Alluvial Fan Stage 2 Methodology

About the Program

Category: Risk and Emergency Management (Best in Category)

Year: 2016

Many areas in Maricopa County, Arizona have been identified as active alluvial fans by the Federal Emergency Management Agency (FEMA) and local governments. Accurate delineation of active alluvial fans becomes an important task because flooding on active alluvial fans is extremely dangerous. The Flood Control District of Maricopa County (FCD) has successfully developed a Stage 2 alluvial fan delineation methodology that is consistent with FEMA’s nationwide general methodology but adds more geomorphic and engineering details to meet Maricopa County’s physical conditions. The methodology fills the gap between the federal requirements and Maricopa County realities. The methodology is easy to use and is reproducible, which results in more accurate and efficient alluvial fan delineation services to the County. The methodology was successfully applied to two active alluvial fans in Scottsdale and Phoenix in 2014. The results were approved by FEMA in 2015. The impact is huge because the two previously considered active fans are actually inactive fans. Therefore, potentially more than 2,000 home owners will not need to buy flood insurance, saving a total of about $12 million flood insurance cost for the next 10 years. A glossary of terms can be found in the Supplemental Materials section.