Model Study On Coupling Between Groundwater And Evapotranspiration

Evapotranspiration, which includes plant transpiration and soil evaporation, has aclose connection to groundwater depth. At the same time, evapotranspiration stronglyinfluences the distribution and movement of groundwater. As a result, study oncoupling between groundwater and evapotranspiration gives theoretical and praticaldirection for analyzing land surface hydrological cycle, evaluating regional waterresources and coordinating the relationship between social and ecological water use.A mathematical model of unconfined flow toward a discharge well withredistribution of groundwater evapotranspiration is developed. Analytical solutions ofgroundwater level and travel time are obtained. For a typical hypothetical example,these solutions perfectly agree with the numerical simulation results based onMODFLOW and MODPATH. A mathematical model of steady radial flow toward agroup of wells considering recharge and evapotranspiration is developed. The wellfield is simplified by a circular area with uniformly distributed pumpage. Analyticalsolutions for three cases with low，medium and strong pumpage are obtained, whichsufficiently agree with a numerical model. Runge-Kutta solutions of using nonlinearevapotranspiration formulas are presented and compared with the analytical model.They predict almost the same water table distribution and similar redistributionpatterns of evapotranspiration.Based on the data of groundwater level in Ordos Plateau, a concept model whichinterprets the dynamic characters of groundwater is built. The parameter sensitivityand climate sensitivity are analyzed. Among them, Dmax and mainly change theaverage of groundwater depth while mainly changes the amplitude of groundwaterdepth. Then, dynamic superimposed models of a pumping well, large-diameter welland a group of wells are built separately. Based on MODFLOW，the numericalsimulation results show that pumping changes the average, amplitude and phase ofgroundwater level. Furthermore，the magnitudes of the changes are mainly controlledby the distance to the well and the type of the well.The concept models of lakes locating in unconfined aquifer and leaky aquifer are developed separately. In arid areas, precipitation and evapotranspiration are mainsources of lakes, so lakes are considered as large-diameter wells in the numericalsimulation. The results show that the change of aquifer settings takes little effect on thedistribution of groundwater. Then, a model of a large-diameter well capturinggroundwater evapotranspiration is developed and compared with the lakeevapotranspiration model. These two models perform similarly in general，but thesignificant differences in water volume lead to different characteristics of groundwaterdistribution.In this study, a survey of the depth-dependent temperature and electricconductivity was carried out in the typical salt lake: the Sumu Barun Jaran. Spatialdistributions of temperature and salinity are investigated. Abnormal low TDS zonesdeveloped in the water body near the lake bottom which seem to be influenced bygroundwater and indicate concentrated discharge of groundwater into the lake. Further,a coupling model between desert lakes and groundwater flow is developed. Thesimulation method of lakes is discussed and the character of groundwater flow field isanalyzed. On the whole, groundwater flows from southeast to the northwest.