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APPROPRIATION / PHASE: General Investigations

BUSINESS PROGRAM: Watershed Planning

AUTHORITY: Section 22, Water Resources Development Act of 1974, as amended

DESCRIPTION: The U.S. Army Corps of Engineers (USACE) and the Philadelphia Water Department (PWD) executed a Planning Assistance to States (PAS) Agreement on September 28, 2011, for USACE to provide technical assistance in support of City efforts to address localized flooding in various Philadelphia neighborhoods. USACE first completed a technical review of hydrologic and hydraulic modeling completed by PWD for the East Germantown neighborhood’s combined sewer system.  In May 2013, the Corps and PWD modified the scope of work to investigate levee construction to protect the Eastwick neighborhood in Southwest Philadelphia, which sustained severe flooding during Hurricane Floyd in 1999 and during approximately ten storms since.

The PAS program, as defined by Section 22 of the Water Resources Development Act of 1974, authorizes the Corps of Engineers to provide technical assistance to States, local governments, and other non-Federal entities.  However the PAS authority does not allow for design or construction assistance, nor does it authorize feasibility investigations.  Opportunities to continue the flood damage reduction project study in Eastwick under the Section 205 authority for Small Flood Damage Reduction Projects are now being explored.  Under this authority, USACE and a non-federal partner could evaluate additional flood damage reduction alternatives, conduct an economic analysis, and formulate an actionable plan to alleviate flood impacts in the Eastwick community.

STATUSUSACE developed a hydraulic model to assess future conditions in the Eastwick neighborhood, with and without a levee project. Model simulations showed that levee construction would protect Eastwick residents from flooding up to and including the 1% annual chance of exceedance (100-year) storm event.  However, levee construction would also encroach on the flood plain and raise water surface elevations both upstream and downstream of the project.  During a 0.2% chance (500-year) event, water levels could rise as much as 1.5 feet at the confluence of Darby and Cobbs Creeks, as a result of levee construction. The Army Corps delivered a final report to PWD describing these findings in December 2014.  The report recommended that additional analysis be conducted to evaluate project alternatives that may provide flood protection without inducing higher water levels elsewhere. Additional alternatives to consider would include: property buyouts; channel modifications; various levee and floodwall alignments; and combinations thereof.

PROJECT GOALS: The purpose of this project is to evaluate the potential for a levee to protect the Eastwick neighborhood.  This evaluation will consider geotechnical, hydrologic, hydraulic and environmental concerns.

PROJECT STATUS: USACE completed hydraulic modeling and delivered a final report to in December 2014. 

CONCLUSION: Further study is needed to evaluate additional alternatives that do not induce water level rise elsewhere in the system. Opportunities to continue the study are now being explored under the Section 205 authority for Small Flood Damage Reduction Projects.

SPONSOR: Philadelphia Water Department

DATE OF PROJECT AGREEMENT: 28 September 2011