3. The ryots always, and justly, prefer running toMoving water best for crops as for health. stagnant water. Irrigation with stagnant water is injurious to health and also to vegetation. Irrigation should be accompanied by improving the natural drainages of the country, so as to keep the water moving, however slowly.
But the difficulty is said to be, how to supply moving water, and make the works pay at the same time, for the whole surface of the country. Everywhere, however, water can be supplied for irrigation at a cost enormously below its value—the average cost of water in works on a large scale being about £2 per acre of rice.
Irrigation works are planned generally to supply one cubic foot per second to every 133 acres, which is the same as one cubic yard per acre per hour, or ⅕ inch in depth on the surface per day. Two-thirds of a cubic yard per hour for 100 days are given for wheat or other 'dry grain,' and two cubic yards per hour for 120 days for rice, including rain—i.e. ⅛ inch per day for dry grains and ⅜ for rice.
To this extent, even if every cultivable acre in the country were irrigated, we can change the water; but, as only a certain proportion of the area commanded by the canals is irrigated, and of this all is not receiving water at the same time, we do, in fact, supply a greater depth, and in that degree renew the water lying on the surface.
In the rice districts in Madras the whole area is irrigated: in the wheat country out of the tropics in