(civl253)[2009](f)midterm~wmma^_10065.pdf

Back to CIVL253 Login to download

======================================================

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

Declaration on Academic Integrity

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