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rate of the S hydrograph. (b) Determine the 2 h unit hydrograph from the S hydrograph; be careful
to scale the intensity over 2 h to ensure a volume of 1 cm. (c) Calculate the peak storm runoff
(in m
3
s
−
1
) resulting from three successive 2 h periods of rainfall producing volumes of 0.4, 1.0
and 1.6 cm of runoff, respectively.
Storm runoff (m
3
s
−
1
)
Storm runoff (m
3
s
−
1
)
Time (h)
Time (h)
0
0
8
19.70
1
4.01
9
15.76
2
15.26
10
11.62
3
36.55
11
8.30
4
45.40
12
5.30
5
40.48
13
3.33
6
31.99
14
1.56
7
24.40
15
0
12.3
Below isa6hunit hydrograph (UH) from a drainage area of 875 km
2
on Goose Creek, near
Leesburg, Virginia.
Time (h)
UH (m
3
s
−
1
)
Time (h)
UH (m
3
s
−
1
)
Time (h)
UH (m
3
s
−
1
)
0
0.00
28
27.34
54
1.00
2
0.13
30
13.34
56
0.87
4
0.40
32
10.00
58
0.67
6
1.80
34
7.34
60
0.60
8
7.34
36
5.34
62
0.53
10
17.34
38
5.27
64
0.47
12
29.34
40
4.20
66
0.40
14
44.68
42
3.47
68
0.33
16
66.69
44
2.80
70
0.27
18
104.03
46
2.20
72
0.20
20
113.37
48
1.80
74
0.13
22
112.04
50
1.47
76
0.07
24
81.36
52
1.20
78
0
26
59.35
(a) Check what the unit volume is of this unit hydrograph from the (smoothed) steady equilibrium
flow rate of the S hydrograph. (b) Find the peak flow (in m
3
s
−
1
) resulting from three successive 4 h
periods
of
rainfall
producing
volumes
of
5.1,
30.5,
16.5
mm
of
runoff,
respectively
(ignore
base
flow).
(The
above
UH
is
derived
from
data
in
Corps
of
Engineers,
(1963).)
12.4
Consider the following excess rainfall time sequence on a hypothetical catchment:
x
1
=
0.5 cm
h
−
1
from 1400 to 1500;
x
2
=
1.5 cm h
−
1
from 1500 to 1600;
x
3
=
0.75 cm h
−
1
from 1600 to 1700.
This rainfall produced the following storm runoff hydrograph.
