Study On Groundwater Circulation And Renewability In The Taiyuan Basin

The groundwater system in the Taiyuan basin is very complex.Human activities had substantially changed the characteristics of groundwater occurrence and circulation,and caused many environmental and geological problems,such as regional decline in groundwater levels,groundwater quality deterioration and the formation of depression cones.Study on groundwater circulation and renewability can help manage groundwater utilization and promote the sustainable use of groundwater in the Taiyuan Basin.On the basis of understanding of geological and hydrogeological conditions,the method of groundwater hydrodynamics,groundwater chemistry and environmental isotopes have been used to study the recharge source and flow regime and to evaluate pore groundwater renewability.The study mainly emphasizes on three aspects:?1?Groundwater ages were determined using multiple isotopes and the groundwater age structure was established.Groundwater is relatively young in most of the piedmont area.Two high-age zones?with ages>20000 a?exist in the center of the plain,One is located in the south of Qingxu,and the other is located in Fenyang.And the distribution of the high-age zones was near the groundwater depression cones.The reasons of this phenomenon:Powerful driving force by exploitation causes the groundwater flow to the depression area;the exploitation of medium-depth groundwater cause the leakage recharge from deep old groundwater.?2?Groundwater recharge source and mechanism in the basin were identified,and recharge ratio are calculated in some representative area.The main recharge sources of shallow groundwater are precipitation and lateral inflows,and some local areas are influenced by surface water infiltration.The medium-depth groundwater is mainly recharged by lateral inflows of karst groundwater and fissure groundwater from mountain area,leakage shallow groundwater and groundwater from bottom fissure system.The deep groundwater is mainly recharged by lateral inflows of karst groundwater from mountain area.?3?The flow regime was delineated and the interaction between aquifers is explained.The flow direction of shallow groundwater is controlled by the terrain,and groundwater moves laterally from the edge to the center of the basin,and from north to south.The medium-depth groundwater flows from the edge toward the depression cones and several groundwater watersheds had formed.Vertically,the groundwater flows from shallow aquifer and deep aquifer to medium-depth groundwater especially in depression areas.?4?The influence factors of renewability were analyzed and the renewability was quantitatively calculated,and the sedimentary basement is a very important factors.The renewal rates of most shallow groundwater are less than 3.5%a^-1.The renewal rates of medium-depth and deep groundwater are less than 0.1%a^-1.The shallow groundwater and medium-depth groundwater can be exploited properly,but the deep groundwater is not suitable for exploitation.