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(civl253)[2009](f)midterm~wmma^_10065.pdf
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CIVL253 CHYDROLOGY Mid-term Examination (27 October 2009)
Name (English/Chinese)
Student Number:
Problem 1 / 25
Problem 2 / 30 Problem 3 / 25 Problem 4 / 30
Total Score / 100
declare that the answers submitted for this examination are my own work.
I understand that sanctions will be imposed, if I am found to have violated the University regulations governing academic integrity.
Student's Signature:
Note:
(1)
This is a close-book examination. No reference material of any kind can be used during the examination.

(2)
All computation steps must be shown and described clearly - without them, no score will be given.

(3)
Assumptions made must be clearly stated and justified.

(4)
Proper units must be attached.

Problem 1 (25%)
A river flowing by a village situated in a low lying area has 4 years of discharge measurements. The peak discharges in the river exceeding 200 m3/s over the record period are shown in the table below. Due to frequent flooding of the village, a dike system is to be constructed by a local government for protecting the village. From the viewpoint of safety and cost, local government decided that the dike system should be designed to have a failure probability of 0.20 over an expected service period of 10 years.
(a)
What should be the value of design return period for the dike system? (5%)

(b)
Based on annual maximum floods, determine the magnitude of design discharge corresponding to the return period obtained in part (a) by the L-moment method under a generalized Pareto distribution and plotting position formula of (i-0.35)/n. (8%)

(c)
Due to relatively short stream flow record, the underlying distribution is uncertain. To have some idea about the effect of using different distributions, you are asked to re-calculate design discharge for the dike system based on annual exceedance floods using the frequency factor method under a blog-normal distribution. (7%)

(d)
Based on the two values of design flood, which value would you recommend for the design. Please explain your rationales. (5%)

Year Discharge, m3/s
1971 334, 424
1972 405, 215, 306
1973 328, 247, 307
1974 291, 397

Problem 2 (35%)
Consider a watershed with drainage area of 1 km2. For a given storm event, the recorded average rainfall intensity and total instantaneous discharge at the outlet of the watershed are listed in the following table. Assume that the baseflow is 2 m3/s and rainfall amount in the first 30 minutes is the initial loss.
(a)
Determine the total amount of rainfall? (5%)

(b)
Determine the volume of direct runoff? (10%)

(c)
Determine the average infiltration rate, i.e., index (10%)

(d)
Determine the rainfall excess intensity hyetograph corresponding to the index obtained in (c). Also, what is the duration of rainfall excess hyetograph. (5%)

Time (min) Intensity (mm/h) Discharg