Missouri River At Florence Bend Bedrock Excavation

On the Missouri River near Omaha, NE a bedrock outcrop, known as the Florence rock shelf or reef, was blasted during the original navigation channel construction to create the authorized navigation channel depth. Removal included a minimal provision for future degradation and was limited to the 300 foot navigation channel width. The Florence Reef elevation does not remain constant but fluctuates up and down along its length.

Downstream of the I-680 bridge, the Missouri River navigation channel contacts the bedrock outcrop. Missouri River degradation, accelerated by several extreme floods over the last 12 years, has resulted in insufficient navigation channel dimensions at several locations within the area between river mile (RM) 626.4 to 625.3. Material removal was deemed necessary to restore the minimum navigation channel dimensions and remove hazards to river navigation. Maintenance crews from the Omaha District performed partial removal of pinnacles in the fall of 2021, but the scope of the project required development of a contract to address the issue fully.

The project is novel in that dredging in the main channel is an atypical activity for the Omaha District and it is rare that bedrock is encountered in the predominately sand bed.

Design activities associated with the project included geological study, multi-beam hydrologic surveys, bedload sediment sampling, and hydraulic modeling.

Under a compressed design schedule, construction plans and specifications were developed in consultation with other USACE districts to appropriately address the unique construction project of mechanical excavation of bedrock from floating plant.

The project was awarded in April 2022, with construction underway and completion scheduled for the Fall of 2022.