Let us consider in a given area the plantation of a certain crop takes 20 days, and the total water depth required by this crop is 80 cm on the field. Find the duty of irrigation water required for the crop during this period.
(a) Assuming 20% losses of water in the water courses, find duty at the head of the course.
(b) Find the duty of the water at the head of the distributary, assuming 10% losses from the distributary head.