Surface and Sub-surface Hydrology
Q1) Consider the rainfall event having 5-min cumulative rainfall record given below:
a) What is the duration of the entire rainfall event and the corresponding total rainfall amount?
b) Find the rainfall depth hyetograph (in tabular form) with 10-min time interval for the storm event.
c) Find the maximum 10-min and 20-min average rainfall intensities (in mm/hr) for the storm event.
|
Time (min)
|
Cumulative rainfall (mm)
|
|
0
|
0
|
|
5
|
7
|
|
10
|
14
|
|
15
|
23
|
|
20
|
34
|
|
25
|
45
|
|
30
|
58
|
|
35
|
70
|
|
40
|
81
|
|
45
|
91
|
|
50
|
100
|
|
55
|
110
|
|
60
|
119
|
|
65
|
125
|
|
70
|
131
|
|
75
|
136
|
|
80
|
140
|
|
85
|
140
|
Q2) An experimental rectangular plot of 10 km x 12 km has five rain guage stations as shown in the figure below. The storm rainfall and coordinates of the stations are given in the table. Based on the position of the five rain gauges, construct the Thiessen polygon for them and estimate the mean annual rainfall that falls on the plot.
|
Station
|
(x,y)
|
Mean annual rainfall (cm)
|
|
A
|
(1, 3)
|
128
|
|
B
|
(8, 11)
|
114
|
|
C
|
(3, 10)
|
136
|
|
D
|
(5, 8)
|
144
|
|
E
|
(7, 5)
|
109
|
Q3) Consider a 2-hr storm event with a total rainfall amount of 80 mm. the measured direct runoff volume produced by the storm is 40 mm.
a) Determine the decay constant k in Horton's infiltration model knowing that the initial and ultimate infiltration rates are 30 mm/hr and 2 mm/hr, respectively.
b) Use the Horton equation developed in Part (a) to determine the excess rainfall intensity (mm/hr) hyetograph for the following storm event.
|
Time (min)
|
0-10
|
10-20
|
20-30
|
|
Incremental rainfall depth (mm)
|
5
|
20
|
10
|
Q4) Consider the following storm event given below for a small catchment of 120 hectares. For baseflow of 0.05 m3/s:
a) Compute the volume of direct runoff (in mm),
b) Assuming initial losses (abstraction) are 5 mm, determine the value of the Φ-index (in mm/hr)
c) The corresponding effective rainfall intensity hyetograph (in mm/hr)
|
Time (min)
|
Cumulative rainfall (mm)
|
Discharge (m3/s)
|
|
0
|
0
|
0.05
|
|
5
|
5 (initial loss)
|
0.05
|
|
10
|
20
|
0.25
|
|
15
|
35
|
0.65
|
|
20
|
45
|
0.35
|
|
25
|
|
0.15
|
|
30
|
|
0.05
|
Q5) Obtain a Unit Hydrograph for a basin of 273.6 km2 of area using the rainfall and streamflow data tabulated below. Assume baseflow to be 150 m3/s.
|
Time (h)
|
Rainfall (cm)
|
Observed Hydrograph (m3/s)
|
|
0
|
0
|
150 |
|
1
|
0.25
|
150 |
|
2
|
2.75
|
350 |
|
3
|
2.75
|
800 |
|
4
|
0.25
|
1200 |
|
5
|
|
1100 |
|
6
|
|
650 |
|
7
|
|
400 |
|
8
|
|
300 |
|
9
|
|
200 |
|
10
|
|
150 |
|
11
|
|
140 |
Q6) The following table contains the records of rainfall and runoff data of a particular storm event for a watershed with drainage area of 8.4 km2:
a) Determine the maximum rainfall intensity for durations of 30 min, 60 min, and 120 min.
b) Determine the percentage of total rainfall that is abstracted (lost) and does not contribute to runoff.
|
Time Of day
|
Cumulative rainfall (mm)
|
Instantaneous Runoff (m3/s)
|
|
4:00
|
0
|
0.0
|
|
4:30
|
30
|
0.3
|
|
5:00
|
80
|
4.2
|
|
5:30
|
90
|
11.3
|
|
6:00
|
95
|
13.0
|
|
6:30
|
127
|
34.0
|
|
7:00
|
130
|
45.3
|
|
7:30
|
132
|
21.2
|
|
8:00
|
|
9.3
|
|
8:30
|
|
4.8
|
|
9:00
|
|
2.5
|
|
9:30
|
|
1.4
|
|
10:00
|
|
0.8
|
|
10:30
|
|
0.0
|
|
Total
|
|
148.1
|
Q7) The parameters for Horton's equation are f0 = 3.0 in/h, fc = 0.5 in/h, and K = 4.0 h-1. Determine the infiltration rate and cumulative infiltration at 0.25-hr increments up to 4 hr from the beginning of infiltration. Assume continuous ponding.
Q8) Using the 1-hr unit hydrograph shown below, determine the direct runoff hydrograph for a 3-hr storm in which 1 in of excess rainfall occurred in the first hour, 2 in the second hour, and 0.5 in the third hour.
What is the area of the watershed in mi2?
|
Time period
|
Unit hydrograph (cfs)
|
|
0
|
0
|
|
1
|
100
|
|
2
|
300
|
|
3
|
500
|
|
4
|
700
|
|
5
|
400
|
|
6
|
200
|
|
7
|
100
|
|
8
|
0
|
Q9) A 600-hectare farm land receives annual rainfall of 2500 mm. There is a river flowing through the farm land with inflow rate of 5 m3/s and outflow of 4 m3/s. The annual water storage in the farm land system increases by 2.5 x 106 m3. Assuming there is no groundwater flow, then based on the system hydrologic budget equation, determine the annual evapotranspiration amount (in m3). [ Note: 1 hectare = 10,000 m2 ]
Q10) For the basin shown below, use (a) the Average method, b) The Thiessen method, and c) The Isohyetal method to estimate the average rainfall (in mm) on the basin.
