The effect of natural and engineered hydraulic conditions on river-floodplain connectivity using hydrodynamic modeling and particle tracking analysis

Hydraulic conditions and water resources management projects can significantly alter river-floodplain connec-tivity, which in turn can alter hydrologic and biogeochemical processes in river corridors. In this study, the hydrodynamics of river-floodplain connectivity under different flood conditions and the effect of the Nanchang Water Resources Project Group (NWRPG) in the middle branch of the Ganjang River were investigated using a combination of two-dimensional hydrodynamic simulations and particle tracking. The hydrodynamic model was calibrated and validated using data from several gauging stations and field measurements. Floods in the Ganjang River can be limited to the river itself ("River Flood", flood with normal lake level) or further extended to the Poyang Lake ("Lake Flood", flood with high lake level). The results show that compared with "River Flood" scenarios, "Lake Flood" scenarios increased the water level flooding a larger area. The flow velocity decreased and the residence time (RT) of particles increased. The particle travel distance (PTD) of "River Flood" was larger than that of "Lake Flood". The larger the flood, the greater the transboundary flux between the river and the floodplain, and the shorter the RT and PTD. The effect of NWRPG was the permanent flooding of part of the river floodplain, causing some habitat loss. Due to the increase in discharge, the implementation of the NWRPG results in a shorter RT with a smaller standard deviation, which has little effect on the PTD distribution. These findings can facilitate river connectivity restoration efforts in the Ganjang River and also provide a reference for assessing the impact of barrage projects.