Evanston presents citywide stormwater master plan, highlights model and targeted capital projects

City officials and consultants on May 12 described a newly completed stormwater master plan they say will guide investments to reduce street flooding and basement backups across Evanston.

Bridget Nash, senior project manager for the city, introduced the report and said the study uses a detailed hydrologic and hydraulic model of the city's combined and separate sewer networks to locate weaknesses and prioritize improvements. "The model is now used as a valuable and powerful tool in evaluating system performance under current and future needs," Nash said.

Hay & Associates project manager Jeff Wickenkamp said the model represents the city at a neighborhood scale: about 9,500 catchments (roughly two-thirds to three-quarters of an acre each) and some 12,000 pipe segments, which the consultants estimate represent more than 200 miles of sewer conduits. The model was calibrated with flow-monitoring data gathered in summer 2021, including two rain gauges and 23 flow monitors, Wickenkamp said. That calibration, he said, allowed the team to assess three core questions: surcharge risk (water level in sewer relative to basement elevations), surface flooding extents, and the potential to reduce combined-sewer overflows as projects are built.

City staff and consultants grouped recommendations into three buckets. Regulatory suggestions include tightening detention requirements for smaller buildings and more robust private-property plumbing compliance at point of sale. Private-system recommendations focus on ways property owners can reduce flood risk. Public-system recommendations include capital improvements, improved system monitoring and pilot projects for surface-flooding and green-infrastructure concepts. The plan also identifies concept projects: an example green-infrastructure concept for Mason Park, permeable pavers installed last year on Main Street, permeable play surfaces at Independence and Larimer Parks, and a surface-flooding concept for the city's southwest where historic North Shore Channel grades limit overland flow.

Nash said the model already informed the 2024 and 2025 capital improvement program. She noted three alley-improvement locations and a storm-sewer extension of roughly 2,340 feet are in the 2025 CIP, and work linked to street resurfacing on McDaniel Avenue will include about 330 feet of new storm sewer, according to the presentation. Nash also outlined a plan to install level meters on Church Street this season to monitor water elevations and to use those sensor data to investigate reported flooding and to maintain the model's calibration. The city intends to update the model every two to three years as sewer construction or other changes occur.

Council members asked clarifying questions about how the model maps to capital projects and how regulatory changes would be enforced. The presentation concluded with staff offering to provide additional, project-level information as proposed projects move into design and permitting.

The stormwater master plan presentation was informational; no council vote or formal direction was recorded at the meeting. City staff indicated the plan will continue to guide CIP decisions and regulatory discussions going forward.