Why are the levees constructed higher than the flood walls?
The levees are designed higher than the required flood elevation to account for settlement within the levees and in the foundation. Over time, the cohesive soils within and beneath the levee will consolidate. The overall estimated settlement is based on the subsurface profiles developed from borings collected in the area and consolidation tests performed on cohesive soils. Calculations for primary settlement and secondary settlement where organic materials were present were calculated along with post-construction settlement of the levee. The overbuild amount varied from location to location due to variable subsurface conditions along the length of the project.
