Analyzing Mitigation Strategies for Flood-Prone Philadelphia Community

Photo from Eastwick Friends and Neighbors Coalition

Hydrology is the study of the properties, distribution, and effects of water on the Earth’s surface, in the soil and underlying rocks, and in the atmosphere. The hydrologic cycle includes all of the ways in which water cycles from land to the atmosphere and back. Hydrologists study natural water-related events such as drought, rainfall, stormwater runoff, and floods, as well as how to predict and manage such events. On the application side, hydrology provides basic laws, equations, algorithms, procedures, and modeling of these events.

Hydraulics is the study of the mechanical behavior of water in physical systems. In engineering terms, hydraulics is the analysis of how surface and subsurface waters move from one point to the next, such as calculating the depth of flow in a pipe or open channel. Hydraulic analysis is used to evaluate flow in rivers, streams, stormwater management networks, sewers, and much more.

Combined hydrologic and hydraulic data, tools, and models are used for analyzing the impacts that waterflow – precipitation, stormwater, floods, and severe storms – will have on the existing infrastructure. This information is also used to make future land-use decisions and improvements that will work within the constraints of the hydrologic cycle and won’t exacerbate flooding or cause water quality impairment.

Simply put, hydrologic and hydraulic modeling is an essential component of any effective flood risk management plan.

Putting Hydrologic & Hydraulic Analysis to Work in Philadelphia

Eastwick, a low-lying urbanized neighborhood in Southwest Philadelphia, is located in the Schuylkill River Watershed and is almost completely surrounded by water: The Cobbs and Darby creeks to the west, the Delaware River and wetlands to the south, and the Schuylkill River and Mingo Creek to the east. The community is at continual risk of both riverine and coastal flooding, and faces an uncertain future due to sea level rise and riverine flooding exacerbated by climate change.

Princeton Hydro, along with project partners KeystoneConservation and University of Pennsylvania, conducted an analysis of Eastwick, the flood impacts created by the Lower Darby Creek, and the viability of several potential flood mitigation strategies.

Flood mitigation approaches can be structural and nonstructural. Structural mitigation techniques focus on reconstructing landscapes, including building floodwalls/seawalls and installing floodgates/levees. Nonstructural measures work to reduce damage by removing people and property out of risk areas, including zoning, elevating structures, and conducting property buyouts.

For Eastwick, studying stream dynamics is a key component to determining what type of flood mitigation strategies will yield the most success, as well as identifying the approaches that don’t work for this unique area.

Princeton Hydro Senior Ecologist Christiana Pollack CFM, GISP participated in a workshop for Eastwick residents held by CCRUN and the Lower Darby Creek team. The goal of the workshop was to get the community’s input on the accuracy of the predictive models.Princeton Hydro’s study focused on the key problem areas in Eastwick: the confluence of Darby Creek and Cobbs Creek; a constriction at Hook Road and 84th Street; and the Clearview Landfill, which is part of the Lower Darby Creek Superfund site. Additionally, the study sought to answer questions commonly asked by community members related to flooding conditions, with the main question being: What impact does the landfill have on area flooding?

The built-up landfill is actually much higher than the stream bed, which creates a major disconnection between the floodplain and the stream channel. If the landfill didn’t exist, would the community still be at risk? If we increased the floodplain into the landfill, would that reduce neighborhood flooding?

Princeton Hydro set out to answer these questions by developing riverine flooding models primarily using data from US Army Corps of Engineers (USACE), Federal Emergency Management Agency (FEMA), The National Oceanic and Atmospheric Administration (NOAA), and NOAA’s National Weather Service (NWS). FEMA looks at the impacts of 1% storms that are primarily caused by precipitation events as well as coastal storms and storm surge. NOAA looks at the impacts of hurricanes. And, NOAA’s NWS estimates sea, lake and overland storm surge heights from hurricanes.

This is an example of a 2D model showing where the water is originating, how the water flows through the neighborhood, moves to the lower elevations, and eventually sits.

This is an example of a 2D model showing where the water is originating, how the water flows through the neighborhood, moves to the lower elevations, and eventually sits.

The models used 2D animation to show how the water flows in various scenarios, putting long-held assumptions to the test.

The models looked at several different strategies, including the complete removal of the Clearview Landfill, which many people anticipated would be the silver bullet to the area’s flooding. The modeling revealed, however, that those long-held assumptions were invalid. Although the landfill removal completely alters the flood dynamics, the neighborhood would still flood even if the landfill weren’t there. Additionally, the modeling showed that the landfill is actually acting as a levee for a large portion of the Eastwick community.

This model was developed to illustrate how the removal of the landfill impacts waterflow through the Eastwick community.

This model was developed to illustrate how the removal of the landfill impacts waterflow through the Eastwick community.

Ultimately, the research and modeling helped conclude that for the specific scenarios we studied, altering stream dynamics – a non-structural measure – is not a viable flood mitigation strategy.

The USACE is currently undergoing a study in collaboration with the Philadelphia Water Department to test the feasibility of a levee system (a structural control measure), which would protect the Eastwick community by diverting the flood water. Funding for the study is expected to be approved in the coming year.

Take a Deeper Look at Eastwick Flood Mitigation Efforts

There are many studies highlighting flood mitigation strategies, environmental justice, and climate change vulnerability in Eastwick. Princeton Hydro Senior Project Manager and Senior Ecologist, Christiana Pollack CFM, GISP, presented on the flooding in Eastwick at the Consortium for Climate Risk in the Urban Northeast Seminar held at Drexel University. The seminar also featured presentations from Michael Nairn of the University of Pennsylvania Urban Studies Department, Ashley DiCaro of Interface Studios, and Dr. Philip Orton of Stevens Institute of Technology.

You can watch the full seminar here:

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

Managing Invasive Phragmites and Restoring Natural Wetland Habitat

Non-native Phragmites australis, also known as Common Reed, is a species of perennial grass found across North America, especially along the Atlantic coast, in wetlands, riparian areas, shorelines, and other wet areas like roadside ditches and drainage basins. This aggressively invasive grass can grow up to 20 feet tall, in dense groupings, and tends to spread rapidly, quickly colonizing disturbed wetlands.

Once established, the invasive plant forms a monoculture with a dense mat, outcompeting native vegetation, lowering the local plant biodiversity, and displacing native animals. These landscape changes impair the natural function of the marsh ecosystem by altering its elevations and tidal reach. A higher, drier marsh leads to less vigorous growth of native salt marsh vegetation, allowing Phragmites australis to gain a stronger foothold and continue to take over.

USDA NRCS Plants Database phragmites illustrationPhragmites australis can also eliminate small, intertidal channels and obliterate pool habitat that offers natural refuge and feeding grounds for invertebrates, fish, and birds. The spread of invasive Phragmites australis also has negative impacts on land aesthetics and outdoor recreation by obscuring views and restricting access. And, each Fall, when Phragmites australis die off, the large concentrations of dry vegetation increase the risk of fast-spreading fires near highly populated residential and commercial areas.

Over the last century, there has been a dramatic increase in the spread of Phragmites australis, partly due to an increase in residential and commercial development that resulted in disturbances to wetlands. According to the U.S. Fish and Wildlife Service, the rapid spread of Phragmites australis in the 20th century can also be attributed to the construction of railroads and major roadways, habitat disturbance, shoreline development, pollution, and eutrophication.

Princeton Hydro has worked in areas throughout the East Coast to address and properly manage Phragmites australis in order to restore natural habitats and enhance plant diversity, wildlife habitat, and water quality. Two recent projects include the restoration of John A. Roebling Memorial Park in Hamilton and Pin Oak Forest Conservation Area in Woodbridge, New Jersey.

John A. Roebling Memorial Park

Mercer County’s John A. Roebling Memorial Park is home to the northernmost freshwater tidal marsh on the Delaware River, the Abbott Marshlands, an area containing valuable habitat for many rare species. Unfortunately, the area experienced a significant amount of loss and degradation, partially due to the introduction of the invasive Phragmites australis.

For Mercer County Park Commission, Princeton Hydro put together a plan to reduce and control the Phragmites australis, in order to increase biodiversity, improve recreational opportunities, and enhance visitor experience at the park. This stewardship project replaced the Phragmites australis with native species in order to reduce its ability to recolonize the marsh.

By Spring of this year, the team expects to see native species dominating the landscape from the newly exposed native seed bank with minimal Phragmites australis growth.

Pin Oak Forest Conservation Area

The Pin Oak Forest Conservation Area is a 97-acre tract of open space that contains an extremely valuable wetland complex at the headwaters of Woodbridge Creek. The site is located in a heavily developed landscape of northern New Jersey. As such, the area suffered from wetland and stream channel degradation, habitat fragmentation, ecological impairment, and decreased biodiversity due to invasive species, including Phragmites australis.

The site was viewed as one of only a few large-scale freshwater wetland restoration opportunities remaining in this highly developed region of New Jersey. A dynamic partnership between government agencies, NGOs, and private industry, was formed to restore the natural function of the wetlands complex, transform the Pin Oak Forest site into thriving habitat teeming with wildlife, and steward this property back to life.

This award-winning restoration project converted over 30 acres of degraded freshwater wetlands, streams and disturbed uplands dominated by invasive species into a species-rich and highly functional headwater wetland complex. The resulting ecosystem provides valuable habitat for wildlife including the state-threatened Black-crowned Night-heron and Red-headed Woodpecker. Biodiversity was also increased through invasive species management, which allowed establishment of native plants such as pin oak, swamp white oak, marsh hibiscus, and swamp rose. The restored headwater wetland system provides stormwater management, floodplain storage, enhanced groundwater recharge onsite, and surface water flows to Woodbridge Creek, as well as public hiking trails, all benefiting the town of Woodbridge.

Managing and Monitoring Phragmites

Scientific field research continues to be conducted in order to identify the best way(s) to manage and control the spread of Phragmites australis. Depending on the landscape and how established the Phragmites australis population is, there are several different methods that can be effective in reducing Phragmites australis infestations in order to allow for the regeneration of native wetland plant communities and protect fish and wildlife habitat.

Recently, a group of more than 280 scientists, resource managers and policy professionals gathered together at the Hudson River Estuary Program’s (HEP) annual conference to explore how natural and nature-based solutions (i.e. building living shorelines, enhancing tidal wetlands and stream corridors, and conserving vulnerable floodplains) can be used as critical tools for addressing the impacts of climate change while also protecting and enhancing critical habitat.

The conference included six interactive workshops and dynamic panel discussions. Christiana Pollack, GISP, CFM of Princeton Hydro, Terry Doss of New Jersey Sports and Exposition Authority, Kip Stein from New York City Parks, and Judith Weis of Rutgers lead a panel discussion, moderated by Lisa Baron from U.S. Army Corps Engineers, on “The Yin and Yang of Estuarine Phragmites Management” to share lessons learned over many years of combating invasive species, including how sea level rise is changing minds and techniques.

Together, representing decades of experience in Phragmites australis management and research, these experts presented the evolving nature of restoration for this habitat type, common control/management methodologies, and longterm management and monitoring strategies for this reed and other invasive species. During the panel discussion, Christiana made specific mention of the Roebling Park project as one example of successful strategies in action.

If you’re interested in learning more and seeing photos from a few recent Phragmites australis management projects, click below for a free download of Christiana’s full presentation.

Through a combination of prevention, early detection, eradication, restoration, research and outreach, we can protect our native landscapes and reduce the spread of invasive species. Learn more about our invasive species removal and restoration services.

 

Feasibility Study Identifies Key Opportunities for Hudson River Habitat Restoration

Hudson River Bear Mountain Bridge (Photo from Wikipedia)

The Hudson River originates at the Lake Tear of the Clouds in the Adirondack Mountains at an elevation of 4,322 feet above sea level. The river then flows southward 315 miles to New York City and empties into the New York Harbor leading to the Atlantic Ocean. The Hudson River Valley lies almost entirely within the state of New York, except for its last 22 miles, where it serves as the boundary between New York and New Jersey.

Hudson River Basin (Image by USACE)Approximately 153 miles of the Hudson River, between the Troy Dam to the Atlantic Ocean, is an estuary. An estuary is defined by the USEPA as “a partially enclosed, coastal water body where freshwater from rivers and streams mixes with salt water from the ocean. Estuaries, and their surrounding lands, are places of transition from land to sea. Although influenced by the tides, they are protected from the full force of ocean waves, winds and storms by landforms such as barrier islands or peninsulas.”

The Hudson River’s estuary encompasses regionally significant habitat for anadromous fish and globally rare tidal freshwater wetland communities and plants, and also supports significant wildlife concentrations. As a whole, the Hudson River provides a unique ecosystem with highly diverse habitats for approximately 85% of New York State’s fish and wildlife species, including over 200 fish species that rely on the Hudson River for spawning, nursery, and forage habitat.

The Hudson is an integral part of New York’s identity and plays a vital role in the lives of the people throughout the area. Long valued as a transportation corridor for the region’s agricultural and industrial goods, and heavily used by the recreation and tourism industries, the Hudson plays a major role in the local economy. It also provides drinking water for more than 100,000 people.

At the end of the American Revolution, the population in the Hudson River Valley began to grow. The introduction of railroad travel in 1851 further accelerated development in the area. Industrial buildings were erected along the river, such as brick and cement manufacturing, which was followed by residential building. Along with the aforementioned development, came the construction of approximately 1,600 dams and thousands of culverts throughout the Hudson River.

According to the U.S. Army Corps of Engineers (USACE), these human activities have significantly degraded the integrity of the Hudson River ecosystem and cumulatively changed the morphology and hydrology of the river. Over time, these changes have resulted in large-scale losses of critical shallow water and intertidal wetland habitats, and fragmented and disconnected habitats for migratory and other species. Most of this loss and impact has occurred in the upper third portion of the estuary.

As part of the effort to restore the vital river ecosystem, the USACE New York District launched a Hudson River Habitat Restoration Feasibility Study, which helps to establish and evaluate baseline conditions, develop restoration goals and objectives, and identify key restoration opportunities. Princeton Hydro participated in data collection and analysis, conceptual restoration designs, and preparation of the USACE Environmental Assessment for the Hudson River Habitat Restoration Ecosystem Restoration Draft Integrated Feasibility Study and Environmental Assessment.

Basic map depicting project sites (Created by Princeton Hydro)The study area includes the Hudson River Valley from the Governor Mario M. Cuomo Bridge downstream to the Troy Lock and Dam upstream. The primary restoration objectives include restoring a mosaic of interconnected, large river habitats and restoring lost connectivity between the Hudson River and adjacent ecosystems.

A total of six sites were evaluated using topographic surveys, installation and monitoring of tide gauges, evaluation of dam and fish barrier infrastructure, and field data collection and analysis to support Evaluation of Planned Wetlands (EPW) and Habitat Suitability Indices (HSI) functional assessment models. Literature reviews were also completed for geotechnical, hazardous toxicity radioactive waste, and aquatic organism passage measures.

Multiple alternatives for each of the six sites were created in addition to the preparation of conceptual designs, quantity take-offs, and cost estimates for construction, monitoring and adaptive management, and long-term operation and maintenance activities.

Princeton Hydro also prepared an environmental assessment in accordance with NEPA standards, addressing all six sites along the Hudson River and its tributaries. This assessment served to characterize existing conditions, environmental impacts of the preferred Proposed Action and No Action Alternatives, and regional cumulative environmental impacts. Our final report was highlighted by USACE at the 2019 Planning Community of Practice (PCoP) national workshop at the Kansas City District as an example of a successfully implemented Ecosystem Restoration Planning Center of Expertise (ECO-PCX) project.

USACE’s specific interest in Hudson River restoration stems from the aforementioned dramatic losses of regional ecosystems, the national significance of those ecosystems, and the apparent and significant opportunity for measurable improvement to the degraded ecological resources in the river basin.

The feasibility study is among the first of several critical steps in restoring the Hudson River’s ecosystem function and dynamic processes, and reestablishing the attributes of a natural, functioning, and self-regulated river system. Stay tuned for more updates on the Hudson River restoration efforts.

Princeton Hydro Team Trained in USACE MII Cost Estimating Software

Congratulations to Amy McNamara and James Hunt of Princeton Hydro who received their certificates of completion for the in-depth training of the October 2017 MCACES (Micro-Computer Aided Cost Estimating System), 2nd Generation (MII) Training Course in Atlanta, Georgia. MCACES is an integrated cost estimating system that meets the U.S. Army Corps of Engineers (USACE) requirements for preparing cost estimates for civil works projects.

This 32-hour course provided an in-depth look at the software application and its components which are used to build detailed construction cost estimates. In a classroom setting, Amy and Jim learned how to prepare and execute computerized cost estimates using parametric worksheets, quantity linking, and assemblies. Our engineering team now has the capability to navigate through the MII software and libraries to create a project, cost items, crews, labor and equipment. Amy and Jim understand how to work with database functions to create site-specific unit prices, modify equipment costs for project specific circumstances, and adjust crew for overtime and shift differential.

Now being used by many of the USACE districts, it will soon be a requirement for all USACE districts to use MII, as well as all architect-engineering (A-E) firms performing design work for the USACE.

“We are looking forward to using the program to help our Federal partners meet their mission objectives,” stated Geoff Goll, President of Princeton Hydro. “The completion of such training efforts continues our commitment to supporting the U.S. Army Corps of Engineers’ efforts in the North Atlantic Division and beyond.”