# Flood Routing and Flood Control

 Question 1
A flood control structure having an expected life of n years is designed by considering a flood of return period $T$ years. When $T=n$, and $n\rightarrow \infty$, the structure's hydrologic risk of failure in percentage is . (round off to one decimal place)
 A 25.2 B 68.4 C 78.2 D 63.5
GATE CE 2022 SET-2   Engineering Hydrology
Question 1 Explanation:
Risk of failure $=1-q^n=1-(1-p)^n=1-\left ( 1-\frac{1}{T} \right )^n$
For $T=n\rightarrow \infty$
Risk of failure $=1-\frac{1}{e}=0.632$
% risk of failure = 0.632 x 100=63.2%
 Question 2
Superpassage is a canal cross-drainage structure in which
 A natural stream water flows with free surface below a canal B natural stream water flows under pressure below a canal C canal water flows with free surface below a natural stream D canal water flows under pressure below a natural stream
GATE CE 2020 SET-2   Engineering Hydrology
Question 2 Explanation:
Cross-section of a super passage Question 3
Muskingum method is used in
 A hydrologic reservoir routing B hydrologic channel routing C hydraulic channel routing D hydraulic reservoir routing
GATE CE 2020 SET-2   Engineering Hydrology
Question 3 Explanation:
Muskingum method is used in hydrological channel routing
 Question 4
In a homogeneous unconfined aquifer of area 3.00 $km^2$, the water table was at an elevation of 102.00 m. After a natural recharge of volume 0.90 million cubic meter ($Mm^2$), the water table rose to 103.20 m. After this recharge, ground water pumping took place and the water table dropped down to 101.020 m. The volume of ground water pumped after the natural recharge, expressed (in $Mm^2$ and round off to two decimal places), is ______.
 A 0.5 B 1 C 1.5 D 2.5
GATE CE 2020 SET-1   Engineering Hydrology
Question 4 Explanation: \begin{aligned} V_R&=0.9Mm^3\\ V&=3 \times (103.2-102)\\ y_s \; \text{or}\; y_R&=\frac{VR}{V}=\frac{0.9}{3.6}\\ \text{Now,}\;\; y_s&=\frac{V_D}{V}\\ V_D&=\frac{0.9}{3.6}[3 \times (103.2-101.2)]\\ V_D&=1.5Mm^3 \end{aligned}
 Question 5
The probability that the annual maximum flood discharge will exceed 25000 $m^3/s$, at least once in next 5 years is found to be 0.25. The return period of this flood event (in years, round off to 1 decimal place) is ____
 A 12.2 B 16.4 C 17.9 D 20.6
GATE CE 2019 SET-1   Engineering Hydrology
Question 5 Explanation:
\begin{aligned} \text{Risk} &=1-q^n \\ 0.25&=1-q^5 \\ q&=0.944087 \\ 1-p&=0.944087 \\ 1-\frac{1}{T}&=0.944087 \\ T&\simeq 17.9 \; \text{years} \end{aligned}

There are 5 questions to complete.