The U.S. Army Corps of Engineers, Omaha District continues to rebuild the Union Dike levee breach near Valley, Nebraska.
The repairs are temporary, but will address a 500-foot section of breach caused by recent flooding in the area, and will serve to prevent future flood waters from entering the affected area.
“This is a temporary levee to restore some level of protection in the event of any water until a later date when a levee can be rebuilt to certain standards with proper cohesive and random fill material,” said Dustin Davis, civil engineer, USACE-Omaha “That way, you can have proper testing requirements to prove it’s been compacted properly.”
The levee breach is being filled with sand and crushed concrete procured roughly half-a-mile from the breach. From there, the raw materials are hauled to the work site and bumped before being pushed by a bulldozer into the breach.
One of the challenges with this project has been obtaining materials. Initially, the Omaha District specified 40,000 tons of riprap which would be used to protect shorelines against erosion. However, local quarries do not have enough material available so construction efforts have had to make due with alternative materials.
Another complication is that engineers are filling a scour hole. Scour holes are created when swiftly moving water carries away sediment, thereby compromising the integrity of a structure. However, it is not yet known if the scour hole caused the Union Dike levee failure.
“A lot of the times we don’t get into the weeds of how stuff happened. It’s more of what do we have and how do we fix it,” Davis said.
The initial levee breach was filled in a day on the landward side, and now sand is being pushed from the landward side to riverside. Once the scour hole is filled it will provide a base the actual levee will be rebuilt on top of.
Filling the scour hole can be challenging. The hole is underwater meaning there is not a very good way to estimate how much material will be needed to fill it.
“We do a pre-construction topographic survey to figure out the elevations of the levee itself before we start placing material. We also do a post-construction topographic survey to find the final elevation and based on the volume between those two surveys and the density and type of materials we’re able to determine quantities,” Davis said. “For this project since we’re putting a lot of it underwater we’re counting truckloads of sand to identify the exact quantity of sand that’s been placed to date.”
Since March 25, approximately 500 trucks with an average payload of 36 tons have made the trip to the levee construction site.
The Union Dike contract is for $959,500 and was awarded to Pruss Excavation on March 21. Construction began quickly with Pruss Excavation establishing haul routes, doing a pre-construction survey and grading the same afternoon. The hauling of sand began the next day March 22. Construction is expected to conclude March 27.
“For this emergency contract everybody has come together as a team and worked well together. This is a good start for a lot of work upcoming,” said Davis.