Simulation of salinity expansion upstream of Qazvin saltmarsh interception drain in conditions of ground water overexploitation

A large part of Iran suffer from salinity which threatens sustainable agriculture and food security. Overexploitation of groundwater, where fresh and saline aquifers are adjacent to each other increasing saline water hydraulic gradient and solute transport toward fresh aquifer and increasing salinity. In Qazvin saltmarsh salinity is expanding toward upstream lands under the mentioned mechanism. An interception drain has been constructed in area in order to drive out saline water and control salinity. The purpose of this study is to assess interception drain ability in controlling salinity and the effect of hydraulic gradient increase and decrease on salinity expansion toward upstream lands. Thus first using observed data the HYDRUS-2D model was calibrated and validated. Then in six treatments, the effect of increasing and decreasing upstream input flow (10%, 20%, 30%) on drain operation in 5, 10, 15 and 20 year intervals was simulated. According to results at all time intervals, the greater the upstream inflow, the more solutes are leached out of area by interception drain. The simulation results also showed that the initial soil salinity at the drain flow decreased about 16.1 ds/m after 20 years. As upstream input flow decreases 10%, 20% and 30% this amount (16.1 ds/m) decreases 11%, 17% and 25% respectively. While increasing upstream input flow decreases salinity 22%, 28% and 40% further.