Purpose
Phase 1 of this project is focused on addressing the dangerous outdraft condition at the upstream end of the lock. Phase 1 includes hydraulic data collection and modeling alternative design options identified in collaboration with the nagivation industry to improve present conditions. This phase will conclude with an Enginering Research and Development Center (ERDC) Ship Simulation exercise in the first and second quarter of fiscal year 2024. This will allow industry pilots to test the navigation conditions for each alternative design, allowing the St. Paul District to make the best informed decision on the approach to Phase 2 implementation, which include plans, specifications and construction.
Location
Lock and Dam 7
330178 Highway 61 La Crescent, MN 55947-4304
Description
In 2017, a hydraulic study was launched to identify potential causes of the increased outdraft and to investigate and implement measures to alleviate the condition. Flow measurements collected over the last 30 years indicate a significant shift in flows just upstream of Lock and Dam 7 with nearly 20% more flow coming through the existing navigation channel which must then exit through the dam, exacerbating the outdraft condition.
A two-dimensional hydraulic model was developed to analyze existing flow conditions and assess potential mitigation measures. The upper approach to Lock and Dam 7 is uniquely narrow and shallow therefore many common river training structures are not feasible within the area.
Several combinations of rock structures and dredging scenarios were modeled, but only one showed promise. A rock weir extending off of the river wall was constructed to a depth of 7 feet below low control pool in late 2018. The weir was expected to reduce velocities throughout the approach and therefore the impact of the outdraft on navigation. The weir was extended further upstream by 260 feet in 2020 following a request by the navigation industry.
Status
Navigation industry expressed concerns with the outdraft and rock wier at Lock and Dam 7 at the Mississippi Managers Meeting in February 2023, classifying it for the first time as a life safety issue. In April, St. Paul District engaged industry partners to collaborate in meetings bi-quarterly to get their input for the solution. A design charette was conducted with navigation partners and regional experts in June 2023 to outline the near, short and long-term options available and the associated timelines. It was determined that a future budget package will need to be submitted for a long-term structural solution.
Authority
Congress authorized the Upper Mississippi River 9-Foot Channel Navigation Project as part of the River and Harbor Act, approved July 3, 1930.
Funding
To date, the project planning and design phase are using 100% federal funds. Design alternatives with positive results documented in the ERDC Ship Simulation final report will be included in the fiscal year 2027 budget submissions to prepare plans and specifications for a construction contract award to address the outdraft condition.