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Design Rainfall Distributions Based on NOAA Atlas 14

Design Rainfall Distributions Based on NOAA Atlas 14. General Considerations. Standard NRCS rainfall distributions were developed between 1960 and 1985. NRCS is adopting NOAA Atlas 14 in the states where it is applicable. Will a new set of rainfall distributions be required ?

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Design Rainfall Distributions Based on NOAA Atlas 14

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  1. Design Rainfall Distributions Based on NOAA Atlas 14

  2. General Considerations • Standard NRCS rainfall distributions were developed between 1960 and 1985. • NRCS is adopting NOAA Atlas 14 in the states where it is applicable. • Will a new set of rainfall distributions be required ? • If so, how to develop and apply them ? March 2009

  3. Standard Rainfall Distributions March 2009

  4. Geographic Application March 2009

  5. Steps in developing a distribution • Determine ratios of x hour / 24 hour rainfall. • Place the rainfall ratio for the shortest duration in the center of the distribution. • Symmetrically place each larger duration to include the shorter durations. March 2009

  6. 0.7 6 hr Example of a Nested Distribution 0.6 3 hr March 2009

  7. NOAA Atlas 14 web site • Download rainfall frequency data at: • http://hdsc.nws.noaa.gov/ March 2009

  8. Select State March 2009

  9. Selected Ohio March 2009

  10. Selected Columbus Ohio March 2009

  11. NOAA 14 Rainfall Ratios March 2009

  12. Symmetrical Distribution March 2009

  13. Compare to Type II March 2009

  14. Where Type II and Type III compare with NOAA-derived distribution, 25-yr rainfall • Purple: Type II • Pink: Type III • Green: both March 2009

  15. Points used to represent Maryland Counties March 2009

  16. March 2009

  17. March 2009

  18. Future Directions Develop software to easily use the data. • Use GIS data layers to derive site-specific rainfall data for hydrologic modeling. March 2009

  19. March 2009

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