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National Stream & Aquatic Ecology Center

National Stream & Aquatic Ecology Center

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Updated: 03/23/2020

Flood Potential

Greater insight into the expected magnitudes and spatial variability of floods is needed to more effectively manage our stream valley 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 substitution to predict expected large flood magnitudes 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 quantifies 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 flood variability in both space and time. Additional indices were developed, which together facilitate the comparison of flooding characteristics across regions and continents, to help understand and communicate about flood hazards.

This methodology was developed to be used in companion with existing flood-frequency methods, and 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?
  • Are floods increasing in magnitude over time?

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

Map of the western United States of America showing the extent of currently-available analysis.

Overall Summary

Southern Rocky Mountains

West Coast

 

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