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Middleton staff say Madison projects and updated rainfall estimates could raise peak flows; group agrees to proceed with remap using updated 100‑year rainfall
Summary
City of Middleton staff and their consultant reviewed modeling showing that near‑term drainage projects in Madison and updated rainfall estimates raise peak flows for smaller, more frequent storms and can raise the 100‑year water surface in upstream ponds. The group recommended modest model updates and to proceed with floodplain remapping using the higher 100‑year rainfall estimate while pursuing collaboration with Madison.
City of Middleton staff and their consultant briefed members on August 1 on how planned and recent drainage projects in the City of Madison, together with more recent rainfall estimates, could change flood risk in Middleton the South Fork/Pheasant Branch watershed.
The presenter, a project consultant working under Middleton's remapping contract, summarized City of Madison projects including the Swallowtail Park work and the Pheasant Branch Enhancement Project. He said Madison has designed those projects and obtained funding and permits, and that, in model runs, they increase peak discharge for smaller storms while having little or no effect on the largest floods. The presenter said that in a sensitivity test substituting a higher 100‑year rainfall estimate the model showed roughly a 28 percent increase in peak flow at the city boundary and a rise of more than a foot at South Pond in an extreme simulation.
"If there is more rain, you know, there's more flooding downstream," the presenter said…
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