13 Quaternary Geology and Geomorphology

Tuesday, 1 May 2001
1:10 PM - 5:00 PM

CITIZENS GROUP WORKS WITH GEOMORPHOLOGIST TO ASSESS NEIGHBORHOOD FLASH FLOOD HAZARDS

Paper number: 13-2
Program: Technical Sessions
Time: 3:15 PM – 3:30 PM

Authors

  • John Cobourn Presenting Author
    Univ of Nevada Cooperative Extension, Incline Village, NV
  • Steve Lewis
    Univ of Nevada Cooperative Extension, Incline Village, NV
  • Kyle House
    Univ of Nevada, Reno, Reno, NV

Abstract

A group of Western Nevada citizens formed a Flood Safety Coalition after their community experienced four non-lethal flash floods in the early 1990s. Though their alluvial fan community was urbanizing rapidly, the record of past flash flood events was less than 20 years old. While some citizens urged that structural flood control measures be taken, others asked how the cost/benefit ratio could be determined. Were the recent floods relatively "large" events, or were they small "warning floods", indicating that a "100 year flood" could be catastrophic for the community?

The coalition obtained grant funding and hired a geomorphologist to begin assessing the extent of flood hazardous areas on a number of alluvial fans in the sprawling desert community. The coalition also sought county government support for these studies, and encouraged the county to include a discussion of flash flood hazards in its Master Plan Update.

The geologic evaluation of alluvial fan flood hazards on lower Buckbrush Wash indicated that the active fan apex was lower on the fan surface than previously thought. This finding was of particular interest, because the active fan apex is below several homes previously mapped as being in a "Zone A" floodzone. No surficial geological evidence was found to indicate that these homes were actually in a "significant flood hazard area". As a result, the coalition is now pursuing non-structural rather than structural flood management options for this wash.