US Army Corps of Engineers
St. Paul District Website


Mississippi River Lock and Dam 1, Ambursen Dam Downstream Repair

Published Feb. 26, 2015
Updated: Sept. 20, 2019

Lock and Dam 1 is located on the Minneapolis side of the Mississippi River. The purpose of this project is to re-establish armor downstream of the concrete apron and prevent further erosion.

The existing rock protection consists of grouted derrick stone. This stone bedding has 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 U.S. Army Corps of Engineers performed a cursory analysis in fiscal year 2013 and determined placing riprap 200 feet from the concrete apron downstream would be the most efficient and effective solution. Construction involves a contractor removing grouted riprap, excavating excess material immediately downstream of the concrete apron, and using the material to smooth out the downstream topography.

The Corps awarded the initial construction contract in January 2015. Persistent high water has prevented the contractor from accessing the area safely for the past four years. Contract was terminated in July 2019.

In November 2018, we conducted site surveys to assess the project conditions as a result of the continued high flows. Site conditions indicate that there has been some additional deposition in the area, which will result in additional excavation as part of the repair.

Evaluating options for expediting the construction process by purchasing and staging materials so that when flow conditions are safe for work, the construction contractor can move quickly without having to source materials from distant quarries.


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


Project design and construction costs are 100 percent federal.

Project costs to date                                       $538,388
Estimate contract cost                                 $2,500,000