Extracted text: If the mean annual runoff of a drainage basin of 10000 km? is 140 m/sec, and the average annual precipitation is 105 cm, Estimate the annual average ET for this basin. The mass curve of rainfall as one of the hydrological key concepts in a storm of total duration 120 minutes as shown in table below. Estimate the amount of rainfall in this storm if the area of the watershed is 4000000 cm?. Table Time 20 40 60 80 100 120 (minute) Cumulative Rainfall (cm) 0.2 0.8 1.6 2.0 2.2 2.5