Application Of Ion Tracer On The Law Of Downstream Hyporheic Exchange Of The Dam

The dam is an important infrastructure and the means of water resource utilization and regulation,but at the same time playing a huge benefit,dams will also cause physical,chemical,and so onl changes in the downstream river hyporheic zone at different scales and levels.The main aspects of dam vertical impact are reflected in the dynamic changes of groundwater and surface water.This dynamic change affects the exchange of moisture and solute between surface water and groundwater.Therefore,it is of great value and significance for the protection of river ecology in the downstream of the dam and the health of surface water and groundwater systems in the basin by further understanding of the hyporheic exchange process.The research content and main research results of the paper are as follows:(1)The law of hyporheic exchange was studied under the change of single influencing factors,such as flow velocity v,water depth H,dune wave height h,and the permeability of bed sediment k through the numerical simulation method.The results demonstrated that the flow velocity v,sand dune height h and the permeability of bed sediment k is positively correlated with the degree of hyporheic exchange,and the water depth H is negatively correlated with the degree of hyporheic exchange.(2)The sensitivity of the surface water and groundwater coupling model parameters in the hyporheic exchange process based on the orthogonal test method was analyzed which is by simulating the process of injecting dyes into the sand dunes by syringes and evaluated by the monitor time consumed by the change of the concentration of the point points to equilibrium.The results show that the main influencing factors in the hyporheic exchange process are the flow velocity v and the permeability of the riverbed k.The influence of the flow velocity v is particularly obvious and the permeability of the riverbed sediment k is lower.Secondly,the river bed dune wave height h has a significant influence on the hyporheic exchange process of the sink system.According to the consequence of range analysis,it is concluded that for the hyporheic exchange process of this model that the sensitivity of the influencing factor v is the highest,and the riverbed permeability k is second.and the sensitivity of river bed sand dunes h is greater than that of water depth H.(3)The three-dimensional numerical simulation was carried out and the results shows that due to the pulsating randomness of the turbulence,the y=0.15m section of three-dimensional model pressure and solute concentration distribution will be different compared with two-dimensional.According to the calculation results of water flux on X,Y and Z direction and total water and solute flux at the interface of water and sand,it is concluded that the hyporheic exchange process is mainly on vertical,and the total flux of water and solute on the stoss face is greater than that on the lee side which causes migration and retention of moisture and solute in the river bed.Comparisons were made between the three-dimensional model and the two-dimensional model of the monitoring point solute versus time curve and the results show that the rate of change under the three-dimensional model is slightly larger than that of the two-dimensional model.Compared with the three-dimensional model and two-dimensional model at the monitor point B,the rate of change is faster and then slower.