The watershed at a site on a stream has 77000 ha area. The mean annual precipitation at this place is 950 mm. (i) if 25% of rainfall reaches the basin outlet as stream flow , estimate the mean annual?

stream flow at the outlet of the basin.

Given:
Watershed area = 77000 ha = 77000 * 10000 m^2 = 770000000 m^2
Mean annual precipitation = 950 mm = 0.95 m
Percentage of rainfall reaching the basin outlet as stream flow = 25%

Total annual precipitation reaching the basin = Watershed area * Mean annual precipitation
Total annual precipitation reaching the basin = 770000000 m^2 * 0.95 m = 731500000 m^3

Mean annual stream flow at the outlet of the basin = Percentage of rainfall reaching the basin outlet as stream flow * Total annual precipitation reaching the basin
Mean annual stream flow = 0.25 * 731500000 m^3 = 182875000 m^3

Therefore, the mean annual stream flow at the outlet of the basin is 182,875,000 cubic meters.