Environmental Engineering Questions and Answers – Rational Method

This set of Environmental Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Rational Method”

1. The runoff in cumec by the Rational method is defined by ______________
a) Q = K*A*I*R
b) Q = (K+A+I) *R
c) Q = (K+A) *R
d) Q = A*I*R

Explanation: According to the Rational method, the storm water or runoff is defined by Q = K*A*I*R where, ‘K’ is a constant, ‘A’ is the catchment area in hectares,’I’ is the impermeability factor and ‘R’ is the intensity of rainfall in mm per hour.

2. The value of the factor K in finding the storm water flow by Rational method is ____________
a) 100
b) 160
c) 1
d) 1/360

Explanation: According to the Rational method, the storm water or runoff is defined by
Q = K*A*I*R where, K is a constant and K = 1/360,
So, Q = A*I*R/360.

3. _______ is defined as the percentage of rain water in the form of runoff.
a) Storm water flow
b) Coefficient of permeability
c) Impermeability factor
d) Coefficient of consolidation

Explanation: Impermeability factor is defined as the percentage of rain water in the form of runoff. The storm water flow depends on the imperviousness of the surface and if it is more, more runoff takes place.

4. The impermeability factor is also called as ____________
a) Coefficient of impermeability
b) Runoff coefficient
c) Coefficient of permeability
d) Precipitation factor

Explanation: The impermeability factor is also called as runoff coefficient and it includes Kuichling’s impermeability factor and Fruhlings factor.

5. Which of the following surface has a maximum Kuichling’s impermeability factor?
b) Water tight roof surface
c) Unpaved surface

Explanation: The water tight roof surface has maximum Kuichling’s impermeability factor with a magnitude of 0.7 to 0.95 while gravel road, unpaved surface and macadamized road ways have < 0.7.
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6. Which of the following locality has a minimum Fruhlings factor?
b) An area closely built up
c) Area with 50% attached and detached houses
d) Extremely suburban area

Explanation: Extremely suburban area having 20% to 60/5 parking and widely detached houses has a minimum Fruhlings factor with a magnitude of 0.35 while business area, closely built up area and area with 50% attached and detached house have magnitude > 0.35.

7. If the type of surface is of the most densely populated portion of the city, what is the value of Kuichling’s impermeability factor?
a) 0.14
b) 0.30
c) 0.80
d) 0.45

Explanation: The value of Kuichling’s impermeability factor for a surface of the most densely populated portion of the city lies between 0.7 to 0.9.

8. The value of Fruhlings factor for suburban locality is ______
a) 0.10
b) 0.20
c) 0.50
d) 0.80

Explanation: If the type of locality is suburban area having detached houses, the value of Fruhlings factor lies in the range of 0.45 to 0.55.

9. The storm frequency for a peripheral residential area is ___ a year.
a) Once
b) Twice
c) Thrice
d) 4 times

Explanation: The frequency of storm for which the sewer is to be designed for a peripheral residential area is twice a year.

10. The storm frequency for a peripheral commercial area is ____________
a) Once a year
b) Twice a year
c) Once in 2 years
d) Once in a month

Explanation: The commercial and higher priced area more subject to less storm frequency than the residential area and its storm frequency is once in 2 years.

11. Shorter the duration of rainfall ____ will be the rainfall intensity.
a) Lesser
b) Constant
c) Slightly lesser
d) Greater

Explanation: The intensity of rainfall is inversely proportional to the duration period, so the shorter the duration of rainfall, greater will be the rainfall intensity.

12. When the storm occurs once a year, the rainfall intensity R is ____________
a) R = 300/t0.625
b) R = 150/t0.625
c) R = 150/t2
d) R = 300/t2

Explanation: When the storm occurs once a year, the rainfall intensity R is given by R = 150/ t 0.625 Where, t is the duration of storm in minutes.

13. The Kuichlings formula when the storm occurs once in 10 years is ____________
a) R = 2667/(t + 50)
b) R = 260/(t + 20)
c) R = 2667/(t + 20)
d) R = 260/t

Explanation: According to Kuichling, when the storm occurs once in 10 years, the rainfall intensity R is given by R = 260/(t + 20) and when it occurs once in 15 years, it is given by R = 3048/(t + 20) where t is the duration of storm in minutes.

14. ________ is the time required by flood discharge to reach the maximum limit.
a) Storm frequency
b) Run-off time
c) Detention period
d) Time of concentration

Explanation: The time of concentration is defined as the longest time required for a drop of water to flow from the farthest point of drainage area to the point of concentration.

15. The maximum runoff occurs when the duration of storm equals the time of concentration.
a) True
b) False

Explanation: It is because if duration of storm is shorter than time of concentration, then whole catchment will not be the contributing water, resulting in lesser runoff whereas if duration of storm exceeds the time of concentration, then rainfall intensity will be less, resulting in lesser runoff.

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