Estimation of monthly abstracted groundwater rate in Zayandehrud irrigation main network

Almost two-third of demand water of Zayandehrud basin, which is equal to 3500 million cubic meters, is supplied by groundwater, especially by wells. This water is used mainly for irrigation.Because of recent droughts and consequent decreased discharge of Zayandehrud, demand for groundwater has increased, leading to a sharp decline of groundwater levels in most of plains of the basin. Statistical analysis of meteorological data and pizometric wells shows a downward trend of drawdown of water table continues. This situation has created difficulties for developments of province Isfahan. So, it is urged to both decrease groundwater abstraction, and increase water productivity. To reach this objective, it would be useful to estimate the monthly abstracted groundwater in the irrigation networks. In this research, the necessary maps were prepared by using data collected from wells, questionnaires addressing the farmers, and Ilwis software. These maps once were superimposed, served to convert the annual abstracted well discharge in plaines to monthly abstracted discharge in the main irrigation networks. Finally, the gross rate of annual and monthly consumed water per hectare was obtained for irrigation networks of right bank of Nekoabad, left bank of Nekoabad, right bank of Abshar, left bank ofAbshar, Mahyar-Jarghooyeh, Borkhar and of average of total networks. The rate of annualconsumed water per hectare during agricultural year (Oct. 2003 to Oct. 2004) estimated for the mentioned networks were: 15011, 7014, 11509, 4952, 1444, 2662 and 5302 m3, respectively. These values may vary following climatic conditions, crop pattern and other parameters. Meanwhile their initial estimations and their comparison can help to improve water productivity in this basin.