Time of concentration

The R.L. of ground water table on the sides of a valley is 1505 m whereas R.L. of the stream water is 1475 m. If 60° slope consists of pervious soil between R.L. 1485 m to 1500 m, the gravity spring may be expected at the point of reduced level

While determining the yield of open wells by the pumping test

If four fires break out in a city of population 40 lakhs and if each hydrant has three streams and duration of each fire is four hours, the total quantity of water required, is