Question

6. a) The hydrograph observed at the outlet of a basin of area 160 km2 is given in a table below. It is assumed that the rainfall intensity is constant at 50 mm/hr and the infiltration index is 10 mm/hr. Derive the unit hydrograph of a basin. t(min) 30 60 90 120 150 Q (m/s) 200 800 1400 800 200 200 0 b) Please calculate the total runoff hydrograph (with baseflow) if uniform rainfall depth 2cm occurs within an hour.

Answer 1

Given Hydrography O 30 Time & (m3/40) 200 800 GO 1400 go 1800 120 200 150 200 Area of basin = 160 km² = 160x100 m² (P) Rainfall intensity = Somm/he = scmlhs. Infiltration index ($) = lomrolha = I emolha. wen know that IR=p-ot R = Run off ( effectue rainfall) (cm) P = Rainfall (cm) $ - Infiltation Index (cm/hs), R = ļo 7 E R = 5-1= 4 cm/h ( for one hour). for 30 min. time duration R= ucm 8cm o she

Unit hydrograph flood hydrograph Runoff depth time I &(m/sec) o 200/8 - 25 30 | 800/8 = 100 60 1400/8 = 175 go 1 80018 = 100 120 200/8 = 25 150 200/8 = 251 2 P= 2 cmhe. &= 1 colhe. R= p-o. € R=10m/h E Z Total runoff hydrograph time. 8(molarec) O 25/1=85 30 100/1 =100 GO 175/1 = 145 go 100/1 = 100 120 9511 150 2511 25' = 25