Committee asks public works to map West Lots stormwater projects and report low-cost resilience options

The committee discussed MB 10, a referral asking administration to integrate underground cisterns in the West Lots. Public Works staff advised the committee that cisterns would require deep excavation, dewatering and substantial infrastructure to collect, store and treat urban runoff, and that in many cases cisterns are not cost-effective compared with other blue-green infrastructure solutions.

Rodney Knowles, assistant director for Public Works, said the department's blue-green master-plan work favors permeable pavement, suspended pavement systems with sub-surface voids, and targeted French-drain-style collection in east-of-island locations where groundwater conditions allow more percolation. He warned that in some locations French drains become less effective as sea level rises and can exacerbate sunny-day flooding if not carefully designed.

Commissioners asked for a clearer picture of stormwater master-plan projects in the West Lots and whether near-term, lower-cost options exist to reduce flooding risk while larger neighborhood projects are planned. Staff agreed to return with a mapping of stormwater master-plan projects, an inventory of critical-needs projects in the West Lots area and a prioritized list of lower-cost interventions (permeable pavement sections, suspended-pavement voids, bioswales or modular rain gardens) with order-of-magnitude costs and potential funding sources.

The committee directed Public Works to consult funding options, including resilience grants and utility-rate options, and to return with a neighborhood-level project list to help prioritize work for the FY capital program.