| The log structure in the river channel could form a pressure gradient along the river bed,driving the exchange between surface water and groundwater.In order to explore the impact of log structure on riverbed temperature in different seasons,a three-level log structures across the river were set up on a tributary of the Lushui River in Huangpi District,Wuhan.The temperature sensor were used to track and monitor the temperature changes in different sediments deeps in the upper and lower reaches of the logs.The surface water and groundwater models were established by using the COMSOL Multiphysics software,and the changes in the temperature field of the hyporheic zone under different structural parameters and environmental factors were researched.The main conclusions were as below:(1)No matter whether log structures were set or not,the temperature of the monitored sample points in hyporheic zone gradually increased with the increase of the sediment depth.In summer and winter season,as the depth of the hyporheic zone increases,the temperature amplitude became smaller,the peak of the temperature curve decreased with the increase of sediment depth,and the hysteresis of the peak became more obvious.It also has been indicated that the log structure across the river could reduce the temperature of the undercurrent zone within a certain range.(2)In summer,the average latent flux at the 1-7 sample points were:-86.90L/(m~2·d)?26.69L/(m~2·d)?-30.36L/(m~2·d)?40.65L/(m~2·d)?103.34L/(m~2·d)?155.98L/(m~2·d)?-39.30L/(m~2·d).The average fluxes of 7 samples in winter were:-91.75L/(m~2·d)?57.20L/(m~2·d)?-10.77L/(m~2·d)?118.49L/(m~2·d)?178.19L/(m~2·d)?84.07L/(m~2·d)?-369.18L/(m~2·d).By comparing the groundwater flow diagram obtained by the simulation,it could be found that log structure could change the flow direction of the groundwater within a certain range.In the upper reaches of the logs,the surface water recharged the groundwater,and the downstream recharged the surface water.The monitoring results showed that a positive value in the upstream of the log and negative value in the downstream of the log.It was basically consistent with the field work results.(3)Log structure parameters were changed to explore its influence on the temperature field of hyporheic zone.The results showed that as the log diameter increases,the temperature of the underflow zone gradually decreased while the simulation is completed.Changing the distance between logs,the result showed that with the increase of distance,the buffer zone downstream of the first-level log became significantly larger,the temperature of the buffer zone gradually increased,and the temperature of the second-level log sediments gradually decreased.With the increase in the number of logs,the maximum temperature of sediments downstream of multi-level logs increased from 20.58?to 21.19?.It showed that with the increase of log numbers,the temperature of the downstream of the log structure gradually increases in hyporheic zone,and the temperature buffer area was also increased.(4)The influence of changes in environmental factors on the temperature field of the hyporheic zone were as follows:The increase of water temperature and water depth would caused the temperature contour to move upward,which indicated that with the increase of water temperature and water depth,the temperature of the hyporheic zone gradually increased.With the increase of velocity and bed material permeability K,the temperature contour tended to move downward,which indicated that the temperature of hyporheic flow zone gradually decreased. |
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