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More Precipitation

More Precipitation. Hydrology Spring 2011 Instructor: Eric Peterson. Storm Description. Total amount of Precipitation Storm Duration Storm Intensity Storm Area (least important). Rainfall Measurement. Measured as depth of rain per area of surface

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More Precipitation

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  1. More Precipitation Hydrology Spring 2011 Instructor: Eric Peterson

  2. Storm Description • Total amount of Precipitation • Storm Duration • Storm Intensity • Storm Area (least important)

  3. Rainfall Measurement • Measured as depth of rain per area of surface • 1 in of rain would cover a given area to a depth of 1 in • Typically measured ~3 ft above ground in area sheltered from wind, but unaffected by surrounding structures and vegetation • Measurement Devices • Calibrated Cylinder, Tipping Bucket, Scale

  4. Simple Direct-Read Calibrated Cylinder Tipping Bucket Gage NWS-type Calibrated Cylinder

  5. Practice Precipitation Calculations • Distribution of rainfall during a storm on the University of Georgia Whitehall Forest in June, 1990 (Brown, 1993) • Calculate total precipitation • Calculate peak 5 min intensity • Determine duration • Calculate Average Intensity

  6. Determining Average Precipitation over an Area • If rain gages are evenly distributed a simple arithmetic average may be calculated • Thiessen method: essentially a weighted average based on area between gages • Isohyetal method: lines of equal rainfall (isohyets) are drawn on the watershed, then a weighted average is calculated based on the area between lines

  7. Estimating Missing Precipitation Data • Station-Average Method • Normal-Ratio Method • Inverse-Distance Weighting

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