Groundwater Recharge from Precipitation at Chabagou Catchment,Hilly and Gully Region of Loess Plateau

摘要

In the past decades,runoff of the Yellow River has decreased sharply and the downstream even dries up for a long time in a year.At the semi-arid Loess Plateau locating at the middle reaches of Yellow River Basin,people constructed widespread silt arresters and terraces to conserve soil and water resources.However,the origin of local groundwater and groundwater cycle pattern is still under dispute for lack of systematic observation on water cycle.In the study area Chabagou Catchment,a typical Loess Plateau Ravine Region with great human activities,13 rain gauge stations were chosen to sample rainwater and groundwater every month during May and October in 2004-2006,where we also observe the rainfall information automatically.Also,at the Caoping Xigou Station near the outlet,we observed the rainfall information and collect rainwater heavier than 5 mm after each rain event.Also,we performed two times of instantaneous sampling in June and August,2005 at the whole Chabagou Catchment for isotopic and hydrochemical analysis.In combination with rainfall information and isotopic compositions for precipitation and groundwater at Chabagou Catchment,the groundwater cycle pattern are analyzed.the environmental isotopes of groundwater is very steady,and opposite to the obvious seasonal change both in rainfall and its isotopic composition,which indicates that,groundwater get recharge from heavy rain or rainstorm,which is depleted in environmental isotopes,while the rainfall less than 25 mm can hardly recharge the groundwater.The rainwater experiences longterm evaporation and adequate mixing before they reach the water table.The groundwater origins rainfall with isotopic composition of about (-9.93,-71.3).The current result hasn't reflected obvious evidence of surface water recharging groundwater at the 13 stations,and there is no evidence of rapid route for rain recharging groundwater.