RN-23 : Irrigation return flow

Abstract

In irrigation practices, certain portion of the applied water, over and above the consumptive use, infiltrates into the ground to reach either an aquifer as deep percolation or to a nearby stream flow as inter flow. This contributory replenishment from irrigation is referred to as irrigation return flow. It includes the subsurface flow resulting due to excess percolation during irrigation together with the seepage from the conveying canal system. Excess percolation from the irrigated field itself accounts as much as 20% -40% of the volume of water applied for irrigation. The various factors affecting the irrigation return flow are namely the amounts of water diverted at the canal head for the purpose of irrigation, the hydrogeologic properties of the soils in the irrigated 'field, the conveyance and irrigation application efficiencies, the season of the year and the period of time through which the irrigation had been practised. Return flows from irrigation constitute a minor fraction in the hydrologic accounting of a watershed. However, the return flow is of great significance to the agriculturalist as well as to the economist. Return flows can be a valuable source of water supply for irrigation to water scarced areas. Additional project lands can be irrigated using the return flow . To the economist, return flow becomes an important element in planning the multipurpose use of water. In the present report, efforts have been made to study the return flow from irrigation and to understand the various factors affecting it. Efforts have been made to collect and review different methods of quantifying return flows from irrigation. Attention has been focussed on the analytical methods of return flow assessment and a few important case studies have been described.