Question

1. Write at least two sentences in your own words to explain the difference between the recurrence probability of a given flow magnitude and the risk probability of observing an event equal or greater than that magnitude.

2. Answer True or False and justify your answer:

    a. The risk probability can be obtained from historical data by looking the number of events with equal or higher magnitude and divide it by the total number of years with data collections.

    b. Probability of no 100 yr event occurs in n = 25 yr is P = 0.778 = 77.8 %. Therefore, probability of at least one event in these 25 yrs is observed = 22.2 %

Answer 1

1) RECURRENCE PROBABILITY OF A GIVEN FLOW INDICATES INVERSE OF RETURN PERIOD I.E. IF RECURRENCE PROBABILITY = 0.04 INDICATES FREQUENCY OF FLOW TO BE 25 YEARS. WHILE RISK PROBABILITY SHOWS FOR A PARTICULAR PERIOD IN WHICH EVENT WILL BE EQUAL OR GREATER THAN THAT MAGNITUDE HAPPENS ATLEAST ONCE I.E. IF RISK PROBABILITY =0.04 FOR 25 YEARS THEN THIS MEANS THAT EVENT WILL OCCUR ATLEAST ONCE IN 25 YEARS. 'ATLEAST' IS THE KEYWORD FOR MAJOR DIFFERENCE.

2) (a) FALSE .. THIS PROCEDURE IS FOR RECURRENCE PROBABILTY.

(b) TRUE... BECUAUSE P(AT LEAST ONCE) =P(1) +P(2) +P(3) + - - - - - - - = 1- P(0)

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