The Application Of Isotope Compartmental Mixing Cell Model In Hydrologic Cycle Of Shallow Water In The Overground Section (Henan Section) In Lower Reaches Of The Yellow River

The overground section(Henan section) in lower reaches of the Yellow River is the most concentrated area of cities and population,and the industry and agriculture are developed while water consumption and demand are the largest.But the direct use of the the Yellow River water has many problems such as complex process and high costs.So the quarternary shallow groundwater in the region has gradually become an important water supply of the cities along the the Yellow River,while the water of the Yellow River provide a wealth of recharge to groundwater.However,the groundwater resources were developed irritationally and a series of environmental geological problems occurred,such as a continuous decline in groundwater levels, groundwater pollution,land subsidence,which serious constraint the economic and social development in Henan province.This requires the comprehensive understanding of the hydrologic cycle characteristics in the region,especially the quarternary shallow groundwater as the the main production formation in the overground section(Henan section) in lower reaches of the Yellow River.Isotope techniques is a widely used advanced technology to study the water cycle,the studies of isotopes focus on the qualitative studies and the quantitative studies based on the distributed parameter models,and there is much room for improvement.The mixing cell model used in this paper is a distributed parameter model of isotope.It represents the groundwater system as a network of interconnected cells or compartments through which water and one or more dissolved constituent (tracer) are transported.In a specific cell,the tracer is completely mixed.The application of the model can obtain more detailed characterization of groundwater cycle and quantitative characteristics in each cell. According to the spacial and temporal distribution of isotope samples,the boundary conditions and hydrogeological parameters of partition,the calculation region is divided into 10 cells,where the mixing cell model applied.In the research, the prepare work took into account the balance and momentum fractionation fractionation effect.And a list of equations were transformed into a constrained multivariable function,in order to get the solution of the equations via minizing the function and to carry out the solution via using the optimization toolbox for MATLAB. Then we can calculate the age of groundwater and the groundwater cycle velocity.The main achievements acquired in this study are as follows:1.This paper used a distributed parameter model,the isotope mixing cell model in the research of hydrologic cycle of quarternary shallow groundwater in the overground section(Henan section) in lower reaches of the Yellow River.And the deficiencies of the past research that the neglecting the isotope fractionation in process of evaporation and using one single tracer as as a constraint,were improved. A mathematical model was established and the solution of the model was discussed. By introducing the error term,the solution of simultaneous equations was transferred to the solution of the optimal value function in multi-variable binding conditions. Compared to the solution of equations,this solution can get convergence easier.2.This study got the average humidity of 60%by drawing the groundwater evaporation line.According to the Gonfiantini equation,we got the kinetic fractionation factor,△ε¹⁸O_bl-v= 5.7‰,△ε²H_bl-v= 5.0‰.In accordance with the relationship between water-vapour equilibrium exchange and temperature,we calculated the total fractionation as the calculation time average temperature is 20℃in study area,ε¹⁸O_tatal= 15.4‰,ε²H_tatal= 87‰And then the isotopic values of the vapour is available.The results show that the groundwater recharge is mainly from precipitation, about 50%in areas along the riverside of the the Yellow River,and the proportion of precipitation gradually increases to the north and south from the Yellow River up to more than 70%;the the Yellow River lateral seepage recharge accounted for the total recharge volume of 13.74%in the study area,along the riverside accounting for the proportion of the total recharge of up to 50%;evaporation is the mainly discharge,the proportion of the total discharge is 53.80%,followed by man-made mining,accounting for 34.59%.These results show that the hydrologic cycle in the quaternary shallow groundwater in the study area is mainly vertical,and the lateral runoff is weak.The proportion of the the Yellow River recharge is more than 40%in cell 2 and cell 8;and the proportion of recharge from the Yellow River in the cells abut these two cells reduce one order of magnitude,about 3%-7%,the distance between centroid of these cells and the the Yellow River is less than 20km;the proportion continue to reduce one order of magnitude to 0.3%-0.5%from the the Yellow River.We can see the the Yellow River lateral seepage recharge have a significant impact on the scope of no more than 10km at south bank and 20km at north bank.The the Yellow River lateral seepage volume to the north bank is greater than that of the south bank,for there is no significant difference in the hydraulic gradient,which is indicated the results of previous studies that the hydrologic conductivity of quaternary aquifer of northern cells(K=27m/d)is greater than that of southern cells(K=12m/d).The pumping in Kaifeng area changed the natural groundwater flow field,increased the hydraulic gradient near the south side of the Yellow River,made the lateral seepage recharge from cell 8 to cell 9 is greater than the amount of water recharge from cell 2 to cell 3.3.The age of groundwater is an important feature of the groundwater cycle.The study calculated the age of groundwater in 20 to 47 years,the cells abut the the Yellow River has the smallest,respectively,22.3 and 20.1 years old.From the the Yellow River to the north and south,the age gets larger,fully reflecting the rapid cycle along the riverside area to the north and south on both sides by the weakening affect of the the Yellow River.In addition,the age in the north of the Yellow River is smaller than the southern bank.The age calculated is smaller than the age of isotope tritium, due to diffusion,mixing effects,etc.The study also based on the distance between the centroid of the cells and difference between the age,then calculated the quaternary shallow groundwater circulation speed,the speed of the south bank of the the Yellow River is 816m/a,and 2744m/a at western of the north bank,1258m/a at east.These indicated the cycle speed is faster at north bank than south bank,and the speed of the eastern part is faster than western region.4.The results of the study compared with traditional methods,with good consistency,research proved that the improved mixing cell model was applied to the calculation of underground water,such as is feasible.The isotope mixing cell model have irreplaceable advantages in the request of a certain degree of spatial and temporal precision for its low requirement in hydrogeological parameters,and can supply,and can get the spatial and temporal distribution of characteristics in water cycle,such as recharge,discharge and lateral seepage.