S Curves
From Mays, 2011, Ground and Surface Water Hydrology
Example
The 1- hr unit hydrograph for a watershed is
given below. Determine the 2 hr unit
hydrograph.
Time ( hr)
Unit hydrograph ( cfs)
1
10
2
100
3
200
4
150
5
100
6
50
S Curve to Develop 2 hr unit
hydrograph
Time (hr) Unit hydrograph (cfs)
1
10
2
100
10
3
200
100
10
4
150
200
100
5
100
150
200
6
50
100
150
7
0
50
100
8
0
50
9
0
10
11
12
13
14 700
S
10
100
200
150
100
50
0
10
100
200
150
100
50
0
10
100
200
150
100
50
0
Diff
10
110
310
460
560
610
610
610
610
610
610
610
10
100
200
150
100
50
0
600
10
110
310
460
560
610
610
610
610
610
610
610
2 hr Unit Hydrograph
10
5 700
110
55
300
150 600
350
175
250
125 500
150
75
400
50
25
0
0 300
200
100
0
0
2
4
6
8
0
2
4
6
8
250
500
200
400
300
150
200
100
100
50
0
0
2
4
6
8
10
12
0
Problem 8.5.3
Suppose the 4-hr unit hydrograph for a
watershed is
Time (hr)
0
2
4
6
8
10
12
14
Unit hydrograph (m3/s/10 mm)
0
15
45
65
50
25
10
0
a) Determine the 2-hr unit hydrograph
b) A design storm has 1 cm/hr in first 2 hr and
0.5 cm/hr in the second 2 hr. Baseflow = 10
m3/s. Calculate the total runoff hydrograph
Problem 8.2.4.
Time
4:00
4:30
5:00
5:30
6:00
6:30
7:00
7:30
8:00
8:30
9:00
9:30
10:00
10:30
Cum.
Rain
Instantaneous
Runoff
0
0
30
0.3
80
4.2
90
11.3
95
13
127
34
130
45.3
132
21.2
9.3
4.8
2.5
1.4
0.8
0
Problem 8.2.4.
Time
4:00
4:30
5:00
5:30
6:00
6:30
7:00
7:30
8:00
8:30
9:00
9:30
10:00
10:30
Cum.
Rain
Instantaneous Inc Vol
Inc Depth
Runoff
(m3)
(mm)
0
0
30
0.3
270
0.032
80
4.2
4050
0.482
90
11.3
13950
1.661
95
13
21870
2.604
127
34
42300
5.036
130
45.3
71370
8.496
132
21.2
59850
7.125
9.3
27450
3.268
4.8
12690
1.511
2.5
6570
0.782
1.4
3510
0.418
0.8
1980
0.236
0
720
0.086
Instantaneous Runoff (m^3/s)
50
45
40
35
30
25
20
15
10
31.74
5
0
3:36
4:48
6:00
7:12
8:24
9:36
10:48
Determining the  index and Excess
Rainfall Hyetograph
Phi . DT
26.75
60
Excess
50
Incremental Rainfall
Rainfall (mm) (mm)
0
40
30
3.246674 3.246674
50 23.246674 23.24667
10 -16.753326 30
0
5 -21.753326
0
32
5.246674 5.246674
20
3 -23.753326
0
2 -24.753326
0
10
Sum positive
31.74
0
3:30
4:00
4:30
5:00
5:30
6:00
6:30
7:00
7:30