Council weighs detention, culvert and upstream options to reduce West Main flash flooding

Councilmembers discussed multiple engineering options on Sept. 2, 2025, to reduce recurring flash flooding and short-duration road closures at West Main near Timan. Staff described five potential approaches ranging from a roughly $25,000 excavation to enlarge storage at a low point to upstream detention, developer-participation in enlarging a detention basin, culvert enlargement, and future work tied to dredging Lions Lake.

Staff said street crews had closed the section of West Main about five times this year for short periods — typically 20 minutes to an hour — after intense rains, and that some flooding events resolve before crews can arrive. One near-term option (Site 1) would increase storage at a low-lying wetlands mitigation area; an estimated construction cost to create that detention was about $25,000, but the area is within previously recorded wetlands mitigation tied to the Walmart project and would likely require U.S. Army Corps of Engineers permission, removal of roughly 60 trees and tree-replacement that staff estimated could cost between $20,000 and $60,000.

Staff said a second, upstream option (Site 2) adjacent to a playground would avoid the Walmart mitigation area and possibly require fewer permits, but would provide roughly half the additional storage of Site 1 and could require relocating or removing the playground. A third option involves cooperating with a private developer at Bernard and North Park to route runoff into the developer's detention basin and enlarge it; staff said that approach could yield five to ten times the storage available at the low-lying Site 1.

Councilmembers also discussed increasing culvert capacity under Main Street — current small culverts on West Main were described in workshop remarks as roughly 60-inch pipes, while the culvert under the railroad was described as an 8-by-10-foot box — and noted that increasing conveyance at the Main/Timan inlet could reduce street ponding without tree removal. Staff said culvert enlargement would likely be less expensive than tree-removal and mitigation under Site 1 but did not provide a firm estimate and committed to analyze costs.

No funding decision was made. Staff said they will return with cost comparisons, permitting requirements (including Corps permission where wetlands mitigation is implicated), and recommended sequencing for short-term conveyance fixes versus longer-term upstream detention projects. One councilmember summarized the urgency: “Doing nothing is, to me, not an option,” and urged staff to provide a cost analysis that includes the option of increasing culvert capacity to move water away faster.