GEO 361: Hydrology
Precipitation – Areal Estimation (10 pts.) –In-Class Assignment
Directions: Attached is a copy of a basin with 7 gages. Set up a solution using the Isohyetal
Method and the Theissen Polygon Method. Use the following rainfall at each gage:
Gage 1:
Gage 2:
Gage 3:
Gage 4:
Gage 5:
Gage 6:
Gage 7:
.45 inches
.52 inches
.53 inches
.55 inches
.62 inches
.63 inches
.70 inches
Graduate Students: Compute the precipitation for the watershed using the arithmetic mean, the
Theissen polygon method, and the isohyetal method. (15 points)
GEO 361 Hydrology
Spring 2011
Estimating Missing Precipitation:
10 pts.
The figure below shows the location of 11 precipitation gages in a research watershed.
Measurements are missing at gage F for a rain storm during which the amounts shown in the
following table were measured at the other gages. How would you estimate the value at gage F?
Gage
A
B
C
D
E
F
G
H
I
J
K
Distance
from gage F
(km)
5.13
4.43
2.93
3.36
6.63
0.00
2.13
6.10
4.95
4.40
5.93
Average
Annual Precip.
(mm)
1373
1452
1404
1433
1665
1137
1235
1114
1101
1086
1010
Measured
Storm Precip.
(mm)
14.4
12.2
11.6
14.8
13.3
12.3
11.5
11.6
11.2
9.7
Monthly Rainfall Data - Bloomington, IL
2000-2001
January
February
March
April
May
June
July
August
September
October
November
December
January
February
March
April
May
June
July
August
September
October
November
December
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2001
2001
2001
2001
2001
2001
2001
2001
2001
2001
2001
2001
Rainfall
(in)
1.45
1.55
2.4
2.82
4.34
5.51
3.08
4.37
2.52
3.86
3.56
2.1
2.85
4.05
1.59
3.81
5.79
2.91
2.47
3.3
2.91
6.32
2.72
1.83
Rank
Return
Period Probability
Month