Modeling Surface and Ground Water Hyporheic Zone Using MODFLOW, MT3D and RT3D Models

Hyporheic zone is an active area that groundwater and surface water are mixed together in that zone. Any existing contamination in the surface water can be transferred to groundwater through this zone. In this research, the hyporheic zone beneath Zarjoob River and above Foomanat Aquifer was investigated by modeling to understand the impact of river on groundwater quality. For this purpose, three stations and three nearby groundwater wells were selected and water samples were collected in Year 2006-2007. The hyporheic zone was modeled for TDS as conservative parameter and NO3 as non-conservative parameter. MODFLOW and MT3D were used to simulate TDS in the hyporheic zone in two seasons; the agricultural season and non-agricultural season. The results showed that the hyporheic zone in non-agricultural season is 20 m far from the river, while in the agricultural season it was significantly less than 20 m. The results also showed that the reduction rate of TDS in agricultural season was more than that in non-agricultural season. This could be due to more groundwater use and increase in groundwater flow velocity. In the next step, NO3 was simulated using MODFLOW and RT3D. The simulation was carried out for two scenarios; with and without biodegradation. The results showed that without considering biodegradation, the hyporheic zone would extend to 25 m far from the river while with biodegradation it would be reduced to 20 m.