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.

Fish Passage Restored on the Paulins Kill

A view of where the Columbia Lake Dam used to reside. February 19, 2019. Photo courtesy of Casey Schrading, Staff Engineer, Princeton Hydro

On the Paulins Kill, the 100-year old Columbia Lake Dam has almost been completely removed, and fish passage has been restored!  Since the first cut was executed on the main dam in August, many exciting advances have been made towards restoring the Paulins Kill back to its natural state. Check out the video below, courtesy of the New Jersey Nature Conservancy Volunteer Drone Team. 

Piece by piece, the dam was notched out throughout the fall season and is now completely removed with the exception of the dam apron, the horizontal concrete structure that sits downstream of the dam, and the section of the dam that sits below the riverbed. The part of the dam in the riverbed is now being removed all the way down  to three feet under the ground. The full removal is estimated to be complete by mid-March. In mid-August, the first cut was widened to 80 feet, allowing for better management of high flows during storm events, which had been posing a challenge immediately following the first cut.

In late August, the installation of rock vanes at the Brugler Road Bridge began. Rock vanes are engineered, in-stream structures that help to stabilize a channel while enhancing aquatic habitat and movement.

A generic schematic example of cross vanes, this is not the exact engineering plan for this specific project. Photo courtesy of North Carolina Cooperative Extension.

The rock vanes installed at the Brugler Road Bridge site are cross vanes. Cross vanes consist of a set of boulders angled upstream on a river, with another section of smaller rocks placed upstream. The taller sections of the cross vanes deflect the streamflow away from the banks, decreasing scouring effects. Instead, the flow travels over the rock walls and concentrates down the center of the channel, creating a deep and elongated pool in the middle of the stream.  

Velocities between the notches in the rock vanes were evaluated using a velocity meter in accordance with the design specifications originally proposed. Based on the U.S. Fish and Wildlife Service fish passage design criteria, velocities in the notches could not be greater than 8.25 feet per second. All of the velocity measurements in this rock vane were below the maximum thresholds, ensuring no blockage of fish passage is made through the vanes.

Since the removal of the dam began, vegetative growth from the natural seedbed of the upper impoundment has been observed (see photo below).

In October, scour protection installation commenced at the Warrington Road Bridge site. After the team conducted geotechnical test pits, they discovered that a concrete scour wall that slopes out to the Paulins Kill was present and deep enough to be able to install rock at the necessary depth. They also found that the existing gabions, caged baskets filled with rock or concrete often used to protect against erosion, were intact and could be left in place. The team installed four (4) feet of riprap under and around the bridge in the riverbed and tied it into the existing grade of the banks.

The original notch in the dam was lowered one foot per day starting in mid-December, reducing water surface elevations down to the apron elevation during the month of January.

To accommodate NJ Fish and Wildlife’s request for animal passage under the I-80 bridges, an area of the previously installed riprap on the northwest abutment wall was flattened out and filled in with river cobble. This path will promote wildlife movement under the bridge as opposed to through the existing tunnel.

Currently, rock vanes are being installed under the I-80 bridges specifically to enhance fish passage. These structures vary slightly from the rock vanes at the Brugler Road Bridge site, as they are designed to slow river flow, helping migrating fish travel upstream and traverse a 5-foot elevation difference in the streambed, much like a fish ladder

These rock vanes are more than halfway completed and are on track to be finished in time for fish populations to make full use of them.  The next steps are to finish the demolition of the dam and the construction of the fish passage rock vanes under the I-80 bridges, plant vegetation throughout the upper impoundment, create a recreational trail through the upper impoundment, and plan for fishing and boating access! Stay tuned for more exciting developments on this incredible project.

Thank you to our project partners: The Nature Conservancy, American Rivers, U.S. Fish and Wildlife Service, and NJDEP Division of Fish and Wildlife Service.

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 fish passage and dam removal engineering services, visitbit.ly/DamBarrier.

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

Employee Spotlight: Meet Our New Team Members

We’re excited to welcome four new members to our team. The addition of this group of talented individuals strengthens our commitment to delivering great service that exceeds our clients’ expectations.

Meet Our New Team Members
Miranda Lepek, EIT, Water Resource Engineer

Miranda is a civil engineer with expertise in grading and stormwater design, CAD drafting, environmental sampling, and construction oversight. Prior to Princeton Hydro, she worked for a small site development firm in Michigan where she developed her drafting skills and facilitated multiple aspects of private and commercial land development projects.

Miranda holds a B.S. in Civil Engineering from the University of Michigan – Ann Arbor. While on study abroad, she contributed to the one of the longest-running native amphibian field studies in New Zealand. In other previous experiences, she worked on major projects including the investigation phases of a Superfund site cleanup in Duluth, MN and a comprehensive sampling operation over 40 miles of the Hudson River near Albany, NY. In her free time, Miranda enjoys hiking, foraging, cooking and art.

Sumantha Prasad, PE, ENV SP, Water Resource Engineer

Sumantha is a Water Resource Engineer with a B.S. in Bioenvironmental Engineering from Rutgers University and a M.S. in Environmental Engineering and Science from Johns Hopkins University. She worked in Maryland for seven years focusing on ecological restoration projects, including stream restoration, wetland creation and enhancement, and stormwater management, and she worked for 3 years with a primary focus on highway hydrology and hydraulics.

In her spare time, she enjoys being a Toastmaster and serves as the Treasurer to a 501(c)3 organization dedicated to creating inclusive housing communities for adults with disabilities. She also enjoys telling terrible puns unapologetically.

Pat Rose, Environmental Scientist

Pat’s interest in aquatics began 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, Tennessee as part of a Water Quality Team. While in Tennessee, Pat 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. During his year with AmeriCorps, Pat worked with government organizations to perform biological sampling and erosion monitoring in local streams.

Pat graduated from SUNY Oneonta with a M.S. in Lake Management in December 2018. During his time in graduate school, 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.

Duncan Simpson, Senior Environmental Scientist

For nearly a decade, Duncan has served as an Environmental Scientist/Planner in the Mid-Atlantic Region. His experience includes a wide range of natural resource studies, documentation, and permitting at both the project and program level. He has special expertise in wetlands; Waters of the US delineations; and permitting for stormwater management facilities, stream restoration, and TMDL program projects. He has conducted forest stand delineations; rare, threatened and endangered species consultations; mitigation monitoring; and National Environmental Policy Act (NEPA) documentation.

Duncan holds an M.S in Biology from Towson University and a B.S. in Environmental Science with a Wildlife and Fisheries Conservation Minor from the University of Massachusetts. During his graduate studies, he researched amphibian species found in Delmarva Bays and testing models that predict their presence based on abiotic habitat characteristics. He also served as a student member of the Northeast Partners in Amphibian and Reptile Conservation (NEPARC) steering committee. Duncan is a Professional Wetland Scientist and member of the Society of Wetland Scientists. In his spare time, he enjoys hiking with his dog and learning how to fly fish.

 

Employee Spotlight: Helping Communities Around the World Access Water Resources

We’re Proud to Put the Spotlight on Natalie Rodrigues, Staff Engineer And Engineers Without Borders Co-President

As a staff engineer specializing in water resources, Natalie Rodrigues, EIT, CPESC-IT works on a wide range of projects from stormwater management to ecosystem restoration to dam safety. Outside of the office, Natalie is an active volunteer with Engineers Without Borders (EWB), a nonprofit organization that works to build a better world through engineering projects that aid communities in meeting their basic needs.

EWB volunteers work with communities in the U.S. and throughout the world to find appropriate solutions for their infrastructure needs, including clean water supply; sanitation; sustainable energy; structures like bridges and buildings; and various agriculture essentials from irrigation systems to harvest processing.  Natalie began volunteering for the organization six years ago while attending college at the SUNY College of Environmental Science and Forestry where she earned her Bachelor of Science in Environmental Resources Engineering with a focus in water resources.

Natalie and Lola, a student from the elementary school in Guatemala where Natalie assisted on an EWB project to install a latrine system

Her first big volunteer project, which was done in collaboration with EWB’s Syracuse Professionals Chapter, was designing and building a system of composting latrines for an elementary school in the small town of Las Majadas, Guatemala. Natalie provided assistance on several aspects of the project, including working on a Health and Safety Plan. The completion of this project helped to prevent the spread of disease, as well as treat waste without the need for a constant water supply/sewer system. The long-lasting design also increases the health practices and hygiene of the community, creating a safer place for education.

Natalie also served as secretary of the university’s EWB chapter for two years, then became the Regional Administrator for the Northeast Regional Committee, and is now starting her third year as a Co-President of the region.

In her current role with the regional committee, Natalie helps to provide resources for members and facilitates communication between EWB Headquarters and individual chapters. She assists with various mini-conferences and workshops throughout the region and provides opportunities for members to obtain Professional Development Hours and certifications. She is also a part of the EWB’s Diversity and Inclusion Task Force and the Council of Regional Presidents.

Natalie stands with her 2018 Northeast Regional Committee members at the 2018 National Conference

We’re so proud to have Natalie on our team and truly value the work she does inside and outside the office.

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.

 

New Green Infrastructure Toolkit for Municipalities

Our partner, New Jersey Future, just launched a brand new, interactive website toolkit to help municipalities across the state incorporate green infrastructure projects into their communities. The New Jersey Green Infrastructure Municipal Toolkit will provide expert information on planning, implementing, and sustaining green infrastructure to manage stormwaterThis toolkit acts as a one-stop resource for community leaders who want to sustainably manage stormwater, reduce localized flooding, and improve water quality.

According to the United States EPA, a significant amount of rivers, lakes, ponds, bays, and estuaries in New Jersey fall into the “Impaired Waters” category, meaning that one or more of their uses are not being met. This reality makes green infrastructure more important than ever in the effort to protect our waterways. When it rains, stormwater creates runoff, which often carries pollution to various types of waterbodies. Green stormwater infrastructure helps to absorb and filter rainwater, reducing the pollution entering our waterways and mitigating flooding in our communities. In urban areas, green infrastructure utilizes natural vegetation to divert stormwater, creating a cost-effective and aesthetically-pleasing way to manage water during rain events.

“We designed this toolkit to bring to light the benefits and importance of investing in green infrastructure at the local level,” said Dr. Stephen Souza, co-founder of Princeton Hydro. “Since the current NJ stormwater rules do not require green infrastructure, we hope to inspire municipal engineers and planning board members to believe in the value through our toolkit. Additionally, we hope it will serve as an educational resource to local officials and decision makers in the Garden State.”

For this project, Princeton Hydro was contracted by Clarke Caton Hintz, an architecture, design, and planning firm, leading this effort on behalf of the nonprofit organization New Jersey Future. Our expert engineers and scientists provided real-world examples integrating green infrastructure into development, in hopes of showing those using the toolkit real world evidence of how green infrastructure can be a part of the daily lexicon of stormwater management. Additionally, Dr. Stephen Souza developed performance standards that municipalities can integrate into stormwater management plans, which are available in the Green Infrastructure Municipal Toolkit.

Mitigation Milestone Reached at Mattawoman Creek Mitigation Site

Photo courtesy of GreenVest

Mattawoman Creek Mitigation Project will Restore and Protect 80+ Acres of Mattawoman Creek, Chesapeake Bay’s Most Productive Tributary

As one of the Chesapeake Bay’s most productive tributaries and a vital part of Maryland’s natural resources, Mattawoman Creek supports some of the largest populations of finfish, amphibians, and birds in the state. A collaborative team of private and public sector entities have designed the “Mattawoman Creek Mitigation Site” in Pomfret, Charles County, Maryland, an effort that will enhance or create 64+ acres of wetlands and restore nearly 3,800 linear feet of this perennial stream.  With over 28,500 native trees and shrubs to be planted, this mitigation project will result in 80+ acres of continuous, forested wetland with complex and diverse vegetative communities. It is expected to provide a wide array of habitat to resident and transient wildlife, including birds, reptiles, invertebrates, amphibians and rare, threatened and endangered species.

Unique to this project, Mattawoman Creek Mitigation Site is Maryland’s first-ever Umbrella Mitigation Banking Instrument (UMBI) for federal and other government agency use.   A UMBI is the bundling of multiple mitigation banks into one agreement in order to streamline the regulatory approval process, thereby eliminating steps and involving fewer resources. The Maryland UMBI document helps the USAF and other public agencies secure certainty of cost and schedule, facilitate timely permit issuance, and expedite the satisfaction of their permitted requirements for planned capital improvement projects. This approach also maximizes the scale of restoration and resulting land protection and efforts, creating contiguous blocks of habitat with greatly enhanced benefits compared to single, permittee-responsible projects. This precedent was a result of a partnership between United States Air Force (USAF) and Joint Base Andrews (JBA), U.S. Army Corps of Engineers (USACE), Maryland Department of the Environment (MDE), GreenTrust Alliance, GreenVest, and Princeton Hydro.

Projects completed under the UMBI will reduce federal and state workload expediting the regulatory review and issuance of permits by the MDE and USACE. Additionally, projects completed under this UMBI will aid in compliance with the Federal Paperwork Reduction Act where federal regulatory staff can evaluate success and performance issues for multiple permittees at one single habitat restoration or mitigation site. In addition, federal costs are capped, and liabilities  are transferred through to GreenVest, the private sector operator, and GreenTrust Alliance, the nonprofit bank sponsor, who will also serve as the long-term steward of sites restored under this program.

Pictured is the southern restoration area after
sorghum germination, prior to wetland creation
and reestablishment.
A function-based stream assessment was
performed on the degraded channel.

 

Photo courtesy of GreenVestDesign, engineering/modeling, and permitting of the site was completed by  Princeton Hydro and GreenVest under our currently Ecosystem Restoration contract with the USACE. Princeton Hydro also provided an Environmental Assessment and Environmental Baseline Survey, and conducted a geotechnical investigation, which included the advancement of test pits, visual and manual investigation techniques and logging, infiltration testing, laboratory soils testing, and seasonal high-water table estimations.

A wetland water budget was also developed for the proposed wetland creation and restoration to determine if sufficient water is available to establish or reestablish wetlands on the site. It was also used to inform design development including proposed grading and plant community composition. The establishment and re-establishment of wetlands on the site will be accomplished through directed grading, ditch plugging and stream restoration designed to maximize the retention of surface water, floodplain re-connection, and groundwater inputs.

Highlights from the Mattawoman Creek Wetland and Stream Mitigation project:
  • 80 acres of land were placed into conservation easement and removed from active row crop production and cattle pasture. The easement, which is held by GreenTrust Alliance, provides permanent protection for all 80 acres.
  • Over 64 acres of wetlands will be restored, created, enhanced or preserved, which will sequester approximately 75 tons of carbon per year.
  • 3,798 linear feet of perennial stream will be restored by re-establishing, historic floodplain access during more frequent storm events, stabilizing hydraulics and geomorphology, and adding aquatic habitat value.
  • Full integration of the wetland and stream restoration elements will occur exponentially, increasing anticipated functions and values in the post construction condition. Functions include: storm damage and flood attenuation, groundwater recharge and discharge, nutrient cycling and sequestration, local water quality improvement, and wildlife habitat enhancements.
  • This project will also create and enhance the forested wetland and stream habitat for the State-listed Threatened Selys’ Sundragon (Helocordulia selysii).
  • As part of the site design, over 28,500 native trees and shrubs will be planted.
  • The Mattawoman Creek Mitigation Site is located within a Tier 3 Biodiversity Conservation Network area. These areas are classified by the Department of Natural Resources as “highly significant for biodiversity conservation” and are priority conservation areas that support critical species and habitats.
  • The project will yield advanced mitigation values: 7.913 in wetland credits and 1,595 in stream credits. These credits are durable and will be available for JBA’s use in order to satisfy permitted impacts associated with planned capital improvement projects.

Over 6,000 acres (25%) of the Mattawoman Creek watershed has been protected by public ownership and various conservation and agricultural easements, which, in addition to the Mattawoman Creek Mitigation Site, help ensure that Mattawoman Creek forever remains a high-quality destination for outdoor recreation.

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