Connecting blue-green infrastructure elements to reduce combined sewer overflows

Area of Science:

• Environmental Engineering
• Urban Hydrology
• Water Resource Management

Background:

• Combined Sewer Overflows (CSOs) are a major source of urban water pollution.
• Blue-Green Infrastructure (BGI) offers a solution by managing stormwater.
• Previous research often focused on individual BGI types, not their real-world combinations.

Purpose of the Study:

• To systematically assess the CSO mitigation potential of various BGI combinations.
• To evaluate the impact of different BGI elements, implementation rates, and routing schemes.
• To quantify the effectiveness of BGI in reducing CSO discharge and frequency.

Main Methods:

• Evaluated 60 BGI combinations using four elements (bioretention, permeable pavement, green roofs, detention ponds).
• Assessed four implementation rates (25-100% of catchment area) and four runoff routing schemes.
• Utilized hydrological modeling to quantify CSO volume reduction and frequency.

Main Results:

• BGI combinations substantially reduce CSO volumes, but detention ponds can increase CSO frequency.
• The performance of BGI combinations differs from the sum of individual BGI effects.
• Larger implementation areas are not always more cost-effective; optimal strategy depends on objectives.

Conclusions:

• BGI combinations are crucial for CSO mitigation, with detention ponds playing a key role.
• BGI type, implementation area, and runoff routing are critical factors in CSO reduction.
• A systematic approach is needed to develop tailored BGI strategies for urban catchments.