UNCERTAINTY AND RISK ANALYSES FOR FEMA ALLUVIAL-FAN METHOD

Alluvial fans along mountain bases present challenges in the design of hydraulic structures and highway crossings and for flood insurance investigations. The Federal Emergency Management Agency (FEMA) alluvial-fan method is an approximate method, leaving it subject to uncertainties. The authors of this paper apply Rosenblueth's point-estimate to the FEMA alluvial fan method to calculate the mean and standard deviation for the 100-year discharge at any point on the fan and the mean and standard deviation for the fan arc width. The mean and standard deviation for the 100-year discharge are used to derive the risk that the 100-year discharge will exceed the discharge capacity of hydraulic structures on the fan. The mean and standard deviation for the fan arc width are used to approximate the risk that a given location on the fan is within the hazard flood zone. The HEC-1 rainfall-runoff computer model is employed to compute inputs to the FEMA method. An alluvial fan in north Scottsdale, Arizona, is used to demonstrate the proposed uncertainty and risk analyses.

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  • English

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  • Accession Number: 00726079
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Sep 19 1996 12:00AM