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storm flood relief

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Cohocksink/Northern Liberties Storm Flood Relief: Big Investments to Help Our Neighborhoods

For our final Infrastructure Week post, we are looking at a massive, multi-year project that will help reduce flooding related to heavy rains in several neighborhoods. Like many other cities, Philadelphia is dealing with a sewer system designed for a time when there were far fewer hard surfaces like streets, parking lots and buildings.

Because those surfaces don’t absorb rain, the water becomes stormwater runoff, which can overwhelm sewers, leading to localized flooding and combined sewer overflows. While the City is relying on Green Stormwater Infrastructure investments made through the Green City, Clean Waters program to deal with this challenge, those green tools are more effective when we also improve our traditional sewer system.

A good example of an investment in our existing system that will enhance Green City, Clean Waters projects is the Cohocksink Storm Flood Relief project, also called the Northern Liberties SFR. The project is named after the Cohocksink Creek, which once flowed through Kensington and Northern Liberties and emptied into the Delaware River not far from where SugarHouse Casino stands today.

Like many small streams in Philadelphia, the Cohocksink was covered over and integrated into the sewer system in the mid to late 1800s.
Today, the Cohocksink sewer system must manage stormwater drainage from more than 1,000 acres of urban land. 

To get the inside scoop on the Cohocksink improvements, we put a few questions to project manager Bill Dobbins, an engineer who has worked with Philadelphia Water since 2001.

Improvements to Address Northern Liberties Flooding

Northern Liberties flooding that occured after a July 9 downpour. Credit: Northern Liberties Neighbors Association.
Northern Liberties flooding that occurred after a July 9 downpour. Credit: Northern Liberties Neighbors Association.

After yet another heavy rainstorm last week, a section of Northern Liberties experienced localized flooding as result of an overwhelmed stormwater system.

This area contains the historic Cohocksink Creek and is the focus of a long-term infrastructure improvement project. Traditional sewer expansion and green stormwater tools will improve the capacity of the local system while reducing the amount of water entering sewers.

Philadelphia Water is aware of last week's flooding and on-going issues, and we're working with the community to address immediate concerns as we implement a plan to improve conditions in the long haul.
You can see a summary of plans to address flooding in the vicinity of Wildey and N. American streets here and here.

Impacted residents are also encouraged to attend a community meeting on the Northern Liberties Storm Flood Relief Program. Philadelphia Water representatives will discuss flood reduction efforts at the South Kensington Neighborhood Association,1301 N. 2nd St., on Tuesday, July 14 at 6:30 p.m.

Stress on the Sewers: Is June Philly's New Monsoon?

The July 9 storm dumped nearly an inch of rain in just under 10 minutes—the heaviest of the month so far—and came at a time when the Delaware River was at its highest tide level.

It’s been a rather wet summer so far, and that means additional stress for stormwater infrastructure. After a historically dry May, June made up for it with a vengeance. Only two years have seen a wetter June in the city, according to records dating to 1872.

The wettest June ever was in 2013, followed by 1938 and 2015 with 8.88 inches. The National Weather Service lists June’s rain average as 3.43 inches.

It’s all part of a trend that has seen six of the rainiest Junes EVER occur in the city in just the last dozen years:

June 2013: 10.36 (1st)

June 2015: 8.88 (3rd)

June 2003: 8.08 (4th)

June 2006: 7.95 (6th)

Is it too soon to talk about storm flood relief?

Well this is certainly a topic that is fresh in everyone’s minds as recent extreme rains have left basements flooded, cars wrecked, roads closed, and our Water Works temporarily out of commission. These events are becoming more frequent as what used to be known as “100-year storms” occur once or twice each decade now. In this region, PWD plays an important role in planning for consequences of global climate change and mitigating the effects of these weather events.

Our primary method of handling this has been to reduce the amount of stormwater run-off that rushes directly into our streams and rivers by investing $40 to $50 million each year to create more acreage to soak that rain into the ground water. We’re also investing $30 million in infrastructure improvements every year to enhance our ability to collect and divert stormwater. Over the next several years we are studying potentially $1 billion in system improvements through our Green City, Clean Waters program. For homeowners, PWD has provided nearly $1.7 million since 2005 to install basement back-up protection devices at 455 homes in the city.

PWD and our partner city agencies are also coordinating response and recovery with other city, state, and federal agencies to provide advanced warning forecasts in advance of large storms. We’re creating tidal and neighborhood flooding projections and vulnerability analyses, revising FEMA flood map, projecting climate change impacts, installing signage in vulnerable areas, reviewing zoning and building codes, and meeting with communities to help guide them through these changes.

PWD has always been forward looking and has anticipated the challenges and opportunities that Philadelphia has faced over the decades. Storm flood relief is a challenge that is only going to get more severe over the next several decades. We continue to focus on the issue as we have for the past several years.

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