Case Study

Balancing Green & Grey Infrastructure Investment in the City of Atlanta

The City engaged Optimatics and Stantec Consulting to developed optimised Long-Term Control Plans (LTCPs) for three of their sewersheds with an emphasis on sustainable stormwater management practices.


Related Topics

Stormwater Management

Green vs. Grey Infrastructure

The City of Atlanta Department of Watershed Management (DWM) is one of the largest utilities in the country, servicing 1.2 million customers daily. DWM places strong emphasis on sustainable stormwater management practices and utilises green infrastructure throughout its networks.


Prior to the optimisation study, DWM identified a range of potential projects in the North Avenue, Clear Creek, and Intrenchment Creek basins to improve hydraulic performance and water quality. The projects involved grey (pipes, tanks etc.) and green infrastructure projects (rain gardens, swales etc.). Having identified these projects, DWM needed to determine which were the most effective to meet performance goals.


Using the OptimizerTM platform, the project team was able to develop a multi-objective optimisation framework where three separate objectives could be utilised simultaneously:

  1. Project Costs
  2. Hydraulic Performance (CSOs, flooding, freeboard)
  3. Triple Bottom Line (TBL) Co-Benefits (social, environmental etc.)

The incorporation of the TBL objective allowed for the green infrastructure projects to be more fairly weighted in the optimisation and is more beneficial than grey infrastructure.

The Optimizer software allowed the Department of Watershed Management to identify the best solutions that aligned with the City of Atlanta ‘One Water’ Vision.

-City of Atlanta Commissioner, Mikita Browning


The project was able to produce hybrid LTCP solutions that cost $65M less than previously proposed grey-only solutions while achieving the same level of hydraulic performance. The proposed solution also scored well for the monetised TBL objective.

The success of the optimisation effort can be contributed to the following:

  • Produced LTCP solutions that saved significant capital costs for DWM and provided benefits to the environment and community through the incorporation of green infrastructure projects.
  • Established a repeatable framework that can be used by the City of Atlanta or other municipalities to incorporate TBL benefits into collection system optimisations.
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