Public works outlines stormwater program: inspections, off-site options and basin maintenance study

Wyatt Thompson, interim public works director, told the City Commission on April 20 that Manhattan’s stormwater program is organized into four buckets — neighborhood drainage systems, detention systems, water‑quality controls and floodplain management — and that staff are moving toward two short‑term deliverables: an inspections program for privately maintained detention basins and development of an alternative off‑site post‑construction BMP (best management practice) compliance program.

Thompson said the city adopted updated stormwater management criteria in 2023 and is now collecting feedback to amend and clarify certain submittal requirements. He described the neighborhood drainage work (inlets, pipes, swales and easements), the detention program (dry and wet ponds and underground storage) and the water‑quality program required by the municipal separate storm sewer system (MS4) permit administered through the Kansas Department of Health and Environment (KDHE).

Bill Heatherman, stormwater compliance engineer, described enforcement tools and inspection practices for construction‑site erosion controls. “We strive to get voluntary compliance and have a good relationship with the builders,” Heatherman said, adding that the city can issue notices of violation, abate noncompliant controls and, in extreme cases, seek stop‑work orders or municipal court action but that those remedies are time‑consuming.

Thompson said detention is required for sites of 0.4 acres or greater when there is an increase in impervious area; post‑construction water‑quality BMPs are required for developments of 1 acre or more (or parcels that are part of a common plan of development). Staff reported there are roughly 107 privately maintained detention basins and 17 underground systems within the city. Thompson said staff plan to inspect privately maintained basins beginning this fall to create an inventory, document maintenance needs and identify basins that may require city assistance or capital repairs.

On water quality, staff described a proposed alternative off‑site compliance program modeled loosely on Wichita’s program. Under the model, developers could voluntarily enroll and pay a fee based on treated impervious area; the city would use those fees to fund agricultural conservation practices (cover crops, no‑till, other best practices) in targeted upstream areas and take credit for pollutant reductions to satisfy KDHE water‑quality obligations. Thompson and Bill Heatherman said KDHE had been consulted informally and gave positive feedback on the concept; staff plan to return with a detailed proposal for commission consideration later this year.

Commissioners asked about enforcement strength when builders do not comply with temporary erosion controls; Heatherman reiterated inspection cadence and existing ordinance authority, and said the city can abate noncompliance and put costs on tax rolls if necessary. Commissioners also questioned funding and scope. Thompson said the stormwater utility funds program operations and capital planning but does not cover every development obligation; staff noted the city’s stormwater operating budget is roughly $4 million per year.

Staff outlined next steps: finalize recommendations from the detention‑basin maintenance study begun in 2023, launch basin inspections this fall, advance the alternative off‑site water‑quality program for KDHE review and amend the city’s stormwater management criteria and Manhattan Development Code for clarity. Commissioners voiced general support for staff to continue developing the alternative off‑site water‑quality program and to proceed with inspections and follow‑up reporting to the commission.

Ending: Staff will return with proposed ordinance language, an off‑site program proposal for KDHE approval, and a basin‑inspection report that lays out costed options for corrections and maintenance responsibilities.