Urbanizing Irrigated Valleys for Optimum Water Use

Urbanization of irrigated valleys presently tends to be concentrated on the irrigated land. This not only causes permanent loss of agricultural land, it also makes it difficult to renovate and reuse the sewage effluent and to effectively utilize rainfall runoff. Better water reuse is possible if the urbanization were to take place on the unirrigated lands surrounding the valley. Sewage effluent could then be renovated by ground-water recharge via rapid-infiltration systems on the valley periphery. The renovated water would move underground to the irrigated parts of the valley, where it could be pumped from wells for unrestricted irrigation. Available water would thus be used twice: first by the municipalities and then by irrigation. Storm runoff from the urban developments could be spread over agricultural fields for irrigation or ground-water recharge. Ground-water could be managed to avoid water-table declines, while removal of the upper ground-water (via drains or shallow wells) below the irrigated fields would make it possible to maintain a salt balance for the entire valley.