GATE Papers >> Civil >> 2019 >> Question No 160

Question No. 160

The ordinates, u, of a 2-hour unit hydrograph (i.e., for 1 cm of effective rain), for a catchment are shown in the table.

 t (hour) 0 1 2 3 4 5 6 7 8 9 10 11 12 u (m3/s) 0 2 8 18 32 45 30 19 12 7 3 1 0

A 6-hour storm occurs over the catchment such that the effective rainfall intensity is 1 cm/hour for the first two hours, zero for the next two hours, and 0.5 cm/hour for the last two hours. If the base flow is constant at 5 m3 /s, the peak flow due to this storm (in m3 /s, round off to 1 decimal place) will be _______

Solution of Question No 160 of GATE 2019 Civil Paper

For the first two hours  ⇒ rainfall intensity = 1 cm/hr ⇒ rainfall = 2cm

2-4 hours                ⇒ 0

 Time 2-hr UH 2hr $\times$ Prceci 2hr UH lagged by 2 hr Lagged by 4 hr R = 2 $\times$ 0.5 = 1cm Total DRH 0 0 0 - - 0 1 2 4 - - 4 2 8 18 0 - 16 3 18 36 0 - 36 4 32 64 0 0 64 5 45 90 0 2 92 = Peak 6 30 60 0 8 68 7 19 38 0 32 70 8 12 24 0 45 69 9 7 14 0 30 44 10 3 6 0 19 25 11 1 2 0 12 14 12 0 0 0 7 3

Peak of flood=92+base flow=92+5=97