An agricultural watershed was urbanised over a period of 30 years. The rainfall loss was 9 mm/hr before urbanisation, which dropped to 4 mm/hr after urbanisation. The 1-hr UG (unit 1 cm) of this watershed can be assumed as a triangle of base 12 hr and height 160 cumec after 4 hr before urbanisation and of base 8 hr and height 240 cumec after 3 hr, after urbanisation.
(a) Determine the area of the watershed.
(b) Draw the flood hydrograph after urbanisation for a storm of intensity 19 mm/hr for 1 hr and 29 mm/hr in the next door. Assume a uniform loss rate and a constant base flow of 10 cumec.
(c) Compute the coefficient of runoff before and after urbanisation.