CIVL253 -HYDROLOGY
SUGGESTED EXERCISES (Infiltration)
1.
The data given below were obtained in a concentric ring infiltrometer experiment on a
rice paddy soil during the dry season in Thailand. Water was maintained at a depth of
1.5 cm inside both the inside ring and in the buffer ring. The inside ring had an
internal diameter of 26 cm. Based on the experimental data, perform the following
tasks:
(a)
Determine the infiltration capacity for the time interval in the experiment.
(b)
Plot the infiltration capacity versus time.
(c)
Find the optimal parameter values in Horton's infiltration equation.
(d)
Find the optimal parameter values in Philip's infiltration equation.
(e)
Find the optimal parameter values in the Green-Ampt infiltration equation.
Elapsed
Time
(min)
Vol. of
H2O added
since
start (cc)
Vol. of H2O
added since
start (cc)
Elapsed
Time
(min)
0
0
20
681
1
63
30
852
2
120
60
1153
5
269
90
1298
10
436
120
1440
2. Assuming AMC II condition, apply SCS method (a) to compute the runoff volume (in
km3) from a 180-mm rainfall on a 610-hectare watershed that has hydrologic soil groups
that are 40 percent group A, 40 percent group B, and 20 percent group C interspersed
throughout the watershed. The land use is 90 percent residential area that is 30 percent
impervious, and 10 percent paved roads with curbs; and (b) to determine the runoff
volume (in km3) for the same watershed and same rainfall before development occurred?
Than land use prior to development was pasture and range land in poor condition.
3. Determine the direct runoff hydrograph, the -index, and the rainfall excess hyetograph
for the storm given below. The watershed area is 18.21 km2.
Time (hr)
Inc. Rainfall (mm)
Instant. Discharge (m3/s)
Time (hr)
Inc. Rainfall (mm)
Instant. Discharge (m3/s)
0
4.6
0.71
4.5
29.1
0.5
10.7
0.76
5.0
23.4
1.0
5.3
1.08
5.5
18.5
1.5
4.1
3.1
6.0
13.2
2.0
8.8
6.5
9.1
2.5
18.5
7.0
6.4
3.0
26.9
7.5
5.5
3.5
30.0
8.0
4.5
4.0
27.4
4. For a watershed having CN = 75, compute the cumulative excess rainfall vs. time and the
excess rainfall hyetograph for the following rainfall event.
Time (min)
Inc. Rainfall (mm)
Time (hr)
Inc. Rainfall (mm)
10
2.7
100
20.0
20
3.1
110
10.6
30
3.6
120
7.5
40
4.2
130
4.9
50
4.4
140
4.3
60
5.7
150
3.6
70
7.8
160
3.2
80
13.0
170
3.0
90
36.0
180
2.5
5. Using the values in table (in lecture notes) containing Green-Ampt infiltration parameters
determine points on the infiltration rate curve for sand, loam, and clay from time to 0 to 4
hours, at 0.5hr increments. Plot and compare these curves. Assume an initial effective
saturation of 30 percent in each soil and continuous ponding.