Probability of Rainfall Event

Q. The return period for the annual maximum flood of a given magnitude is 8 years. The probability that this flood magnitude will be exceeded once during the next 5 years is

1. 0.625
2. 0.366
3. 0.487
4. 0.529

Q. The probability that a 100 years flood is equalled or exceeded, at least once in 100 years is

1. 99%
2. 64%
3. 36%
4. 1 %

Q. Probability of a 10 year flood to occur atleast once in the next 4 years is

1. 25%
2. 35%
3. 50%
4. 65%

Q. The analysis of maximum daily rainfall on a city indicated that a depth of 300 mm has a return period of 60 years. The probability of one day rainfall depth equal to or greater than 300 mm in the city occurring exactly two times in 15 successive years is

1. 1.981%
2. 2.344%
3. 4.325%
4. 3.788%

Q. A bridge has an expected life of 50 years and is designed for a flood magnitude of return period 100 years. The risk associated with this hydrologic design is _______ %. Also, the return period in design which would have reduced the risk to 25% will be _____ years.

1. 55.2% 28 years
2. 39.8%, 94 years
3. 39.5%, 16 years
4. 55.9%, 46 years

Q. Recorded annual maximum 24-hour rainfall magnitudes at stations 'X' are as under:

$\begin{array}{cc}\text{Years}& \text{Rainfall (cm)}\\ 1960& 12.0\\ 1961& 6.0\\ 1962& 4.8\\ 1963& 7.9\\ 1964& 12.0\\ 1965& 14.2\\ 1966& 13.6\\ 1967& 6.0\\ 1968& 3.7\\ 1969& 2.9\end{array}$

What is the return period, in years, for a 6.0 cm annual rainfall according to (i) Hazen formula and (ii) Weibull formula; respectively?

1. $\frac{10}{7},\frac{11}{7}$
2. $\frac{20}{13},\frac{22}{13}$
3. $\frac{5}{3},\frac{11}{7}$
4. $\frac{20}{11},\frac{11}{6}$

Q. A 1-h rainfall of 10 cm magnitude at a station has a return period of 50 years. The probability that a 1-h rainfall of magnitude 10 cm or more will occur in each of two successive years is:

1. 0.04
2. 0.2
3. 0.02
4. 0.0004

Q. From the analysis of rainfall data at a particular station, it was found that a rainfall of 400 mm had a return period of 20 years. What is the probability of rainfall equal to or greater than 400 mm occurring atleast once in 10 successive years?

1. $(0.95{)}^{10}$
2. $1-(0.95{)}^{10}$
3. $1-(0.05{)}^{10}$
4. $(0.05{)}^{10}$

Q. A culvert is designed for a flood magnitude of return period 100 years and has expected life of 20 years. The risk in this hydrologic design is

1. $1-{0.99}^{20}$
2. $1-{0.01}^{20}$
3. $1-{0.09}^{20}$
4. $1-{0.10}^{20}$

Q. A hydraulic structure has an expected life of 20 years and is designed for a flood magnitude of return period 50 years. The risk of failure of the structure during its life is

1. 0.87
2. 0.33
3. 0.60
4. 0.13

Q. A temporary coffer dam is to be built to protect the 5 year construction activity for a major cross valley dam. If the coffer dam is designed to withstand the 20 year flood, the risk that the structure will be over topped in the third year exactly is ______ (in percentage)

1. 4.51

Q. The hydrologic risk of a 100-year flood occurring during the 2-year service life of a project is

1. 9.8%
2. 9.9%
3. 19.9%
4. 1.99%

Q. The probability of a 10 years flood to occur at least once in the next 5 years is

1. 35%
2. 41%
3. 60%
4. 65%

Q. A bridge has an expected life of 50 years and is designed for a flood magnitude of return period 100 years. What is the risk associated with this hydrologic design?

1. $1-(0.99{)}^{50}$
2. $(0.5{)}^{50}$
3. $(0.99{)}^{50}$
4. $(0.99{)}^{100}$

Q. The probability that the annual maximum flood discharge will exceed $25000{\text{m}}^3/\text{s}$, at least once in the 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

1. 17.9

Q. What is the probability of a 20 year flood occurring four times in the next 20 years ?

1. 0.0133
2. 0.133
3. 0.00133
4. 0.000133

Q. It is proposed to design a causeway along a village road. The return period for the annual maximum flood of a given magnitude was found to be 5 years. The probability that this flood magnitude will be exceeded atleast once during next 2 years is:

1. 0.8
2. 0.5
3. 0.45
4. 0.36

Q. Return Period Refers to

1. The Probability of Exceedance of an event
2. The Probability of Non-Exceedance of an event
3. The Inverse of the Probability of Exceedance of an event
4. The Inverse of the Probability of Non­ Exceedance of an event

Q. For a station Q, the recorded annual maximum 24-hour rainfall magnitudes are given in the table:
$\begin{array}{cccccccc}\text{Year}& 1999& 2000& 2001& 2002& 2003& 2004& 2005\\ \text{Rainfall (cm)}& 13& 12.7& 15& 14.1& 11& 13.8& 11.3\end{array}$

Using Hazen's formula, the rainfall with a return period of 2 years is ______ cm.

1. 13

Q. The probability that a 100 year flood is equalled or exceeded, at least once in 100 years is

1. 99%
2. 64%
3. 36%
4. 1%

Q. Which of the following statement(s) is/are INCORRECT ?

1. Maximum intensity for a given return period decreases as the duration increases.

2. Maximum intensity of given duration increases as the return period increases

1. 1 only
2. 2 only
3. 1 and 2 both
4. None

Q. The probability of a 10 year flood to occur atleast once in the next 4 years is

1. 45%
2. 35%
3. 30%
4. 20%