Comparative analysis of water-heat exchange characteristics of the riparian zone downstream of dam in different seasons

To compare hyporheic exchange characteristics and temperature field distributions of the riparian zone following dam release in different seasons, we monitored and analysed the water level and temperature of surface water and groundwater downstream of Xin'anjiang Dam using Darcy's law. Results revealed that lateral exchange flux and river water level were in a counterclockwise "rosette" relationship regardless winter or summer, and the exchange intensity was smaller away from the river. Hyporheic exchange intensity and supply way were distinctly different between winter and summer, where the total exchange volume per unit width near the bank was 55.23 m³(week)and 75.08 m³(week), respectively. In addition, longer lateral exchange length and shorter exchange time were observed in the summer. The temperature field of the riparian zone was significantly affected by low temperature fluctuations, and the vertical direction was characterised as "warmer on the surface and cooler at the bottom" in the summer, while in the winter it was opposite. On the other hand, low temperature propagation distance was relatively larger in the horizontal direction and had obvious zonation in the summer. Therefore, in the process of river ecological management of reservoir downstream, the influence of different seasons should be appropriately considered.