Assessing morphological changes in a human-impacted alluvial system using hydro-sediment modeling and remote sensing

Construction of managed aquifer recharge structures (MARS) to store floodwater is a common strategy for storing depleted groundwater resources in arid and semi-arid regions, as part of integrated water resources management (IWRM). MARS divert surface water to groundwater, but this can affect downstream fluvial processes. The impact of MARS on fluvial processes was investigated in this study by combining remote sensing techniques with hydro-sediment modeling for the case of the Kaboutar-Ali-Chay aquifer, northwestern Iran. The impact of MARS on groundwater dynamics was assessed, sedimentation across the MARS was modeled using a 2D hydrodynamic model, and morphological changes were quantified in the human-impacted alluvial fan using Landsat time series data and statistical methods. Changes were detected by comparing data for the periods before (1985–1996) and after (1997–2018) MARS construction. The results showed that the rate of groundwater depletion decreased from 2.14 m/yr before to 0.86 m/yr after MARS construction. Hydro-sediment modeling revealed that MARS ponds slowed water outflow, resulting in a severe decrease in sediment load which lead to a change from sediment deposition to sediment erosion in the alluvial fan. Morphometric analyses revealed decreasing alluvial fan area and indicated significant differences (p < 0.01) between pre- and post-impact periods for different morphometric parameters analyzed. The rate of change in area of the Kaboutar-Ali-Chay alluvial fan changed from ?0.228 to ?0.115 km²/year between pre- and post-impact periods.