CSIR NET June 2016 Q42: Hydrology
The recurrence interval (or return period) T of a flood of a given magnitude is the reciprocal of its annual exceedance probability P, i.e. T = 1/P. This gives the average number of years between floods that equal or exceed that level, though it does not mean such floods occur at exactly regular intervals.
Given that the annual probability of the water level equaling or exceeding the marked high-flood level is P = 0.01:
Recurrence interval T = 1 / P = 1 / 0.01 = 100 years
So floods that equal or exceed this level are expected to recur, on average, once every 100 years.
Recurrence interval T = 1 / P = 1 / 0.01 = 100 years
So floods that equal or exceed this level are expected to recur, on average, once every 100 years.
Option 1 (1 year) would correspond to a probability of 1.0 (certainty every year), not 0.01.
Option 2 (10 years) would correspond to a probability of 0.1, ten times higher than the given value.
Option 3 (100 years) is correct, directly following from T = 1/0.01 = 100.
Option 4 (1000 years) would correspond to a probability of 0.001, ten times lower than the given value.
Option 2 (10 years) would correspond to a probability of 0.1, ten times higher than the given value.
Option 3 (100 years) is correct, directly following from T = 1/0.01 = 100.
Option 4 (1000 years) would correspond to a probability of 0.001, ten times lower than the given value.