### Magnitude and frequency of floods in the United States, part 13. Snake River basin

By: C. A. ThomasH. C. BroomJ. E. Cummans

                            https://doi.org/10.3133/wsp1688

#### Links

-                                                                                                                             Document:                                                                                                                                                                                                                                                  **Report**                                                                                                     (pdf)                                                                                                                                     
- Plates:                               - **Plate 1**                            (pdf)  Map of physiographic regions of Snake River basin
  - **Plate 2**                            (pdf)  Precipitation index map of the Snake River basin
  - **Plate 3**                            (pdf)  Map of Snake River basin showing location of gaging stations with 5 or more years of annual flood record
  - **Plate 4**                            (pdf)  Map of Snake River basin showing flood regions
  - **Plate 5**                            (pdf)  Map of Snake River basin showing geographic factors 
- NGMDB Index Page:  **National Geologic Map Database Index Page**
- Download citation as:  RIS                         |                         Dublin                            Core

#### Abstract

The magnitude of a flood of any selected frequency up to 50 years for any site on any stream in the Snake River basin can be determined by methods outlined in this report, with some limitations. The methods are not applicable for regulated streams, for drainage basins smaller than 10 or larger than 5,000 square miles, for streams fed by large springs, or for streams that have flow characteristics materially different from the regional pattern. The magnitude of a flood for a selected frequency at a given site is determined by using the appropriate composite frequency curve and the mean annual flood for the given site. The mean annual flood is computed from either a formula or a nomograph in which drainage area, mean annual precipitation, and a geographic factor are used as independent variables. The standard error of estimate for the computation of mean annual floods is plus 17 percent and minus 15 percent.

Nine flood-frequency regions (A-I) are defined. In all except regions B and I, frequency relations vary with the mean altitude of the basin as well as with the geographic location; therefore, families of curves are required for 7 of the 9 flood-frequency regions.

The report includes a brief description of the physiography and climate of the Snake River basin to explain the reason for the large variation in mean annual floods, which range from zero to about 27 cubic feet per second per square mile.

Composite frequency curves and formulas for computing mean annual floods are based on all suitable flood data collected in the Snake River basin. Tables show the data used to derive the formula. Following the analysis of data are station descriptions and lists of peak stages and discharges for 295 gaging stations at which 5 or more years of annual flood records were collected pr'or to Sept. 30, 1957. Many flood peak data are not usable in defining the frequency curves and deriving the formula because of large diversions and regulation upstream from the gaging stations. 

#### Study Area

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