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National Stream & Aquatic Ecology Center

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Updated: 11/04/2019

Flood Potential

Greater insight into the expected magnitudes and spatial variability of floods is needed to more effectively manage our resources and build more sustainable communities. However, our understanding of floods is limited and hazards can be poorly communicated by technical specialists to decision makers and the public.

A new method was developed using a space-for-time (ergodic) substitution to predict expected flood magnitudes at any location (within the analyzed watershed drainage area ranges) given the streamgage record in similarly-responding nearby watersheds. Regressions of record peak discharges using drainage area and additional watershed characteristics Flood damage to a paved road in the forest.were fit across areas with similar flood records, with these areas referred to as zones. Each of these regressions define the expected flood potential for each zone, which provides the expected flood magnitudes. The 90% prediction limit defines the maximum likely flood potential, with discharges above this level being extreme and departure indicating the degree of extremity.

From these zonal regressions, a flood potential index was developed to rank flood hazards between zones, and a variability index was developed to quantify within-zone variability. In combination with a flashiness index, an overall flood hazard index was developed. Additionally, a flood extreme index was developed to rank extreme and other peak flow flood events. These indices facilitates the comparison of flooding characteristics across regions and continents, to help understand and communicate flood hazards.

This methodology assists practitioners with answering such questions as:

  • What large flood magnitudes can be expected at a given ungaged location, for designing infrastructure?
  • How reasonable are the results of regional flood frequency regression equations?
  • Is a flood frequency analysis at a specific streamgage providing reasonable results, or are results biased due to the presence or absence of a large flood?
  • What areas are inherently prone to larger or smaller floods (have a larger or smaller flood potential index)? This helps make more informed decisions regarding:
    • Erosion hazards of stream corridors
    • Inherent risks of stream restoration
    • Risks of wildfire-induced flooding or debris flows on communities
  • Is a specific flood extreme, or rather a typical large flood?
  • Compared to other floods in the area, how extreme is a flood?

The currently-available analysis extent is shown below, followed by summary articles and data, and currently available information:

Map of the United States of America showing the location of the Southern Rocky Mountains analysis extent.

Overall Summary

Southern Rocky Mountains

GIS data:

 

For more information on this method, please contact Steven Yochum, Hydrologist, USDA Forest Service, National Stream and Aquatic Ecology Center.

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