The Effect Of Soil Texture And Structure Of Vadose Zone On The Recharge Of Groundwater

Ordos Basin, with abundant mineral resource, is one of the important energy bases in ourcountry. Because of the sparce precipitation, strong evaporation and shortage of surface watersources, groundwater has become the most important source of water supply for industry andagriculture. But located in the arid or semi-arid area with vulnerable ecological environmentin this area, effective management of groundwater resources is imminent to be carried out.Foregone research shows that vertical exchange is the chief way of water cycle in the area.Atmospheric precipitation is the main recharged source, which accounts for96.01%in totalwhile discharge is mainly evaporation, which is as much as62.56%. Therefore, recearch onthe recharge of phreatic water is essential to realize the rational development and utilization ofgroundwater resources in Ordos.Layered structure is ubiquitous in the nature due to the action of wind, geologic forces andso on. In view of this natural phenomenon, in accordance with the situ test data, based on thetheory of saturated-unsaturated flow, this paper is completed by using the method ofmathematical simulation to analyse the main influence factors of the groundwater recharge.The results show as follow:1、Based on the test data of the comprehensive profiles of moisture and salt contentmigration of the vadose zones in-situ in the Ordos basin, it shows that:(1) Moisture migrationof vadose zones can be roughly divided into three zones, Ⅰ、the positive exchange zone ofsoil-atmospheric moisture (0~0.8m), Ⅱ、the transition and regulatory zone of moistureinfiltration (0.8~3m) and Ⅲ、the moisture conduction zone (from the depth of3m to thephreatic surface).(2) When there exists sandy zone in upper vadose zone, the total waterpotential is big-end-up; when there is sandrock or clay-zone in upper vadose zone, the zeroflux plane (ZFP) is formed.(3) Heterogeneous interface of vodase zone can cause deflectionof potential line section, resulting bending and even the emergence of ZFP. The more storeysof vadose zone and the larger diversity of the conductivity between two layers, the greaterbending degree of the potential curve. And there may engender a plurality of ZFP.2、The numerical relationship between atmospheric precipitation (evaporation) and thedynamic of groundwater level approximatly obeyed Poisson distribution under the conditionof neglect of the artificial exploitation and lateral recharge (excretion).3、The more rainfall, the more supply quantity that groundwater gain. For example, when yearly precipitation is376mm,407mm and446mm, the supply is184mm,207mm and241mm respectively if the lithology of vadose zone is weathered sandstone. Differentlithology causes different recharge, the order is aeolian sand>sand (Salawusu Fm)>weathered sandstone>silty sand under the condition of same precipitation and depth ofgroundwater.4、The recharge can be calculated from multiply coefficient by precipitation only if theentire water dropped into the vadose zone transform into groundwater. In the local climate(95%year of precipitation frequency), the method can be used for aeolian sand within thedepth of19m. For sandy soil (Salawusu Fm), weathered sandstone and silty sand, thecorresponding depth is15m,12m and10m respectively.5、The soil water potential is continuous but the moisture content is mutational if layeredstructure. Fine grains under coarse grains is conducive to rainfall infiltration, however,layered structure of vadose zones with coarse grains under fine grains is converse.