Question 4 (5 marks) a) ? Using the Intensity-Frequency-Duration information sho

Question

Question 4 (5 marks) a) ? Using the Intensity-Frequency-Duration information shown in Figure Q4, Average Recurrence Interval (ARI) for: i) a storm lasting 2 hours in which the total rainfall is 65 mm (1 mark) i) a storm lasting 4 hours in which the total rainfall is 120 mm; (1 mark) (1 mark) b) Briefly explain why no lines are shown in Figure Q4 for Average Recurrence Intervals of ii) a storm lasting 1 hour in which the total rainfall is 80 mm. 200 years and 500 years. (2 marks) FD Table Coefficients ARI Print IFD chart Help IFD chart 600 500 600 500 400 DESIGN RAINFALL INTENSITY CHART

Explanation / Answer

(a) From the given IDF Curves,

(i) For Duration = 2 hrs (X-axis) and total rainfall of 65mm (which is equal to intensity of 65mm/2hrs = 32.5mm/hr on Y-axis), the ARI (also called as Return Period) is 2 Years.

(ii) For Duration = 4 hrs (X-axis) and total rainfall of 120mm (which is equal to intensity of 120mm/4hrs = 30mm/hr on Y-axis), the ARI (also called as Return Period) is 10 Years.

(iii) For Duration = 1 hrs (X-axis) and total rainfall of 80mm (which is equal to intensity of 80mm/1hr = 80mm/hr on Y-axis), the ARI (also called as Return Period) is 10 Years.

(b) For ARI equal to and less the length of the available rainfall record, the IDF curves generated from the yearly maximum rainfalls gives optimum results. Whereas, for ARI more than the length of the available rainfall record, the extrapolation of intensity values for higher return periods will have high error (or deviation), hence will not yield optimum results.

Related Questions

Navigate

• Browse (All)
• Browse Q
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.