Modeling the Effect of Floodwater Spreading Systems on the Soil–Water Balance and Crop Production in the Gareh Bygone Plain of Southern Iran

Abstract

Between 1983 and 1987, eight floodwater systems were constructed covering 1,365 ha in the Gareh Bygone Plain of southern Iran. The floodwater sys tems have areas between 25 and 365 ha and on average 10 million m³ of floodwater is diverted annually to the systems. A soil–water balance model was used to evaluate the recharge of the groundwater and the increased crop transpiration on the terraces of the floodwater systems. A simulation showed that, as a result of the construction of the system, the recharge increases on average on the terraces by four-fold. In a dry year, 27% of the infiltrated rain and floodwater percolates on average to the aquifer and the recharge increases up to 69% in a humid year. Indigenous vegeta tion of bushes and shrubs grow well on the terraces. Commercially more attractive trees, such as the eucalyptus, are, because of their high water consumption, only very productive in years where runoff/run-on events are important both in magnitude and number. Nevertheless, thanks to their vigorous growth, eucalyptus trees produce on average more above-ground biomass than the indigenous vegetation. It is estimated that thanks to the additional water supplied by run-on, the cultivation of barley on the terraces during the rainy season can triple their production in the region.