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Stormwater master plan proposes $53 million near-term CIP and $40 million future-growth planning; council to review adoption next month
Summary
Marion City's draft stormwater master plan recommends 30 priority areas distilled into 34 recommended projects (22 storm-sewer projects, underground detention, drainageway and basin modifications), proposes a three-tier existing-CIP of roughly $53 million and a separate $40 million future-growth planning bucket, and uses SUDAS design standards (10-year and 100-year events). Staff will return next month with the final report for adoption and financial modeling.
Marion City's stormwater master plan, presented May 19 by stormwater coordinator Steve Cooper and HDR project lead Steph Vay Hogi, lays out a prioritized program of projects to reduce flooding risks and plan for future growth. The plan identifies 30 problematic areas and recommends a mix of projects: 22 storm sewer replacement/construction projects, two underground detention projects, two drainageway projects, two detention-basin outlet modifications, and construction of three new detention basins.
As an example, HDR presented a Wanity Creek project on the city's southeast side near Alexis Lane and Grand Avenue: after alternatives analysis HDR proposed constructing new storm sewer between two detention basins and modifying an outlet structure. HDR estimated that example would proceed in three phases with a combined construction cost of $2.4 million.
To guide implementation, staff proposed a three-tier capital improvements plan for the existing system. Tier 1 projects (the highest priority) total roughly $13 million and should be completed first; tier 2 is also about $13 million and generally addresses localized needs or projects contingent on tier 1 work; tier 3 totals about $27 million and would be pursued later or in coordination with other work such as road reconstruction. Together the existing-system CIP is approximately $53 million. A second, separate CIP for future-growth planning (regional detention and major stream crossings) totals about $40 million and is intended for planning and potential developer participation rather than immediate scheduling.
Councilors pressed staff on who would pay for regional detention and whether developers could buy into regional facilities; Cooper said the city would likely fund initial construction and developers could buy into regional detention as development occurs. Council also asked about the design storm levels: the plan follows Iowa SUDAS standards, Cooper said, designing storm sewers to contain a 10-year event in the pipe and addressing private-property protection for a 100-year event; HDR staff agreed to add typical inch-based descriptions in the public-facing materials (roughly 3.5 inches in 24 hours for a 10-year event and 5—6 inches in 24 hours for a 100-year event, per discussion).
Next steps: staff said the plan will be finalized and brought back to council next month for formal adoption along with the financial modeling and rate/rate-pace options to fund implementation.
