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.

Green Infrastructure and Stormwater Utilities: Solutions to NJ’s Environmental Issues

Flooding, runoff, and storm surges, OH MY!

With increases in each of these occurring now, the imposition of green infrastructure and a stormwater utility fee are viable solutions to reducing their impacts. Plus, with the passing of the S-1073/A2694 bill in early 2019, the introduction of a stormwater utility became legal in New Jersey, making it the 41st state to do so.

On June 19, 2019, The Watershed Institute in Pennington, NJ held the “New Jersey Green Infrastructure & Stormwater Utilities Symposium” to address the environmental problems New Jersey faces and present solutions, including the stormwater utility. The event was geared for municipal officials, engineers, nonprofit leaders, and other interested parties, with an agenda full of expert speakers sharing insights and ideas on topics like the science of stormwater, New Jersey’s proposed stormwater rule changes, why green infrastructure and a stormwater utility fee matter, and possibilities for how to move New Jersey forward.

So, What is Green Infrastructure?

Brian Friedlich, the first presenter and a project manager for Kleinfelder, relayed that according to NJDEP, green infrastructure consists of “methods of stormwater management that reduce stormwater volume, flow, or characteristics by allowing the stormwater to infiltrate, be treated by vegetation or by soils, or be stored for use.” He also explained that green infrastructure can improve the environment and communities by providing community engagement, greening communities, addressing flooding, improving water quality by reducing CSOs, harvesting rainwater, increasing habitat for wildlife, and increasing property values.

After Brian’s presentation, a founding Principal of Princeton Hydro, Dr. Stephen Souza, now CEO of Clean Waters Consulting, urged that we should “turn down the volume,” when it comes to stormwater runoff. He explained that it is not enough to just manage peak flow of stormwater; we must also work to lower the volume of off-site stormwater discharge. So, how can you and your municipality do this? He offered six principles to designing successful green infrastructure projects:

  1. Treat stormwater as a resource
  2. Don’t make stormwater management an afterthought
  3. Attack the cause not the symptoms
  4. Turn your watershed inside out
  5. Think small to achieve big results
  6. Use nature as your model

Not only is successful implementation of green infrastructure important, but communal understanding of it may be more so. That is why Princeton Hydro partnered with New Jersey Future, Clark Caton Hintz, Rutgers Cooperative Extension Water Resources Program, FZ Creative, and municipal stakeholders to launch the New Jersey Green Infrastructure Municipal Toolkit. Filled with helpful information about green infrastructure, this free resource is extremely useful for gaining communal understanding, getting started, implementing nature-based stormwater solutions, and sustaining your program.

What is Stormwater and Why Should Municipalities Require a Utility Fee for It?

Before we get into why it is imperative for New Jersey municipalities to implement a stormwater utility fee, it is important to understand just what stormwater is, what it does, and how it affects New Jersey residents.

The name is pretty intuitive: stormwater is the water that comes from precipitation, whether that be rain, snow, or ice melt. With increasing levels of water from climate change impacts (i.e. storm surge, increased rainfall, sea level rise), stormwater management has become an issue for states all across the U.S., whether it’s an over abundance or lack thereof.

So, what’s happening in New Jersey? The stormwater infrastructure that is currently in place (storm drains, sewer piping, etc.) is aging and unable to effectively handle the amount of runoff that has been flowing through the region in recent years. This is causing increased nutrient runoff and flooding all over the state. And, with increasing global temperatures, this trend is likely to continue.

To combat these issues, New Jersey passed the S-1073/A2694 bill in January 2019, authorizing counties and municipalities, either separately or in combination with other municipalities, to begin implementing a stormwater utility fee to New Jersey residents.

The law itself states:

“Every sewerage authority is hereby authorized to charge and collect rents, rates, fees, or other charges for direct or indirect use or services of its stormwater management system. The stormwater service charges may be charged to and collected from the owner or occupant, or both, of any real property. The owner of any real property shall be liable for and shall pay the stormwater service charges to the sewerage authority at the time when and place where these charges are due and payable. The rents, rates, fees, and charges shall be determined in a manner consistent with the stormwater utility guidance manual created by the Department of Environmental Protection pursuant to section 24 of P.L.

Any stormwater service charge imposed pursuant to subsection a. of this section shall be calculated in a manner consistent with the guidance provided in the stormwater utility guidance manual created by the Department of Environmental Protection pursuant to section 24 of P.L.”

Essentially, this fee charges a chosen type of property owner within a given municipality or region a certain amount of money for the impervious area (mainly artificial structures like asphalt, concrete, stone, rooftops, etc. that water can’t seep through) they have on their property. Just how much that fee is and whether or not there’s a limit on the chargeable impermeable area are dependent on the government agency.

Since the impervious area blocks water from seeping into the ground, it becomes runoff and ends up in the stormwater drain. And, since New Jersey’s systems are growing old and less efficient, it makes sense to implement a fee for their use. Historically, general taxpayer dollars or legislative appropriations have been used to fund updates to aging infrastructure. Implementing a utility fee will create a consistent funding source to update and expand the current aging infrastructure so that flooding will occur less.

Other states, like neighboring Pennsylvania, have been proactive in addressing these impacts by implementing a stormwater utility fee. And, in Maryland, the state implemented a watershed restoration program and MS4 efforts that require stormwater utility fees. These initiatives have generated a job-creating industry boom that benefits engineers, contractors, and local DPWs. At the same time, Maryland’s program is improving the water quality in the Chesapeake Bay, and stimulating the tourism and the crabbing/fishing industry.

In relation to how urban cities are affected by stormwater, John Miller, the FEMA Mitigation Liaison, shared this helpful resource, “The Growing Threat of Urban Flooding: A National Challenge” during the symposium. It addresses the extent and consequences of urban flooding in the U.S., while exploring actions that can be taken to mitigate future flooding. Amongst other recommendations made, the research group encouraged Congress and state officials to “develop appropriate mechanisms at the federal, state, and local level to fund necessary repairs, operations, and upgrades of current stormwater and urban flood-related infrastructure.”

A stormwater utility should not only be reviewed in the context of cost, since it meets all three elements of a triple-bottom line: social, environmental, and financial. Other considerations are the fact that allowing stormwater utilities in New Jersey will create jobs, help reduce flood impacts, enhance water quality, improve our fisheries, and preserve our water-based tourism economy.

When it comes to green infrastructure, Princeton Hydro has been a leader in innovative, cost-effective, and environmentally sound stormwater management systems since its inception. Long before the term “green infrastructure” was part of the design community’s lexicon, the firm’s engineers were integrating nature-based stormwater management systems to fulfill such diverse objectives as flood control, water quality protection, and pollutant load reduction. And, Princeton Hydro has developed regional nonpoint source pollutant budgets for over 100 waterways. The preparation of stormwater management plans and design of stormwater management systems for pollutant reduction is an integral part of many of the firm’s projects. So, we are major proponents of implementing stormwater utilities and green infrastructure into our everyday lives.

Do you have questions regarding green infrastructure or stormwater utilities? Contact us here.

 

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.