A watershed having an area of 4 km2 is subjected to a rainfall event of 9 cm, thereby generating stream flow at the outlet of the watershed for 10 h. If the average stream flow rate at the outlet of the catchment is 5 m3/s, occurring for a period of 10 h, the runoff co-efficient of the watershed for the storm is
1
0.3
2
0.5
3
0.6
4
0.4