Blue Earth County holds preliminary hearing on County Ditch 63; engineers and DNR favor storage option

Blue Earth County on Jan. 28 held a preliminary hearing on proposed improvements to County Ditch (CD) 63 in Decoria Township, where engineers recommended replacing failing tile and adding a storage basin to reduce downstream erosion and water‑quality impacts.

At the hearing, Blue Earth County Drainage staff said notices were mailed Jan. 14 and that the county received a Minnesota Department of Natural Resources (DNR) advisory report on Jan. 24. ISG engineers presented a preliminary survey report dated Nov. 8, 2024, describing a watershed of roughly 1,300 acres that drains to a private waterway and then to the Cobb River about 1.6 miles downstream. Engineers reported failing tile, shallow cover depths and sections with cracked, misaligned pipe.

The engineer’s report presented two options. Option 1 would replace and enlarge the mainline and branches without storage; Option 2 includes the same tile work plus a roughly 2.58‑acre downstream water‑storage area with bermed containment and controlled culvert outlets. ISG staff said the storage option reduces modeled peak‑flow changes for several storm events and helps settle sediment and nutrients; the DNR advisory said it preferred the storage alternative because it lessens hydrologic and geomorphologic impacts on downstream public waters and fish habitat.

Engineers reported existing branch and mainline drainage coefficients generally below the industry standard of 0.5 inches per day, noted shallow cover depths in much of the system, and described the proposed design to meet a 0.5 in/day coefficient and a minimum 4 feet of cover (with most of the proposed system at about 5 feet). ISG presented drone and televising imagery showing severe erosion at the outlet, cracked or misaligned concrete tile in places, and debris buildup in branch lines. ISG estimated separable maintenance (repair in kind) at $1,450,000; the full improvement cost, including storage, at $2,650,000; and a net additional cost of $1,190,000 to upgrade capacity and depth as proposed.

The DNR advisory asked the county for additional hydraulic data to evaluate outlet adequacy, including a detailed hydraulic/hydrologic model, cross sections downstream of the outlet and drone data if available. DNR staff noted the receiving Cobb River is impaired for aquatic life and recreation and recommended that the drainage authority provide the meeting minutes, findings, viewers’ report and any final orders to DNR Region 4 when available. The advisory also said Option 1 would require a public waters work permit and that the storage option may avoid that permit if landowner agreements and project updates are provided.

ISG staff said they will refine modeling (including requests to test making Branch 6 a continuous 24‑inch tile), seek landowner agreements for potential storage locations, and prepare a detailed survey and viewers’ report before a final hearing probably later in the year. The county received no public comments during the allotted public‑comment period at the hearing.

The board voted to accept the jurisdictional documents and the preliminary engineer’s report into the record and, later in the meeting, moved to approve the draft findings and order and to appoint viewers and direct the engineer to prepare the detailed survey report. Both motions passed by voice vote.

Engineers and county staff said next steps include more detailed hydraulic analyses, continued landowner coordination on any storage basin and preparation of the viewers’ report and final engineering report for a subsequent hearing.