City engineers say state requires new dam studies before Lake Mitchell drawdown can proceed

Mitchell city and consulting engineers told the City Council on Tuesday that the state dam‑safety regulator now expects additional studies before it will approve plans for the Lake Mitchell drawdown and spillway work.

The city’s consultant, Eric Lund of Barr Engineering, said the South Dakota Department of Agriculture and Natural Resources (DANR) has asked for a probable maximum flood/inflow design flood analysis and a spillway capacity and freeboard analysis. "A probable maximum flood or a PMF is the largest hypothetical flood that could occur," Lund said, adding that the requested studies are desktop hydrologic and hydraulic analyses rather than field work.

Those studies, Lund said, are likely to take about three to six months to complete and could cost roughly $100,000 to $200,000. He said the worst‑case outcome of the review could require changes to the dam or spillway — which would add scope, cost or schedule risk to the lake project — while a best‑case result would clear the way to proceed next year.

The engineering presentation also summarized the city’s permitting work: the Army Corps of Engineers nationwide permit application is in review, and state permitting would follow. Lund said the studies were not flagged in earlier, multi‑year conversations with the state and that dam‑safety requirements appear to be evolving.

Council members and the public asked technical and process questions about alternatives (breaching the earth embankment versus the concrete spillway), the permit schedule, who would perform the studies, and whether additional studies could be requested later. Lund and city staff said the state could require the same studies at any time, whether the project moves forward now or in the future.

After extended public comment and questions, the council did not vote on the lake project itself. Instead members said they wanted staff to return with a checklist of outstanding permit and study requirements and competitive cost proposals from engineering firms so the council could decide on whether and when to authorize the additional work. "I would suggest that we give Joe and his team time to answer them," Mayor Hansen said during the discussion.

The council also reviewed project budget status: city staff reported the overall lake project budget includes contingency and that some design spending is paused pending the path forward. Staff said the project has contingency that could be drawn for studies if council chooses; alternately council could authorize a supplemental if it prefers to use other funds.

What happens next: city staff will gather the requested checklist and several engineering cost proposals for the hydrologic/hydraulic analyses and return them for council review and potential contract authorization before the studies begin.