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# Assignment

Problem 1
The names and locations of the rain gauge stations with their mean annual precipitation are as
given in the table below. Calculate average precipitation of the catchment area by Isohyetal
method.
Name of
Station

Latitude
Degrees

Minutes

Longitude
Degrees
Minutes

Mean Annual
Precipitation
(in)

A
B
C
D
E
F
G
H
I
J
K
L

16
16
14
17
17
17
14
16
15
17
15
16

03
35
58
25
27
10
53
25
15
26
45
26

103
104
102
104
101
104
103
101
104
102
102
102

04
44
07
50
44
09
29
08
53
46
02
51

39.85
56.58
45.73
85.12
47.51
70.59
52.67
50.83
60.57
56.22
41.50
46.81

Latitude and Longitude of the Catchment Area are 140 30 to 180 30 and 1010 00 to 1040
00, respectively.
Problem 2
Assuming the rain falling vertically, express the catch of a gauge inclined 15 from the vertical
as a percentage of the catch of a gauge installed vertically.
Problem 3
A 3-hour storm occurred at a place and the precipitation in the neighboring rain-gage stations P,
Q and R were measured as 3.8, 4.1 and 4.5 cm respectively. The precipitation in the neighboring
station S could not be measured since the rain gauge was damaged. The normal annual
precipitation in the four stations P, Q, R and S were 45, 48, 53 and 50 cm, respectively. Estimate
the storm precipitation at station S.
Problem 4
In a catchment one precipitation station A, was inoperative for part of a month during which
storm occurred. The respective storm totals at three surrounding stations 1, 2 and 3 are 35, 40
and 30 mm, respectively. The normal annual precipitations at A, 1, 2 & 3 are respectively 985,
1125, 940 and 1210 mm. Estimate the storm precipitation for Station A.

Problem 5
The average annual precipitation for the four sub-basins constituting a large river basin is 58, 67,
85 and 80 cm. The sub-basin areas are 900, 690, 1050 and 1650 km, respectively. What is the
average annual precipitation for the basin as a whole?
Problem 6
The annual precipitation at station A and the
15 surrounding stations are given in the Table 3.19 given below:
a. Determine the consistency of the record at station A.

average

precipitation

at

## b. In which year, there is a regime change indicated?

Table 3.19 Data Table
Year

1971
1972
1973
1974
1975
1976
1977
1978
1979
1980

Annual Precipitation
Station A
15 Station
(cm)
Average (cm)

50.5
90.0
16.0
21.5
50.5
62.5
69.5
36.0
42.0
42.0

71.5
57.0
27.5
25.0
60.0
22.0
55.0
57.0
36.5
19.5

Year

1981
1982
1983
1984
1985
1986
1987
1988
1989
1990

Annual Precipitation
Station A
15 Station
(cm)
Average (cm)

36.0
42.0
18.0
30.0
54.0
48.0
12.0
36.0
42.0
36.0

27.5
60.5
55.0
38.5
38.5
47.5
49.5
24.0
44.0
60.5

Problem 7
The Table 3.20 given below gives the annual rainfall at a station A and the average annual
rainfall of 10 stations in the vicinity for a period of 17 years. It is suspected that there has been a
change in the location of the rain gauge at Station A during the period of this record. Determine
the year when this change occurred and the corrected rain gauge readings prior to this year.

## Table 3.20 Rainfall Data

Rainfall
Year

Station A
(mm)

Average
Annual
Rainfall of 10
Stations (mm)

1931
1932
1933
1934
1935
1936
1937
1938
1939
1940

505
900
60
215
505
625
695
360
420
360

615
570
275
250
605
220
550
570
365
275

Year

Rainfall
Average
Station A
Annual
(mm)
Rainfall of 10
Stations (mm)

1941
1942
1943
1944
1945
1946
1947

420
180
300
540
480
120
360

605
550
385
385
475
495
240

Problem 8
Point rainfalls due to a storm at several rain-gauge stations in a basin are shown in Fig. 3.16.
Determine the mean areal depth of rainfall over the basin.

8 cm

6 cm
zone
Area(km)
I
410
II
900
III
2850
IV
1750
V
720
VI
550
Area of the Basin = 7180 km

8 cm
zone I

N (9.2)

zone VI

O (7.4 cm)

D (9.2)
G (8.5)

A (8.6)

L (5.2)

C (10.8)
M (5.6)
H (10.5)
E (13.8)

K (7.8)

B (7.6)
F (10.4)

I (11.2)
J (9.5)
zone II

10 cm
zone V
zone IV

zone III
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