Infiltration Indices

Q. The rate of rainfall for successive $30minutes$ period of a $4-hour$ storm are as follows:
$3.5,6.5,8.5,7.5,6.4,4.0,4.0,6.0cm/hr.$ If the value of $\varphi -index$ is $4.5cm/hr$, then the value of W- index (cm/hr) is

1. 5.5
2. 4.13
3. 4.25
4. 3.9

Q. A 6-hour rainstorm with hourly intensities of 7, 18, 25, 12, 10 and 3 mm per hour produced a run-off of 33 mm. Then the $\varphi -$ index is

1. 7 mm/h
2. 3 mm/h
3. 10 mm/h
4. 8 mm/h

Q. The rainfall on five successive days in a catchment was measured as 3, 8, 12, 6 and 2 cm. If the total runoff at the outlet from the catchment was 15 cm, the value of the $\varphi -index$ (in mm/hour) is

1. 0.0
2. 1.04
3. 1.53
4. Sufficient information not available

Q. The intensity of the rainfall for successive 1 hr period of a 6 hr storm are 2, 6, 8, 9, 7 and 3 cm/hr. The runoff is 4 cm/hr. Calculate the $\varphi -index$ (in cm/hr).

1. 2.5
2. 3.5
3. 4.6
4. 7.67

Q. The total observed runoff volume during a 4 hour storm with a uniform intensity of 2.8 cm/hr is $25.2\times {10}^6{m}^3$ from a basin of $280k{m}^2$ area. What is the average infiltration rate for the basin?

1. 3.6 mm/hr
2. 4.8 mm/hr
3. 5.2 mm/hr
4. 5.5 mm/hr

Q. The rainfall during three successive 2 h periods are 0.5, 2.8 and 1.6 cm. The surface runoff resulting from this storm is 3.2 cm. The $\varphi$ index value of this storm is

1. 0.20 cm/h
2. 0.28 cm/h
3. 0.30 cm/h
4. 0.80 cm/h

Q. A storm with 14 cm precipitation produced a direct runoff of 8 cm. The time distribution of the storm is as shown in the table below:

$\begin{array}{cc}\text{Time from}& \text{Incremental}\\ \text{start(h)}& \text{Rainfall in cm}\\ 1& 1.0\\ 2& 2.0\\ 3& 2.8\\ 4& 3.3\\ 5& 2.5\\ 6& 1.8\\ 7& 0.6\end{array}$

What is the value of $\varphi -index$ of the storm?

1. 0.5 cm/h
2. 0.7 cm/h
3. 0.8 cm/h
4. 0.9 cm/h

Q. A 4 hr storm had 4 cm of rainfall and the resulting direct runoff was 2.0 cm. If the $\varphi -index$ remains at the same value, the runoff due to 10 cm of rainfall in 8 hr in the catchment is

1. 6.0 cm
2. 7.5 cm
3. 2.3 cm
4. 2.8 cm

Q. A 6-hours rainstorm with hourly intensities of 7, 18, 25, 17, 11 and 3 mm/hour produced a runoff of 39 mm. Then the $\varphi -index$ is

1. 3 mm/hour
2. 7 mm/hour
3. 8 mm/hour
4. 10 mm/hour

Q. A 3-hour storm on a small drainage basin produced rainfall intensities of 3.5 cm/hr, 4.2 cm/hr and 2.9 cm/hr in successive hours. If the surface runoff due to the storm is 3 cm, then the value of $\varphi -index$ will be

1. 2.212 cm/hr
2. 2.331 cm/hr
3. 2.412 cm/hr
4. 2.533 cm/hr

Q. The hyetograph of a storm event of duration 140 minutes is shown in the figure.



The infiltration capacity at the start of this event (t = 0) is 17 mm/hour, which linearly decreases to 10 mm/hour after 40 minutes duration. As the event progresses, the infiltration rate further drops down linearly to attain a value of 4 mm/hour at t = 100 minutes and remains constant thereafter till the end of the storm event. The value of the infiltration index, $\varphi$(in mm/hour, round off to 2 decimal places), is

1. 5
2. 7.25
3. 8.5
4. 12

Q. Direct runoff from a flood over a basin of area 50 hectare was observed as $25000m^3$ during a storm. The equivalent depth of rainfall over the basin was 97 mm. The time distribution of the rainfall during the storm is given below. Determine the $\varphi -index$ for the storm.
$\begin{array}{ccccccccc}\text{Time(hr.)}& 0& 1& 2& 3& 4& 5& 6& 7\\ \text{Rainfall(mm)}& 0.0& 6.0& 11.0& 34.0& 28.0& 12.0& 6.0& 0.0\end{array}$

1. 8.75

Q. During a storm event in a certain period, the rainfall intensity is 3.5 cm/hour and the $\varphi -index$ is 1.5 cm/hour. The intensity of effective rainfall (in cm/ hour up to one decimal place) for this period is

1. 2

Q.

The average rainfall in a town is $19.6cm$ in $4$ weeks. How much rain falls on an average , in $17$ days $?$