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Older coastal cities such as Boston, New York, and Philadelphia face the risk of untreated sewage inundation during floods. The design of combined sewer systems, coupled with rising sea levels and increased precipitation, exacerbates this issue. According to researchers at Drexel University, this combination could lead to a significant public health crisis.
The team from Drexel University recently published research modeling the potential impact in Camden, New Jersey. They examined the effectiveness of proposed interventions to protect these communities from the adverse effects of climate change and outdated infrastructure.
The Challenge of Combined Sewer Systems
Since 1855, many coastal cities in the United States have relied on combined sewer systems, where stormwater and sewage are collected in the same pipes. Initially, these systems discharged directly into streams and rivers, later redirecting to wastewater treatment facilities. However, these pipes have limited capacity. During heavy rainfall, excess flow overflows into natural water bodies through combined sewer overflows (CSOs).
The Federal Pollution Control and Clean Water Act has mandated upgrades to reduce CSOs, but climate change introduces new challenges. Higher water levels in receiving bodies of water prevent CSO flap gates from opening, causing combined sewage to back up, spilling onto streets and into basements. This issue is worsened by increased rainfall and higher river levels due to climate change.
Innovative Solutions and Future Projections
Drexel University researchers, in collaboration with the Camden County Municipal Utilities Authority (CCMUA), have been exploring potential solutions. Their research, published in the Journal of Water Management Modeling, utilized hydrologic and hydraulic models to simulate flooding and CSOs in Camden’s Cramer Hill section. This area is prone to flooding and is located near the largest CSO point on the east side of the Delaware River.
The models, validated against historical data and actual flood photographs, projected future conditions with up to 30% increased precipitation and 1.8 meters of sea level rise. Results indicated that increased precipitation could lead to overflow discharges 21-66% above current levels, while sea-level rise, though reducing the number of overflow events, increased the duration of flooding.
One proposed solution involves diverting upstream stormwater away from Cramer Hill’s sewer system, known as the “Pennsauken disconnection.” This strategy was found to be beneficial under all future climate scenarios, though challenges remained, especially with sea-level rise increasing flood durations.
Looking Ahead
The research highlights that climate change will intensify combined sewer overflows and complicate discharge processes into nearby bodies of water. With 40 million people living in areas served by combined sewer systems, addressing this issue is critical. Drexel’s team plans to continue refining their model, incorporating more data on water flow and surface flooding, and evaluating additional infrastructure interventions.