Analytical Model Of Transient Temperature Field Based On Temperature Tracing

It is an important engineering guarantee to support regional economy to coordinate development,reduce or avoid flood disaster and realize optimal allocation of water resources.However,the river is a dynamic and highly open non-equilibrium non-linear compound system.The dam construction will not only cause stress to the downstream ecological environment,but also to a certain degree the dynamic exchange between surface water and groundwater in the hyporheic zone of riverbed.So understanding and mastering the hyporheic exchange process and ways for assessment of water resources development and utilization,and to maintain ecological health is of great significance.As a new and efficient analytical method,temperature tracer method has unique advantages for the study of the moisture exchange problem in the hyporheic zone,and it is helpful for the quantitative research on the hyporheic exchange process mode on a broader spatial scale.Therefore,this article combined with,the actual data,through solving a one-dimensional analytical model of the transient temperature field and build two-dimensional seepage field and temperature field coupling numerical model,the calculation and analysis the vertical hyporheic exchange characteristics of the study area,based on this,the influence of the heterogeneity of the permeability coefficient on the calculation results of each analytical model was investigated.Finally,the parametric sensitivity of one-dimensional transient temperature field analysis model is analyzed by orthogonal test method.The main research contents and results are as follows:(1)The time-space variability of hyporheic exchange is affected by the heterogeneity of sedimentary layers and the surface water level.When using a one-dimensional analytical model of the transient temperature field of vertical seepage velocity is calculated,the hyporheic zone with heterogeneity and surface water level fluctuation influence,for shallow temperature measuring point,amplitude-phase group method results variation degree,the largest amplitude ratio method and to minimum phase shift method;For deep temperature measurement,the variation degree of all three methods is small.Among them,the shallow temperature measuring point,because of the influence of the thermal diffusion effect,the amplitude ratio method of the calculation results and its change trend in most of the time difference is small,only in the velocity peak will be different,and the overall results of the calculation of phase shift method change law is relatively consistent,but numerical calculation results have a certain difference,For the deep temperature measurement points,the thermal dispersion effect has the least influence on the calculation results of the amplitude-phase method and the biggest influence on the calculation results of the amplitude ratio method.In addition,it is found that the accuracy of the calculation of groundwater velocity is higher than that of the amplitude ratio method by using phase offset method in the deep measuring point area.(2)By building a saturated two-dimensional seepage field and temperature field coupling numerical model,and correction of the model by the measured temperature data constraints,the vertical seepage velocity inversion of the study area,the results show that the hyporheic exchange of spatial variability in a vertical direction,vertical seepage velocity and surface water level fluctuation has certain response relationship.At the same time,from the analysis of a single influencing factor,we can see that in the shallow temperature measurement point,both the heterogeneity of permeability coefficient and the fluctuation of surface water level will bring greater errors to the results of amplitude ratio method,phase shift method and amplitude-phase combination method.In contrast,ignoring the difference between the positive and negative values of the calculation results,when the heterogeneous permeability coefficient or the surface water level fluctuations,the use of the amplitude ratio method to calculate the vertical seepage velocity of the hyporheic zone has the highest accuracy,amplitude-phase combination The calculation accuracy of the method is secondary,and the accuracy of the phase shift method is the worst.(3)The parameter sensitivity analysis of Hatch analytical model and McCallum analytical model shows that the height difference of temperature measuring point has the greatest influence on the calculation accuracy of the analytical model,followed by the basic physical properties(such as density and porosity)of the solid phase of porous media;Thermal state parameters(such as mass heat capacity,thermal conductivity,and thermal dispersion coefficient)of the solid phase of porous media have little effect on the analytical accuracy of the analytical model.