Question

(c) Using the Rational Method as described in AR & R for Victorian conditions and information supplied, determine the design flood in the Campaspe River catchment for an ARI of 50 years at the Rochester Gauging Station using a standard equation for determination of time of concentration for Victoria. Adopt Cy 0.18 and Area of catchment 1312 square miles.Use the Rainfall Intensity Frequency Duration Curves for Melbourne which is attached in Appendix (d)Records show that the instantaneous maximum flow at the Rochester Gauging Station was 1699 cumecs, measured on the 23 September 1916. What is your impression about this flow on comparing with the calculated, values above?

Answer 1

Ans c) We know, according to rational method,

Q = C i A ,

where, C = coefficient of runoff

i = rainfall intensity (in/hr)

A = area of catchment in acres

According to IDF curve of Melbourne for 50 year ARI , i = 3.93 in/hr

Area = 1312 sq miles or 839680 acre

=> Q = 0.18 x 3.93 x 839680

= 593990 ft³/s

or 16820 m³/s

Ans d) As the calculated discharge = 16820 cumecs and records shown at station was 1699 cumecs, therefore we can see that the recorded values are correct.