The Role of Agricultural Management in Sustaining Zayandeh-rud Flow

Management of agricultural practices plays a vital role in reducing the use of limited water resources in arid and semi-arid regions which could result in their sustainability. In this research, the role of managing agriculture in sustaining flow of Zayandeh-rud was studied by calculation of rice water requirement (actual evapotranspiration) in paddy fields of Zarrin-shahr by using method of FAO-56 and comparing the results assuming a shift in cropping pattern from rice to other crops. Rice water requirement was estimated at 1485 mm and the volume of water required for irrigation of paddy fields with area of about 6630 Hectare was estimated at 77 MCM. Volume of irrigated waterwas also evaluated by water balance method, confirmed the reliability of FAO-56 method. The results show that, replacing rice or wheat-rice cropping pattern with some possible crops such as bean, maize, walnut, apple and grape decreases irrigation requirements about 27, 15, 24, 29 and 40 MCM, respectively. Generalizing results for the total paddy fields in Isfahan Province with estimated area of about 20000 Hectare will result in an increase of about 3.4 to 9.1 m3/s in Zayandeh-rud discharge during critical months of June to October, when the river flow highly decreases, causing sustainable flow of the river through the year.