDR completed hazardous, toxic, and radioactive waste (HTRW) and geotechnical investigations of Wreck Pond’s sediment to assess potential flood damage reduction and ecological restoration efforts of the waterbody. The investigation included the progression of 10 sediment borings conducted within the main body of Wreck Pond, as well as primary tributaries to the pond. The borings, conducted under the supervision of our geotechnical staff, were progressed through the surgical accumulated sediment, not the underlying parent material. Samples were collected for analysis by Princeton Hydro’s AMRL-accredited (AASHTO Materials Reference Library) and USACE-certified laboratory. In accordance with NJDEP requirements, sediment samples were also forwarded to a subcontracted analytical laboratory for analysis of potential nonpoint source pollutants.

In the geotechnical laboratory, the samples were subjected to geotechnical indexing tests, including grain size, organic content, moisture content, and plasticity/liquid limits. For soil strength parameters, the in-field Standard Penetration Test (SPT), as well as laboratory unconfined compression tests, were performed on a clay sample to provide parameters for slope stability modeling.

The culvert construction and sediment dredging were completed at the end of 2016. Continued restoration efforts, informed and directed by the data developed through Princeton Hydro’s feasibility study, are helping to reduce the risk of flooding to surrounding Wreck Pond communities, increase connectivity between the pond and ocean, and improve water quality. The overall result is a healthier, more diverse, and more resilient Wreck Pond ecosystem.

During the time of the progression of study by the USACE, the American Littoral Society and the towns of Spring Lake and Sea Girt were also progressing their own restoration effort and completed the implementation of an additional culvert to the Atlantic Ocean.  The American Littoral Society was able to utilize the data, analysis, and modeling results developed by the USACE to ensure the additional culvert would increase tidal flushing and look to future restoration projects within Wreck Pond.

American Littoral Society

 

To learn more about our geotechnical engineering services, click here.

Part Two: Reducing Flood Risk in Moodna Creek Watershed

Photo of Moodna Creek taken from the Forge Hill Road bridge, New Windsor Post Hurricane Irene (Courtesy of Daniel Case via Wikimedia Commons)

This two-part blog series showcases our work in the Moodna Creek Watershed in order to explore common methodologies used to estimate flood risk, develop a flood management strategy, and reduce flooding.

Welcome to Part Two: Flood Risk Reduction and Stormwater Management in the Moodna Creek Watershed

As we laid out in Part One of this blog series, the Moodna Creek Watershed, which covers 180 square miles of eastern Orange County, New York, has seen population growth in recent years and has experienced significant flooding from extreme weather events like Hurricane Irene, Tropical Storm Lee, and Hurricane Sandy. Reports indicate that the Moodna Creek Watershed’s flood risk will likely increase as time passes.

Understanding the existing and anticipated conditions for flooding within a watershed is a critical step to reducing risk. Our analysis revealed that flood risk in the Lower Moodna is predominantly driven by high-velocity flows that cause erosion, scouring, and damage to in-stream structures. The second cause of risk is back-flooding due to naturally formed and man-made constrictions within the channel. Other factors that have influenced flood risk within the watershed, include development within the floodplain and poor stormwater management.

Now, let’s take a closer look at a few of the strategies that we recommended for the Lower Moodna Watershed to address these issues and reduce current and future flood risk:

Stormwater Management

Damage to Butternut Drive caused when Moodna Creek flooded after Hurricane Irene (Courtesy of Daniel Case via Wikimedia Commons)

Stormwater is the runoff or excess water caused by precipitation such as rainwater or snowmelt. In urban areas, it flows over sewer gates which often drain into a lake or river. In natural landscapes, plants absorb and utilize stormwater, with the excess draining into local waterways.  In developed areas, like the Moodna Creek watershed, challenges arise from high volumes of uncontrolled stormwater runoff. The result is more water in streams and rivers in a shorter amount of time, producing higher peak flows and contributing to flooding issues.

Pollutant loading is also a major issue with uncontrolled stormwater runoff. Population growth and development are major contributors to the amount of pollutants in runoff as well as the volume and rate of runoff. Together, they can cause changes in hydrology and water quality that result in habitat loss, increased flooding, decreased aquatic biological diversity, and increased sedimentation and erosion.

To reduce flood hazards within the watershed, stormwater management is a primary focus and critical first step of the Moodna Creek Watershed Management Plan. The recommended stormwater improvement strategies include:

  • Minimizing the amount of impervious area within the watershed for new development, and replacing existing impervious surfaces with planter boxes, rain gardens and porous pavement.
  • Utilizing low-impact design measures like bioretention basins and constructed-wetland systems that mimic the role of natural wetlands by temporarily detaining and filtering stormwater.
  • Ensuring the long-term protection and viability of the watershed’s natural wetlands.

The project team recommended that stormwater management be required for all projects and that building regulations ensure development does not change the quantity, quality, or timing of run-off from any parcel within the watershed. Recommendations also stressed the importance of stormwater management ordinances focusing on future flood risk as well as addressing the existing flooding issues.

Floodplain Storage

Floodplains are the low-lying areas of land where floodwater periodically spreads when a river or stream overtops its banks. The floodplain provides a valuable function by storing floodwaters, buffering the effect of peak runoff, lessening erosion, and capturing nutrient-laden sediment.

Communities, like the Moodna Creek watershed, can reduce flooding by rehabilitating water conveyance channels to slow down the flow, increasing floodplain storage in order to intercept rainwater closer to where it falls, and creating floodplain benches to store flood water conveyed in the channel.  Increasing floodplain storage can be an approach that mimics and enhances the natural functions of the system.

One of the major causes of flooding along the Lower Moodna was the channel’s inability to maintain and hold high volumes of water caused by rain events. During a significant rain event, the Lower Moodna channel tends to swell, and water spills over its banks and into the community causing flooding. One way to resolve this issue is by changing the grading and increasing the size and depth of the floodplain in certain areas to safely store and infiltrate floodwater. The project team identified several additional opportunities to increase floodplain storage throughout the watershed.

One of the primary areas of opportunity was the Storm King Golf Club project site (above). The team analyzed the topography of the golf course to see if directing flow onto the greens would alter the extent and reach of the floodplain thus reducing the potential for flooding along the roadways and properties in the adjacent neighborhoods. Based on LiDAR data, it was estimated that the alteration of 27 acres could increase floodplain storage by 130.5 acre-feet, which is equivalent to approximately 42.5 million gallons per event.

Land Preservation & Critical Environmental Area Designation

For areas where land preservation is not a financially viable option, but the land is undeveloped, prone to flooding, and offers ecological value that would be impacted by development, the project team recommended a potential Critical Environmental Area (CEA) designation. A CEA designation does not protect land in perpetuity from development, but would trigger environmental reviews for proposed development under the NY State Quality Environmental Review Act. And, the designation provides an additional layer of scrutiny on projects to ensure they will not exacerbate flooding within the watershed or result in an unintentional increase in risk to existing properties and infrastructure.

Conserved riparian areas also generate a range of ecosystem services, in addition to the hazard mitigation benefits they provide. Protected forests, wetlands, and grasslands along rivers and streams can improve water quality, provide habitat to many species, and offer a wide range of recreational opportunities. Given the co-benefits that protected lands provide, there is growing interest in floodplain conservation as a flood damage reduction strategy.


These are just a few of the flood risk reduction strategies we recommended for the Lower Moodna Creek watershed. For a more in-depth look at the proposed flood mitigation strategies and techniques, download a free copy of our Moodna Creek Watershed and Flood Mitigation Assessment presentation.

Revisit part-one of this blog series, which explores some of the concepts and methods used to estimate flood risk for existing conditions in the year 2050 and develop a flood management strategy.

Two-Part Blog Series: Flood Assessment, Mitigation & Management

For more information about Princeton Hydro’s flood management services, go here: http://bit.ly/PHfloodplain

Conservation Spotlight: Reducing Flood Risk and Restoring Wetlands in Jamaica Bay

Located in Queens, New York on the northern shore of Jamaica Bay, Spring Creek South contains approximately 237 acres of undeveloped land, including wetlands and 2.4 miles of coastline. The site is bounded by the Howard Beach residential neighborhood in Queens, a commercial area along Cross Bay Boulevard, the Belt Parkway, and Jamaica Bay. The northwest section of Spring Creek South is part of the National Park Service’s Gateway National Recreation Area, and is largely comprised of small patches of degraded tidal marsh and disturbed and degraded upland ecosystems.

On October 29, 2012, Hurricane Sandy drove a catastrophic storm surge into the New Jersey and New York coastlines. Spring Creek South and the surrounding community of Howard Beach experienced record flooding and damage to property and critical infrastructure. Storm tides caused damage and erosion along the shoreline and in the salt marsh area, degrading important habitat and leaving the site vulnerable to invasive species.

Hurricane Sandy Aftermath at Howard Beach, taken 10/30/2012 by Pam Andrade

The New York State Division of Homeland Security and Emergency Services (NYSDHSES) was awarded funding from FEMA’s Hazard Mitigation Grant Program to restore Spring Creek South. The U.S. Army Corps of Engineers (USACE) New York District, serving as project administrator, contracted Princeton Hydro to provide ecosystem restoration services. The goal of the project is to reduce future flood risk exposure while also protecting, restoring, and improving the quality and function of ecological systems; improving stormwater management and water quality; and enhancing the park’s visitor experience.

To achieve this goal, the project team is using an integrated approach that involves utilizing green infrastructure to create a natural barrier for the community and reduce the risks of coastal storms. Project activities include berm construction and the restoration of tidal marsh, creation of freshwater wetland forest, and creation of maritime shrub, forest, and grassland habitats, as well as stabilization of the existing shoreline.

On December 31, 2018, we completed Phase One of the project, which entails engineering design and preliminary permitting. More specifically, we’ve provided conceptual planning; analysis of subsurface soils for geotechnical properties and hazardous waste; coastal and freshwater wetland delineations; biological benchmarking analysis; and the development of sea level rise curves and two-dimensional hydrologic and hydraulic coastal modeling. As part of the hydrology study, we analyzed what the site could be expected to look like in 50 years due to climate changes and sea level rise. Our engineering design was also brought to 65% completion.

We also obtained permits, prepared the Environmental Assessment (EA), and oversaw the National Environmental Policy Act (NEPA) process. The EA received a “Finding of No Significant Impact” (FONSI) from FEMA, which means the environmental analysis and interagency review concluded that the project has no significant impacts on the quality of the environment.

Due to the complex nature of this project and its location, we are coordinating with a variety of different entities, including the local Howard Beach Community Board, the FAA (proximity to JFK International Airport), Port Authority, USACE, NOAA Fisheries, USFWS, USEPA, NYSDEC, NYC DEP, the National Park Service, HDR Engineering and WSP Engineering.

Phase Two of the project is the construction phase, which is expected to take about two years to complete. A key part of the Spring Creek South construction activities is the restoration of approximately 40 acres of tidal marsh, which is anticipated to improve water quality locally by stabilizing sediment, reducing erosion, and filtering dissolved particulate materials. The project team will restore existing coastline areas and install a salt marsh along the shoreline. Planted with native flora, like Spartina alterniflora, a perennial deciduous grass found in intertidal wetlands, the coastal salt marsh will help to stabilize sediment. Additionally, removing invasive species like Phragmites australis from the area and replacing it with native plant species will increase the ability for native vegetation to colonize the site, improve vegetative diversity, and reduce fire risk in the park.

A forested wetland area and berm will also be created in order to provide the surrounding communities with natural shields and buffers to future storms. The berm, with an elevation of 19 feet (NAVD88), will help to manage the risk of storm surge flooding caused by coastal storms. The forested wetland area will also provide improved stormwater runoff storage, naturally filter stormwater, and, via flap gates, direct its flow toward Jamaica Bay, away from residential and commercial properties.

These measures will help to dissipate wind and wave energy, increase shoreline resilience, improve stormwater management at the site, and create habitat that increases the ecological value and biodiversity at the site, while providing resilience benefits. Restoration activities will benefit vulnerable and rare ecological communities by producing localized environmental enhancements, including improving water quality and creating and restoring habitat. The project also increases opportunities for recreational uses such as wildlife viewing/photography, fishing, and nature study.

Princeton Hydro specializes in the planning, design, permitting, implementing, and maintenance of wetland rehabilitation projects. To learn more about some of our ecosystem restoration and enhancement services, visit: bit.ly/PHwetland.

 

Levee Inspections Along the Elizabeth River

Ursino Dam on the Elizabeth River in Union County, New Jersey is one of the sites Princeton Hydro inspected for flood control, ensuring the system is providing the level of protection it was designed to deliver.

By Brendon Achey, Princeton Hydro’s Lead Geologist; Soils Laboratory Manager; Project Manager

Located 20 miles southwest of New York City, the City of Elizabeth, New Jersey, is situated along the Elizabeth River. For the city’s 125,000 residents, living along the river has many benefits, but the benefits are not without flood risk. In order to manage the risk associated with potential flooding, a series of levees and floodwalls were installed along the banks of the Elizabeth River. A levee is an embankment that is constructed to prevent overflow from a river. They are a crucial element for protecting cities from disastrous flooding, and as such they require periodic inspections to ensure that all components are functioning properly.

Princeton Hydro was contracted by the U.S. Army Corps of Engineers, New York District (USACE NYD) to perform rigorous flood control project inspections (i.e., “Periodic Inspections”) for the four levee systems located along the Elizabeth River.  For this project, our team inspected over 17,000 linear feet of levee embankment and 2,500 linear feet of floodwall.

Levee systems are comprised of components which collectively provide flood risk management to a defined area. These components can include levees, structural floodwalls, closure gates, pumping stations, culverts, and interior drainage works. These components are interconnected and collectively ensure the protection of development and/or infrastructure that is situated within a floodplain. Failure of just one critical component within a system could constitute an overall system failure. During Hurricane Katrina, for example, dozens of levees were destroyed, leaving the Louisiana coast with billions of dollars in damage and over one thousand lives lost.

Periodic inspections are necessary in order to ensure a levee system will perform as expected. They are also needed to identify deficiencies in the levee, or areas that need monitoring or immediate repair. Critically important maintenance activities include continuously assessing the integrity of the levee system to identify changes over time, collecting information to help inform decisions about future actions, and providing the public with information about the levees on which they rely.

Levee Inspection Process

Periodic inspections are extremely comprehensive and include three key steps: data collection, field inspection, and development of a final report.

Data Collection

Prior to conducting field inspections, Princeton Hydro’s engineers evaluated the Elizabeth River levee system’s documented design criteria. This evaluation was conducted to assess the ability of each feature and the overall system to function as authorized, and also to identify any potential need to update the system design. Princeton Hydro teamed with HDR to carry out the inspections. A comprehensive review of existing data on operation and maintenance, previous inspections, emergency action plans, and flood fighting records was also performed.

Field Inspection

The Princeton Hydro field inspection team consisted of geotechnical, water resource, mechanical, structural, and electrical engineers. Detailed inspections were performed on each segment of each levee system.  This included the detailed inspection and documentation of over 17,000 linear feet of levee embankment, over 2,500 linear feet of floodwall, four pumping stations, 29 interior drainage structures, five closure gates, and various other encroachments and facilities. Princeton Hydro identified, evaluated, and rated the state of each of these system elements. As part of this field inspection task, Princeton Hydro utilized a state-of-the-art tablet and GIS technology in order to field-locate inspection points and record item ratings. This digital collection of data helps expedite data processing and ensures higher levels of accuracy.

Development of Final Report

Princeton Hydro prepared a Periodic Inspection Report for each of the four levee systems inspected, which included the results of the design document review, methods and results of the field inspection, a summary of areas/items of concern, a preliminary engineering assessment of causes of distress or abnormal conditions, and recommendations for remedial actions to address identified concerns. Final report development included briefing the USACE Levee Safety Officer (LSO) on our inspection findings, assigned ratings, and recommendations.

Levee inspections are vital to the longevity of levee systems and the safety of the communities they protect. By providing the municipalities with detailed inspection reports, effective repair and management programs can be designed and implemented efficiently. This helps to ensure the levee systems are providing the level of protection that they were designed to deliver.

Princeton Hydro’s Geoscience and Water Resource Engineering teams perform levee and dam inspections throughout the Mid-Atlantic and New England Regions. For more info, visit: http://bit.ly/PHEngineering

Brendon Achey provides a wide range of technical skills and services for Princeton Hydro. His responsibilities include: project management, preparation and quality control of technical deliverables, geotechnical investigations and analysis, groundwater hydrology, soil sampling plan design and implementation, and site characterization. He is responsible for managing the daily operations of the AASHTO accredited and USACE validated soil testing laboratory. In addition to laboratory testing and analysis, Brendon is responsible for analyzing results in support of geotechnical and stormwater management design evaluations. This may include bearing capacity and settlement analysis of both shallow and deep foundations, retaining wall design, and recommendations for stormwater management practices.

Two-Part Blog Series: Flood Assessment, Mitigation & Management

In this two part blog series, we showcase our work in the Moodna Creek Watershed in order to explore some of the concepts and methods used to estimate flood risk for existing conditions and the year 2050 and develop a flood management strategy (Part One), and traditional engineering and natural systems solutions used to manage and reduce flood risk (Part Two).

Part One: Flood Assessment & Mitigation Analysis in the Moodna Creek Watershed

The greater Moodna Creek watershed covers 180 square miles of eastern Orange County, NY. The watershed includes 22 municipalities and hundreds of streams before joining the Hudson River. This region has seen tremendous growth in recent years with the expansion of regional transit networks and critical infrastructure.

The Moodna Creek watershed can be split into two sub-basins — the Upper Moodna Creek and the Lower Moodna Creek. In the span of 15 months, Hurricane Irene, Tropical Storm Lee, and Hurricane Sandy each have caused significant flooding throughout the Moodna Creek watershed, damaging public facilities, roadways, and private properties. Both sub-basin communities have noted a concern about increased flood risk as more development occurs.

As global temperatures rise, climate models are predicting more intense rainfall events. And, the flood risk for communities along waterways — like the Moodna Creek watershed — will likely increase as time passes. In order to understand existing and future risk from flood events in this flood-prone area, a flood risk management strategy needed to be developed. The strategy uses a cost-benefit analysis to review the feasibility of each measure and the overall impact in reducing flood risks.

With funds provided from a 2016 grant program sponsored by the New England Interstate Waters Pollution Control Commission (NEIWPCC) and the New York State Department of Environmental Conservation’s (NYCDEC) Hudson River Estuary Program (HEP), Princeton Hydro along with a variety of project partners completed a flood assessment and flood mitigation analysis specific to the Lower Moodna Creek watershed.

Let’s take a closer look at our work with the Lower Moodna Creek watershed, and explore some of the methods used to estimate flood risk and develop a flood management strategy:

Lower Moodna Creek Watershed Flood Assessment & Analysis

The primary Lower Moodna Creek project goals were to assess flood vulnerabilities and propose flood mitigation solutions that consider both traditional engineering strategies and natural systems solution approaches (land preservation, wetland/forest restoration, green infrastructure and green water management). The project team focused on ways to use the natural environment to reduce risk.  Instead of strictly focusing on just Moonda Creek, the team took a holistic approach which included all areas that drain into the river too. These analyses were incorporated into a Flood Assessment Master Plan and Flood Mitigation Plan, which will serve as a road map to reducing flooding issues within the watershed.

Managing Flood Risk

The first step in managing flood risk is to understand what type of exposure the communities face. The Moodna Creek project modeled flooding within the watershed during normal rain events, extreme rain events, and future rain events with two primary goals in mind:

Visual assessment being conducted in flood-prone areas of Moodna Creek Watershed.

  • Assess the facilities, infrastructure, and urban development that are at risk from flooding along the Moodna Creek and its tributaries within the study area.
  • Develop a series of hydrologic and hydraulic models to assess the extent of potential flooding from the 10-year (10%), 100-year (1%),  and 500-year (0.2%) storm recurrence intervals within the study area. The modeling includes flows for these storm events under existing conditions and also hypothetical scenarios with predicted increases in precipitation and population growth.

 

The project team used these models and data to propose and evaluate a series of design measures that help reduce and mitigate existing and anticipated flood risk within the study area. Where possible, the proposed solutions prioritized approaches that protect and/or mirror natural flood protection mechanisms within the watershed such as floodplain re-connection and wetland establishment. In addition to flood protection, the project components also provide water quality protection, aesthetics and recreation, pollutant reduction, and wildlife habitat creation.

Land Use and Zoning

Zoning is a powerful tool that determines a region’s exposure to hazards and risk. Zoning determines which uses are permitted, or encouraged, to be built in moderate and high-risk areas. It also prevents certain uses, such as critical facilities, from being built in those areas. Zoning is also a determinant of a region’s character and identity.

In the Lower Moodna Creek watershed, a large majority (82%) of land is zoned for residential use. However, in the flood-prone areas, there is a higher ratio of areas zoned for non-residential uses (commercial, industrial) than in areas that are zoned for potential future development. Specifically, within the 10-year storm recurrence floodplain, 30% of the land is zoned for industrial use. This is likely because several facilities, such as wastewater treatment plants and mills, require access to the river and were strategically developed to be within immediate proximity of waterfront access. The Lower Moodna zoning analysis demonstrated a general preference within watershed to limit residential use of flood-prone areas. 

Land Preservation

Preserving land allows for natural stormwater management, as well as limits the exposure of development, and minimizes sources of erosion within the watershed. Preserved land also maintains the hydrologic and ecologic function of the land by allowing rainwater to be absorbed or retained where it falls and thus minimizing run-off. If the land within the floodplain is preserved, it will never be developed, and therefore the risk — a calculation of rate exposure and the value of the potential damage — is eliminated.  Therefore, land preservation, both within the floodplains and in upland areas, is the best way to minimize flood damage.

Conserved riparian areas also generate a range of ecosystem services, in addition to the hazard mitigation benefits they provide. Protected forests, grasslands, and wetlands along rivers and streams can improve water quality, provide habitat to many species, and offer a wide range of recreational opportunities. Given the co-benefits that protected lands provide, there is growing interest in floodplain conservation as a flood damage reduction strategy.

Within the mapped Lower Moodna floodplains, our assessment determined that there appears to be a slight priority for preserving land most at-risk for flooding. This is likely a consequence of prioritizing land that is closest to riparian areas and preserving wetland areas, which are the most likely to experience flooding. Within the floodplains for the 10-year storm, approximately 22.7% is preserved. For the 100-year storm, approximately 21.2% of the land is preserved. Within the 500-year storm, this number drops slightly to 20.3%. These numbers are so close in part because the difference between the 10-year, 100-year, and 500-year floodplains are small in many areas of the watershed.

Hydrology and Hydraulics

Hydrology is the scientific study of the waters of the earth, with a particular focus on how rainfall and evaporation affect the flow of water in streams and storm drains. Hydraulics is the engineering analysis of the flow of water in channels, pipelines, and other hydraulic structures. Hydrology and hydraulics analyses are a key part of flood management.

As part of this flood assessment, Princeton Hydro created a series of hydrologic and hydraulic (H&H) models to assess the extent of potential flooding from the 10-year, 100-year, and 500-year storm recurrence intervals within the Lower Moodna. The modeling, which included flows for these storm events under existing conditions and future conditions based on predicted increases in precipitation and population growth, makes it easier to assess what new areas are most impacted in the future.

These are just a few of the assessments we conducted to analyze the ways in which flooding within the watershed may be affected by changes in land use, precipitation, and mitigation efforts. The flood models we developed informed our recommendations and proposed flood mitigation solutions for reducing and mitigating existing and anticipated flood risk.

Check out Part Two of this blog series in which we explore flood risk-reduction strategies that include both traditional engineering and natural systems solutions:

Part Two: Reducing Flood Risk in Moodna Creek Watershed

For more information about Princeton Hydro’s flood management services, go here: http://bit.ly/PHfloodplain.

 

Employee Spotlight: Meet Our New Team Members

We’re excited to welcome two new staff members and seven new part-time staff & interns to our team who are spread throughout our Ringoes, Sicklerville, and Glastonbury offices.

 

Full-Time Staff Members:
Kelsey Mattison, Marketing Coordinator

Kelsey is a recent graduate of St. Lawrence University with a degree in English and environmental studies and a passion for environmental communication. Through her extracurricular work with various nonprofit organizations, she has developed expertise in social media management, content writing, storytelling, and interdisciplinary thinking. Kelsey believes that effective communication needs to be multi-faceted, which is reflected in the diversity of her experience. She served as Photography Editor of St. Lawrence University’s newspaper, worked in digital media for the environmental outreach program of St. Lawrence University,  produced stories for Northern New York’s public radio station, and developed feature content for St. Lawrence County’s Chamber of Commerce. As a member of the Princeton Hydro team, she aims to further its mission by taking creative approaches to communicating about our shared home: Planet Earth. In her free time, Kelsey enjoys dancing of all sorts, going on long walks with her camera, and spending time with friends and family in nature.

Christine Worthington, Accounting Assistant

Christine is a detailed-oriented Accounting Assistant who has over 15 years of experience working in office administration for local businesses. She loves vacationing in Jamaica with her husband and spending time with her two sons & three grandchildren. In her free time, she listens to country music and visits new cities like Nashville.

 

Part-time Staff, Field Assistants & Interns:
Heidi Golden, PhD, Aquatic Ecologist

Heidi is an aquatic ecologist and evolutionary biologist with a strong background in fish monitoring, aquatic habitat assessment, population and community ecology, and population genetics and genomics. She holds a PhD in Ecology and Evolutionary Biology and a Master of Science in Forestry and Wildlife Biology. In addition to her ecology expertise, Heidi has experience in GIS analysis, R statistical programing, scientific writing, permitting, and a wide range of field and laboratory techniques. Prior to joining Princeton Hydro, Heidi worked as a postdoctoral researcher with The Woods Hole Research Center, The Marine Biological Laboratory, and The University of Connecticut, where she continues to serve as adjunct faculty to the Department of Ecology and Evolutionary Biology. She investigated ecological and evolutionary responses of fish populations to rapid environmental change. Her professional experience also includes coordinating field expeditions in remote locations of the Alaskan Arctic, tagging and tracking thousands of fish through remote PIT-tag antenna arrays, using environmental DNA to monitor fish presence and movement, and developing experiments to assess ecosystem responses to change. She enjoys raising ducks, swimming in cold rivers, hiking, kayaking, camping, and family.

Andrew Greenlaw, Water Resources Intern

Andrew Greenlaw is in his fourth year at the University of Connecticut, majoring in Civil Engineering with a minor in Environmental Engineering. Before studying engineering he taught at a Marine science summer camp in Groton, CT, off of the Long Island Sound. He joined Princeton Hydro with the hope of combining his biological sciences experience with his academic engineering knowledge. He enjoys hiking, fishing, and just about any outdoor sport.

Ryan Lindsay, Water Resources Intern

Ryan is a double major at Rowan University focusing in both Civil & Environmental Engineering and Computer Science, and is currently finishing his final semester. He’s worked on various engineering clinic projects ranging from developing a pavement analysis program for Rhode Island DOT to a feasibility study to assist those with disabilities. His current project is to develop a home security/monitoring system with an accompanying mobile application. In the future, Ryan hopes to develop civil engineering applications for use by design engineers, and hopes that with his unique skillset he can make future engineers’ jobs easier and more efficient. Ryan enjoys playing baseball, listening to music, hiking and hanging out with friends and family.

Nick Niezgoda, Aquatics Field Assistant

Nick graduated in 2017 from Western State Colorado University with a B.S. in Biology. He lived and worked at Rocky Mountain Biological Laboratory studying defense genotypes of B.stricta under Duke University’s Tom Mitchell-Olds Lab in 2016 and 2018. At RMBL, He also assisted in trapping and banding of Mountain White-Crowned Sparrows. He enjoys cycling, hiking, and birding!

Emily McGuckin, Aquatics Field Assistant

Emily is a recent graduate from Stockton University, with a BS in marine biology, and a minor in environmental science. She just finished up an internship with the American Littoral Society at Sandy Hook, where she helped manage the fish tagging program and educating others on the importance of maintaining an accurate fisheries database. She has experience in both freshwater and marine ecosystem management and is excited to continue learning about ecological restoration and management.  She is very interested in ecosystem resilience, specifically climate change and how it affects estuaries and estuarine organisms. Emily is hoping to attend graduate school in the near future to further her studies in marine science.

Pat Rose, Aquatics Field Assistant

Pat got interested in aquatics during a summer course studying at Lake Atitlán, Guatemala as an undergraduate at SUNY Oneonta. After graduation, he spent a year volunteering with AmeriCorps in Knoxville, TN as part of a Water Quality Team. While in Tennessee, he spent the majority of his time educating high school students on how to protect and improve local waterways and watersheds as part of the Adopt-A-Watershed program. The year, through AmeriCorps, he also worked with government organizations performing biological sampling and erosion monitoring in local streams. Pat is set to graduate from SUNY Oneonta with a M.S. in Lake Management in December. He created an interim lake management plan for a small reservoir in New York that has had cyanobacterial blooms over the past few years. Pat spent this past summer completing a co-op with an aquatic plant management company in the Pacific Northwest, working primarily with invasive Eurasian and hybrid watermilfoil populations.

 

October Events Spotlight: Conferences, Workshops & Galas

Throughout October, Princeton Hydro is proud to participate in a number of conferences and events on topics ranging from floodplain management to ecological restoration to dam removal:

October 10: Society for American Military Engineers (SAME) MEGA Maryland Small Business Conference

The conference, being held in Baltimore, gives small and minority businesses in the architecture, engineering and construction industries the opportunity to come together with federal agencies in order to showcase best practices and highlight future opportunities to work in the federal market. The program consists of networking events, a variety of speakers and small business exhibits. Be sure to stop by the Princeton Hydro booth to say hello to President Geoffrey Goll, P.E. and Communications Strategist Dana Patterson.

LEARN MORE & REGISTER

 

October 11: Great Swamp Gala & Silent Auction

The Great Swamp Watershed Association, a nonprofit organization dedicated to protecting and improving the water resources of the Passaic River region, is hosting its 2018 Gala & Silent Auction. This year’s event is being, held in honor of former New Jersey Governor Thomas Kean, for his environmental leadership during his administration for enacting landmark protections for New Jersey’s shoreline and freshwater wetlands. present and future generations. The evening will include a cocktail hour, dinner banquet, expansive silent auction, and remarks delivered by Governor Kean. Princeton Hydro is proud to be a Benefactor of the event and looking forward to attending.

LEARN MORE & REGISTER

 

October 11 – 13: Atlantic Estuarine Research Society (AERS) Fall Meeting

The theme of this year’s AERS Fall Meeting is “The power of framing your message: It’s not what you say, it’s how you say it!” Participants will gather at Stockton University to hear a variety of ignite-style presentations about misconceptions that typically surround scientific work, how to address them, and how to re-frame your message to be better understood by the general public and other non-scientists and increase stakeholder involvement. Princeton Hydro’s Senior Aquatics Scientist Jack Szczepanski, PhD will be attending the conference; chat with him to learn more about our pond and lake services.

LEARN MORE

 

October 11 – 13: Society for Ecological Restoration (SER) New England 2018 Regional Conference

This year’s SER New England conference brings together stewards, researchers, students, regulators, community activists and practitioners to explore innovative ecological restoration techniques and projects that connect communities within and across ecosystems. The conference includes a variety of plenary talks, field trips, workshops and a keynote address, which will be given by Stewart Diemont of SUNY College of Environmental Science and Forestry. The keynote, titled “Learning from the People and the Land: Traditional Ecological Knowledge Toward Restoration of Ecosystems and of our Connection with Nature,” is free and open to the public.

Members of the Princeton Hydro are attending the conference and leading two sessions: Laura Wildman, Water Resources and Fisheries Engineer, is leading a workshop about implementing dam removal to restore rivers. Paul Woodworth, Fluvial Geomorphologist, is presenting on the post-dam removal monitoring of active and passive restoration approaches utilizing the Hyde Pond Dam removal as a tangible example.

LEARN MORE & REGISTER

 

October 11: Hudson-Delaware Chapter of the Society of Environmental Toxicology and Chemistry (HDC-SETAC) 2018 Fall Workshop

HDC-SETAC is a professional society for scientists, engineers and related disciplines concerned with environmental science and health throughout the Hudson River and Delaware River metropolitan area. The 2018 Fall Workshop, being held at Villanova University, aims to enhance participants’ knowledge of “Harmful Algal Blooms and other Emerging Contaminants.” Princeton Hydro’s Director of Aquatic Programs Dr. Fred Lubnow is giving a presentation on “The Monitoring and Management of Cyanotoxins in Raw Water Supplies.” We hope to see you there! 

LEARN MORE

 

October 12: Association of New Jersey Environmental Commissions (ANJEC) 2018 Environmental Congress

ANJEC, a nonprofit organization supporting efforts to protect the environment and preserve natural resources in communities throughout New Jersey, is hosting its 45th Annual Environmental Congress at Mercer County College. The Environmental Congress is an annual statewide gathering of environmental commissions, local officials, agencies, citizen groups and environmental organizations, which includes an exhibitors hall, farmer’s market, and workshops on a variety of current environmental topics. Princeton Hydro, a business member of the ANJEC, will be exhibiting during the event. Stop by the booth to say hello to Dr. Stephen J. Souza, Princeton Hydro Founder and ANJEC Board of Trustees member, and Dana Patterson, Communications Strategist for Princeton Hydro.

LEARN MORE & REGISTER

 

October 23 – 25: New Jersey Association for Floodplain Management (NJAFM) 14th Annual Conference

NJAFM is hosting its 14th Annual Conference and Exhibition in Atlantic City, NJ. Participants will attend meetings and seminars covering topics, including hazard mitigation, flood insurance, infrastructure, mapping, planning, flood modeling, regulations, floodproofing, stormwater management, flood proofing, construction standards and more. Princeton Hydro’s Christiana Pollack, GISP, CFM and NJDEP’s Jessica Jahre, PP, AICP, CFM are giving a presentation, titled “A Flood Assessment for the Future,” for which they’ll showcase a flood assessment and flood mitigation analysis that Princeton Hydro performed in the Lower Moodna Creek Watershed.

LEARN MORE & REGISTER

 

October 23: “Undamming the Hudson River” Film Screening and Panel Event, Free & Open the Public

Riverkeeper and Patagonia present the premiere of “Undamming the Hudson River,” a short documentary film by National Geographic filmmaker Jon Bowermaster showcasing Riverkeeper’s efforts to restore natural habitat by eliminating obsolete dams throughout the Hudson River Estuary. The screening will be followed by refreshments and a panel discussion, moderated by Bowermaster, featuring experts in the field and an audience Q&A. Panelists, include:

  • Laura Wildman, PE – Water Resources and Fisheries Engineer, Princeton Hydro
  • George Jackman – Habitat Restoration Manager, Riverkeeper
  • Gwen McDonald – Director of Green Projects, Save the Sound
  • Andy J. Danylchuk, PhD – Associate Professor of Fish Conservation, UMASS Amherst, and Patagonia Fly Fishing Ambassador

This event is free and open to the public and will take place at Patagonia SoHo, 72 Greene St, New York, NY 10012 from 7:30 – 10pm.

RSVP HERE

 

October 24: Mid-Atlantic Chapter of the Urban & Regional Information Systems Association (MAC URISA) 2018 Conference

MAC URISA 2018, the largest GIS conference in the Mid-Atlantic region, will showcase outstanding and innovative uses of GIS technologies in the area. The program includes a variety of presentations, breakout sessions, a GIS Techspo forum, lightening talks, and more. Thomas Hopper, Princeton Hydro’s GIS Analyst, is providing a technical demonstration on the Linkage Mapper GIS Toolkit, which was created by the Nature Conservancy to support habitat connectivity analyses.

LEARN MORE & REGISTER HERE

 

October 30 – November 2: North American Lake Management Society (NALMS) Conference

NALMS is hosting its 38th International Symposium in Cincinnati Ohio, titled “Now Trending: Innovations in Lake Management.” This year’s symposium includes a robust exhibit hall, a variety of field trips, and a wide array of presentations on topics ranging from the latest in monitoring technologies to combating invasive species to nutrient and water quality management and more. Princeton Hydro’s Dr. Fred Lubnow, Director of Aquatic Programs, and Dr. Stephen Souza, Founder, both of whom have been members of NALMS since its inception, are presenting and exhibiting during the conference.

LEARN MORE

 

October 31 – November 2: Society for American Military Engineers (SAME) Small Business Conference (SBC)

SAME gives leaders from the A/E/C, environmental, and facility management industries the opportunity to come together with federal agencies in order to showcase best practices and highlight future opportunities for small businesses to work in the federal market. Princeton Hydro is proud to be attending the 2018 SAME SBC Conference, which is being held in New Orleans and co-locating with the Department of Veteran’s Affairs’ National Veterans Small Business Engagement. The program consists of networking events, small business exhibits, a variety of speakers and much more.

LEARN MORE & REGISTER

 

STAY TUNED FOR OUR NOVEMBER EVENT SPOTLIGHT!

Dam Removal Underway in Watertown, Connecticut

Deconstruction of the Heminway Pond Dam, Watertown, CT on July 16, 2018.

As dams age and decay, they can become public safety hazards, presenting a failure risk and flooding danger. 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.” Dam removal has increasingly become the best option for property owners who can no longer afford the rising cost of maintenance and repair work required to maintain these complex structures.

Dams can also cause environmental issues such as 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 can bring a river back to its natural state and significantly increase biodiversity for the surrounding watershed.

A view from the site of the Heminway Pond Dam removal on July 19, 2018.

Currently, work is underway in Watertown, Connecticut to remove the Heminway Pond Dam, which restricts fish passage in Steele Brook, creates a pond with increased water temperatures and high bacterial levels due to high geese populations, and encourages deposition of iron precipitate in the stream channel just downstream of the dam.

Princeton Hydro designed the engineering plans, managed permitting and is now overseeing construction for the removal project. The removal of the Heminway Pond Dam is identified as an integral component in addressing water quality impairment between the dam and Echo Lake Road.

CT DEEP recently published this piece encapsulating the Heminway Pond Dam removal project:

REMOVAL OF HEMINWAY POND DAM ON STEELE BROOK IN WATERTOWN UNDERWAY

Upstream at rock-filled breach in Heminway Pond Dam and shallow, dewatered impoundment on Steele Brook in Watertown (7-18-18)

After almost 15 years of discussion and planning with the Town of Watertown and other partners, removal of Heminway Pond Dam on Steele Brook in Watertown finally got underway in early July.  Though no longer functional, the dam and pond were originally constructed to supply water for a former thread/string mill.  The Town acquired the dam and pond from the Siemon Company, the most recent owner, in 2007 with an eye towards removing the dam, restoring the river and converting the dewatered impoundment area into a passive recreation area, including an extension of the Steele Brook Greenway.  With these goals in mind, the Town approached CT DEEP for help with removal of the dam.

As it turns out, CT DEEP, has also had a strong interest in seeing this dam removed.  It is anticipated that dam removal will improve the hydrology in this section of Steele Brook and eliminate a water quality impairment which manifests itself during hot weather and low flow conditions, as an orange-colored plume of water (due to iron precipitate) immediately downstream of the dam that impacts aquatic life.  Dam removal would also benefit fisheries by restoring stream connectivity and habitat.

Working towards these mutual goals, CT DEEP was able to provide federal CWA 319 nonpoint source grant funding to USDA NRCS to develop a watershed-based plan for Steele Brook to address nonpoint source impairments that includes a dam removal feasibility analysis for Heminway Pond Dam.  Based on the recommendations in this plan, CT DEEP subsequently provided additional 319 grant funds to the Town of Watertown to hire a consultant to develop a dam removal design package, and assist with permitting and preparation.

With the Town of Watertown as a strong and vested partner, CT DEEP is now helping this project over the finish line by providing a combination of 319 and SEP funds to accomplish the actual dam removal and restoration of Steele Brook.  Dayton Construction Company is performing the construction and Princeton Hydro is the consultant overseeing the project on behalf of the Town.  The Northwest Conservation District is also assisting with the project.  It is anticipated that the majority of the work will be completed by this Fall.  U.S. EPA, ACOE and CT DEEP have all played active roles with regard to permitting the project.

 

A view of the first notch during the Heminway Pond Dam removal on July 17, 2018.

Princeton Hydro has designed, permitted, and overseen the reconstruction, repair, and removal of dozens of small and large dams in the Northeast. Click here to read about a recent dam removal project the firm completed on the Moosup River. And, to learn more about our dam and barrier engineering services, visit: bit.ly/DamBarrier.

Creative, Timely Solutions Lead to Successful Dam Repair in Medford Lakes

By Kevin Yezdimer, P.E. and Jim Hunt, P.E.

Just 25 miles east of Philadelphia, on the edge of the New Jersey Pinelands region, sits a network of 22 lakes that serve a multitude of recreation purposes for the residents of Medford Lakes. Serving as the guardian to these natural beauties is the Medford Lakes Colony (MLC), a private homeowner association. Homeowners in this community contribute to a “Lake Restoration Fund,” managed by MLC, which is used to maintain the water control structures and monitor the water quality for the bodies of water within the community. This dedicated fund is often used for dredging of the lake beds; repairs and replacement of dams, spillways, and culverts; installation of aerators or fountains to promote long-term benefits to water quality; treatments for weeds and algae; and the maintenance of the coves and beaches.

In mid-April, a concerning blockage developed in Lake Wauwauskashe Dam’s spillway and water was backing up at the upstream outlet structure. The 30-inch wide corrugated metal pipe serves as the dam’s primary (and only) outlet under Wagush Trail, a neighborhood road connecting Lake Wauwauskashe and Lake Mushkodasa. During the attempt to clear the mass of accumulated woody-debris via vacuum truck extraction, a previous repair consisting of a 5’ segment of corrugated plastic pipe had been dislodged and expelled from the downstream end of the spillway. With a compromised dam and flooding in the forecast, MLC acted immediately to handle this emergency dam repair.

Primary Spillway Inlet
Before – Upper portion of the existing corrugated metal pipe was collapsed. After – Pipe was slip-lined and the annulary space was grouted.

 

Given Princeton Hydro’s long-term history of inspecting and maintaining dams and levees in Medford Lakes, MLC contracted our experts to assist. The next day, our team of geotechnical engineers were on-site to investigate the situation. To facilitate the inspection and minimize the stress/pressure on the dam, the upstream and downstream lakes were lowered via an NJDEP Fish and Wildlife Lake Lowering Permit. Additionally, a video inspection of the compromised culvert pipe was conducted. Our geotechnical team observed that the upstream portion of the pipe had collapsed and the structure was experiencing significant seepage (i.e. water flowing through undesirable paths through the dam with the potential for soil piping and stability failure).

Primary Spillway outlet
Before – The existing corrugated metal pipe had corroded and erosion had taken place around the outlet. After – Pipe has been slip-lined and outlet protection (riprap) was installed to stabilize the surrounding soil.

 

With the risk of potential dam failure, Princeton Hydro immediately kicked-off coordination with the NJDEP Bureau of Dam Safety, NJDEP Division of Land Use Regulation, the Pinelands Commission, and the Borough of Medford Lakes. Our licensed engineers promptly developed the repair concept and associated scope of work, detailing our proposed means and methods for the emergency repair.

“We take the potential risk of dam failure very seriously, as safety is one of our core values,” said Kevin Yezdimer, P.E. Director of Geosciences Engineering at Princeton Hydro. “Our geotechnical team prioritized the design, permitting, and implementation of this emergency repair to assure the safety of our client and the community.”

Injection grouting underway (Grout pressure is monitored during placement & the ground surface is monitored for signs of heave).

This included addressing the collapsed pipe; utilizing cementitious injection grouting and compaction grouting to eliminate seepage pathways and stabilize the earthen dam in-place; and provide spillway outfall protection. Through private solicitation, Princeton Hydro selected Compaction Grouting Services, Inc. as the specialty contractor to perform the repair.

A considerable volume of water was required to prepare the grout mixes, and no water sources were available adjacent to the project site. Seeking out solutions, MLC proposed the unique idea of using reclaimed wastewater from the local wastewater treatment plant. Our team confirmed that reuse of the reclaimed wastewater was indeed within the guidelines of the “Technical  Manual for Reclaimed Water for Beneficial Reuse,” and we successfully facilitated approval to use it with NJDEP Division of Water Quality.

Placement of cellular fill into the hollow concrete structure is underway. A lightweight foaming agent was added to the grout mix within the concrete truck. The lightweight grout was then pumped into the structure.

As the construction effort ramped-up, some complications arose. By design, this unique structure allows water flow over the dam’s weirs and drops 8 to 10 feet vertically before travelling under the roadway through the primary spillway. Above the primary spillway is a concrete structure that spans from the upstream lake to the downstream lake and immediately beneath the local roadway. It was discovered that this 50’ long, 6’ deep, concrete structure was hollow and served as a potential seepage pathway. Princeton Hydro proposed to fill-in the hollow structure with a lightweight cellular fill material in order to cut-off the potential seepage pathways, eliminate the 6’ deep hollow chamber beneath the roadway, and facilitate a long-term repair solution.

Implementation of this strategy was further complicated when a utility markout and a subsequent video inspection of the hollow structure confirmed that a gas line passed through the structure on the downstream side of the roadway. Princeton Hydro coordinated with South Jersey Gas to disconnect the gas line in order to minimize risk during construction and eliminate future complications. The neighborhoods on either side of the dam were fed redundantly, so their service was not interrupted during this process.

Overall, the emergency dam repair solution involved an in-situ soil stabilization of an earthen embankment dam via compaction/injection grouting, slip-lining the primary spillway, stabilization of the downstream outlet, and utilization of reclaimed wastewater as a water source for on-site grout batching. The following was completed by our team and contractors during the course of the emergency construction:

  • Slip-lining of the failed 30-inch pipe using a smooth, slightly smaller in diameter high density polyethylene pipe (HDPE) pipe inside of the existing pipe, providing an equal or greater hydraulic capacity as that existing;

  • Grouting of the annular space between the new and old pipes;

  • Non-woven geotextile fabric and riprap outfall protection were placed around the downstream outlet of the culvert pipe to provide scour protection;

  • Compaction and injection grouting was performed in multiple locations. The compaction grout utilized a “low-slump” mix while the injection grout utilized a much more mobile or fluid mix allowing for filling of existing seepage pathways or soil voids, and;

  • Approximately 44 cubic yards of lightweight cellular-grout backfill was utilized to fill in the hollow concrete structure beneath the roadway completing the emergency repair without the need for complete outlet structure or earthen dam reconstruction.

Lowering New Pipe Into Place

Creative, innovative solutions paired with timely coordination and expertise drove the success of the Lake Wauwauskashe Dam emergency repair.

Princeton Hydro has designed, permitted, and overseen the reconstruction, repair, and removal of a dozens of small and large dams in the Northeast. To learn more about our dam and barrier engineering services, visit: bit.ly/DamBarrier.

Kevin M. Yezdimer, P.E., Princeton Hydro’s Geoscience Engineering Director, is a multidisciplinary professional civil engineer who holds degrees in both Geology and Civil Engineering, and has 11 years of progressive and varied work experience as both a design consultant and project owner with Geotechnical & Construction Engineering being his core area of expertise. He has significant experience performing soil and rock core sampling programs, infiltration testing, soils laboratory testing, foundation design (shallow and deep), preparation of construction recommendations,  and overseeing construction review activities (e.g., earthwork, foundations, concrete, masonry, structural steel, roadway, and utility construction).

 

Jim Hunt, P.E., joined Princeton Hydro in 2017 as a Geotechnical Engineer and provides a wide range of engineering services for the firm including: subsurface explorations, bearing capacity and settlement analyses, slope stability analysis, stability analysis of existing structures, preparation of technical deliverables, and cost estimating.