US Army Corps of Engineers
St. Paul District Website Website

Mississippi River Lock and Dam 1, Ambursen Dam Downstream Repair

Published Feb. 26, 2015
Updated: April 16, 2020

The purpose of this project is to re-establish armor downstream of the concrete apron and prevent further scour.


Lock and Dam 1 is located on the Minneapolis, Minnesota side of the Mississippi River.


The existing rock protection consists of grouted derrick stone. This grout has failed resulting in the derrick stone being broken up and washed downstream, exposing bedding material and risking failure of the wooden piles and sheet pile located underneath the existing concrete apron.

The St. Paul District performed an analysis in fiscal year 2013 and determined that placing bedding and rip rap in the scoured area from the concrete apron extending 150 feet downstream is the most efficient and effective solution. Construction involves a removal of the remaining grouted rip rap and derrick stone, excavating excess material immediately downstream of the concrete apron, and using the material to smooth out the downstream topography and placing bedding and rip rap in to the scour/repair area.


The St. Paul District awarded the initial construction contract in January 2015. Persistent high water (flow > 6k cubic feet per second) has prevented the contractor from accessing the area safely since the award.

In November 2018, site surveys were conducted to evaluate the conditions as a result of the continued high flows since contract award. Surveys indicated that there has been some additional deposition in the area but the scour has not progressed.

The original repair method and material quantities are unchanged; however, the additional deposition in the scour will have to be excavated as part of the construction.

The contract was terminated in July 2019, and plans and specifications are being prepared for re-solicitation in spring 2020 in preparation for a summer 2020 construction contract award.


Congress authorized the project as part of the River and Harbor Act approved July 3, 1930.


FY 2019:
Analysis Design (labor)                                    $37,600
Contract Termination                                      $52,500

FY 2020:
E&D/S&A                                                         $121,100
Contract (estimate)                                     $2,512,000