Study of downward movement of soil water in unsaturated zones using isotopic techniques. Part of a coordinated programme on studying physical and isotopic behaviour of soil moisture in the zones of aeration

Experiments carried out to study the relative contribution from canal system, precipitation and irrigated fields to water table are described. The normal delta of irrigation water does not seem to have any appreciable effect on the water table through heavy textured soil. The contribution from irrigated fields and rains through sandy soils is significant. However, the groundwater rise (water logging) is mainly due to the infiltration from the canal system. Flow velocities at 1 m depth and 20 vol. % moisture are of the order of 16 m/a and 1.6 m/a for sandy and loamy soils respectively. The contribution from irrigated fields and rains to groundwater recharge is considered to be less than 30%