Sediment Yield Analysis for Powerline, Vineyard Road and Rittenhouse Flood Retarding Structures

About the Program

Category: County Resiliency (Best in Category)

Year: 2017

Sediment volume reduction could potentially reduce dam construction cost for taxpayers in Maricopa County, Arizona. In arid regions, sediment volume is one of the most important engineering parameters for dam design, so an accurate estimate of sediment volume is crucial in mitigating flood risk and reducing maintenance cost for the 22 dams and Flood Retarding Structures (FRS) operated by Flood Control District of Maricopa County (District). An FRS is a type of dam that protects life and property during flood events by capturing and retaining water and releasing it in a safe and controlled manner. The Powerline, Vineyard Road and Rittenhouse FRS are important as they protect approximately 72 square miles of residential, commercial, and agricultural land in Maricopa and Pinal counties from being flooded. This includes key infrastructure such as the CAP canal, Phoenix-Mesa Gateway Airport and the Loop 202 Santan Freeway. The PVR Structures are classified as "high hazard potential structures” where failure or incorrect operation could result in potential loss of human life as well as economic and environmental damages. Because of the earth fissures near Powerline FRS, repair of the PVR Structures is urgent. From 2010 to 2016, the District staff performed a number of sediment yield analyses to attempt to obtain a more accurate estimate of sediment volume. With an improved methodology and better use of technology, the District was able to develop significantly improved estimates for sediment volume in 2016. The final sediment volume was much less than that estimated by the District’s consulting engineer in 2008. The reduction in sediment volume is equivalent to about $8.9 million saving in construction cost. This advancement has helped to save money and allow these dollars to be used to reduce risk and prevent the loss of life and property for other projects.