Performance Evaluation of Articulated Contrete Matting (ACM) Spillway at Lake Odessa, Iowa

Use of Articulated Concrete Matting (ACM) for overflow spillways has great ability to resist high overflow velocities, yet use of ACM for this purpose is rare at the Corps of Engineers. This presentation draws attention to the importance of ACM spillway design to the HH&C community and how it performed at Lake Odessa, Iowa during the Flood of 2008. Many Environmental Management Projects are protected from flooding by perimeter levees. Typically these levees offer 10-year or 25-year protection and are frequently overtopped causing major damage to levees that can be very expensive to repair following each flood. Levee breaches may also produce adverse impacts on the ecosystems that they are intended to protect. The addition of spillways on perimeter levees can drastically reduce or eliminate overtopping damage to levees. From experience in the Rock Island District, head differences of less than one foot between the exterior and interior water levels will result in insignificant levee damage during overtopping events. A simple but effective spreadsheet technique was used to size the spillways according to this design assumption. The final spillway design made use of articulated concrete matting (ACM) to resist anticipated shear forces versus the more conventional techniques of riprap or concrete spillways. Construction of the spillway was completed in the winter of 2006 by the Corps of Engineers, making the Lake Odessa spillway the first substantial ACM spillway project by the Corps of Engineers. The flood of 2008 overtopped the ACM spillway twice allowing Rock Island District and Resource Agency personnel to monitor water levels. This paper evaluates the performance of the ACM spillway at Lake Odessa and presents lessons learned from the Flood of 2008.