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.

NJDEP Releases Updated Guidance for Harmful Algal Blooms

Last summer, 39 of New Jersey’s lakes were plagued with toxic algae outbreaks, also known as harmful algae blooms or HABs, causing major water quality degradation, beach closures and health advisories. In response, the NJDEP implemented a unified statewide approach to addressing HABs in freshwater recreational waters and sources of drinking water, and protecting the public from risks associated with exposure to cyanobacteria.

Last week, NJDEP announced a new component to its statewide Cyanobacterial HAB Response Strategy: a color-coded health alert index that provides precise recreational use recommendations for impacted waterbodies based on levels of cyanobacteria and/or cyanotoxins present. The index has six tiers – NONE, WATCH, ALERT, ADVISORY, WARNING, and DANGER – each providing recommendations on the specific activities that should or should not be pursued based on water monitoring results.

“Princeton Hydro is proud to be one of the contributing factors in the development of the Updated Guidance for HABs,” said said Dr. Fred Lubnow, Director of Aquatic Resources for Princeton Hydro. “We feel this updated protocol will provide the necessary and objective information for State and local organizations to make informed and rational decisions, based on sound and scientifically-based data, on how to deal with HABs in a recreational setting.

Princeton Hydro and Clean Water Consulting are the technical advisers for the New Jersey Lake Group, who have met a number of times over the last 8 to 9 months to discuss the State’s guidance on dealing with HABs.  In late 2019, on behalf of the New Jersey Lake Group, Princeton Hydro and Clean Water Consulting developed a White Paper providing recommended changes for consideration to NJDEP’s Recreational Response Strategy to HABs.

“I’m proud to say that many of the provided recommendations were integrated into NJDEP’s Updated Guidance for HABs,” explained Dr. Lubnow.

WATCH
(Suspected or confirmed HAB with potential for allergenic and irritative health effects)
This warning will be posted when HAB cell counts exceed 20,000. In this scenario, public beaches remain open, but the index instructs the public to use caution, provides information on the potential less serious health effects, and allows for more informed decision-making.

ALERT
(Confirmed HAB that requires greater observation due to increasing potential for toxin production)
This warning indicates a public bathing beach closure only and is posted when a HAB has been confirmed with cell counts between 40,000 and 80,000 and no known toxins above the public threshold. Beaches remain open (dependent upon local health authority) and monitoring for future toxin production should be increased.

ADVISORY
(Confirmed HAB with moderate risk of adverse health effects and increased potential for toxins above public health thresholds)
Signs will be posted for this warning level when cell counts exceed 80,000 or when toxin levels exceed 3 micrograms per milliliter of microcystins. Public bathing beaches will be closed, but the waterbody will remain accessible to some “secondary contact” activities, like boating.

WARNING and DANGER
(Confirmed HAB with high risk of adverse health effects due to high toxin levels)
and (Confirmed HAB with very high risk of adverse health effects due to high toxin levels)
These tiers are designed to alert the public to the presence of HABs that are producing very high levels of toxins which justify additional caution. In some instances, the entire waterbody may be closed for all public use. New Jersey has experienced approximately 12 “warning level” HAB events over the last 3 years; monitoring has never indicated a “danger level” HAB event.

According to their press release, NJDEP is committed to working with local officials to implement the index and get signage posted at lakes throughout the state as soon as possible.

In order to create the health index, NJDEP scientists carefully reviewed HABs data collected over the last three years by Lake Hopatcong Commission, Lake Hopatcong Foundation, Princeton Hydro, and other sources. The tiered warning system will enable lake communities, residents and visitors to make more individualized decisions about what risks they are willing to take and what activities they feel comfortable engaging in at the various levels of HABs.

In the coming days, the NJDEP’s Harmful Algal Bloom website will be updated to include the new health index and accompanying signage, relevant monitoring data, and other information for each of the impacted bodies of water, as well as an updated HAB Monitoring and Response Strategy. For now, you can read the full press release and additional information here: https://www.nj.gov/dep/newsrel/2020/20_0023.htm.

To learn more about HABs, check out our recent blog:

Identifying, Understanding and Addressing Harmful Algae Blooms

Our 2020 Earth Day Photo Contest Winner!

In honor of Earth Day, Princeton Hydro held its annual Photo Contest with the theme “Human Impact” for its employees. We’d like to thank everyone who submitted photos this year. Overall, we received 27 gorgeous submissions from our staff.

All photos were rated on the following criteria by three volunteer judges: Danielle Odom, Lucy Aquilino, and Amanda Brooks (see bios below).

  • Technical Quality (30%)
  • Originality (30%)
  • Artistic Merit (40%)
THE WINNER OF THE PRINCETON HYDRO 2020 EARTH DAY PHOTO CONTEST IS…

“Welcome Home” – Although its a local and small impact, I intentionally leave dead wood in sunny places on my property. This ensures that I always have an Eastern Fence Lizard like this big female to greet me when I come home. Southern New Jersey. By Clay Emerson.

Scroll to the bottom to see a gallery of runner-up photos.

ABOUT THE JUDGES:
DANIELLE ODOM

Danielle is a Staff Scientist II at the Academy of Natural Sciences of Drexel University. Her career is dedicated to watershed monitoring research and her responsibilities include both field and laboratory work. She has specialized in studying biological indicators as a parameter to track stream health via macroinvertebrate taxonomy; in particular identifying members of the non-biting midge family Chironomidae. Once an experiential outdoor educator, she taught nature photography to middle school students as a pathway to understanding different perspectives and the impact of humans on the environment, a la Ansel Adams.

Lucy Aquilino

Lucy is a retired Parole officer and amateur photographer. A mom of 2, she loves taking nature photos and going on adventures with her kids.

Amanda Brooks

Amanda is a nature enthusiast who loves taking long walks in the woods with her camera and notepad. With her degree in Environmental Studies and English and her background in the arts, she is always looking for creative ways to capture the beauty of nature to inspire its protection. She currently resides in Burlington, Vermont and works as a tree-monger at Gardener’s Supply Company. You can check out more of her work on her Facebook page. 

Check out the photos from last year’s Earth Day photo contest here:

Our 2019 Earth Day Photo Contest Winner!