more precipitation hydrology spring 2013 instructor: eric peterson
TRANSCRIPT
More PrecipitationMore Precipitation
HydrologyHydrology
Spring 2013Spring 2013
Instructor: Eric PetersonInstructor: Eric Peterson
Storm DescriptionStorm Description
• Total amount of Precipitation
• Storm Duration
• Storm Intensity
• Storm Area (least important)
Rainfall MeasurementRainfall 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
Tipping Bucket Gage
NWS-type Calibrated Cylinder
Simple Direct-Read Calibrated
Cylinder
Practice Precipitation CalculationsPractice 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
Time (min)Amount
(mm)
5 1.5
10 5.6
15 13.0
20 5.8
25 2.1
30 9.7
35 4.8
40 1.3
Determining Average Precipitation Determining Average Precipitation over an Areaover 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
Estimating Missing Precipitation DataEstimating Missing Precipitation Data
1. Station-Average Method
2. Normal-Ratio Method
3. Inverse-Distance Weighting