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 Longitude Mean Annual

Precipitation (in)

Degrees Minutes Degrees Minutes

A 16 03 103 04 39.85

B 16 35 104 44 56.58

C 14 58 102 07 45.73

D 17 25 104 50 85.12

E 17 27 101 44 47.51

F 17 10 104 09 70.59

G 14 53 103 29 52.67

H 16 25 101 08 50.83

I 15 15 104 53 60.57

J 17 26 102 46 56.22

K 15 45 102 02 41.50

L 16 26 102 51 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 average precipitation at 15 surrounding stations are given in the Table 3.19 given below:

a. Determine the consistency of the record at station A.

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

Table 3.19 Data Table

Year

Annual Precipitation

Year

Annual Precipitation

Station A (cm)

15 Station Average (cm)

Station A (cm)

15 Station Average (cm)

1971 50.5 71.5 1981 36.0 27.5

1972 90.0 57.0 1982 42.0 60.5

1973 16.0 27.5 1983 18.0 55.0

1974 21.5 25.0 1984 30.0 38.5

1975 50.5 60.0 1985 54.0 38.5

1976 62.5 22.0 1986 48.0 47.5

1977 69.5 55.0 1987 12.0 49.5

1978 36.0 57.0 1988 36.0 24.0

1979 42.0 36.5 1989 42.0 44.0

1980 42.0 19.5 1990 36.0 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

Year

Rainfall

Year

Rainfall

Station A (mm)

Average Annual

Rainfall of 10 Stations (mm)

Station A (mm)

Average Annual

Rainfall of 10 Stations (mm)

1931 505 615 1941 420 605

1932 900 570 1942 180 550

1933 60 275 1943 300 385

1934 215 250 1944 540 385

1935 505 605 1945 480 475

1936 625 220 1946 120 495

1937 695 550 1947 360 240

1938 360 570

1939 420 365

1940 360 275

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.

G (8.5)

D (9.2)

K (7.8)

J (9.5)

H (10.5)

I (11.2)

E (13.8)

C (10.8)

F (10.4)

B (7.6)

A (8.6)

N (9.2)

O (7.4 cm)

L (5.2)

M (5.6)

zone I

zone II

zone IIIzone IV

zone V

zone VI

zone Area(km)

I 410

II 900

III 2850

IV 1750

V 720

VI 550

Area of the Basin = 7180 km

8 cm

8 cm 6 cm

10 cm

Figure 3.16 Isohyetal Map