Analysis of water balance in Baotu Spring basin under two typical boundary conditions
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Abstract:
Accurate understanding of groundwater balance in karst area can provide technical guarantee for scientific evaluation of groundwater resources.To study the water balance in karst area,it is necessary to clarify the boundary conditions and hydrogeological properties of karst water system.However,due to the high complexity of geological structures and karstic development in the karstic area,it has become one of the difficult problems in current research.The Baotu Spring basin is a typical karst basin in northern China.At present,there are two different views on the east and west boundaries of the Baotu Spring basin.If the boundary of the Baotu Spring basin is unclear and its hydrogeological property is unknown,the calculation of water balance in the Baotu Spring basin can not be correctly carried out.The research on the boundary conditions and the water balance of Baotu Spring basin under two kinds of boundary conditions were carried out. The main difference between the east and west boundaries is the area surrounded by the fault and the watershed,and the main recharge is the infiltration from precipitation.According to the actual hydrogeological conditions in the study area,a numerical model is established to simulate the conversion from precipitation to different types of runoff in the faultwatershed area to obtain its water exchange law.According to the obtained conversion law,the water balance method is used to calculate the replenishment and discharge in the study basin,and the water balance results of the two boundary conditions are obtained.On the other hand,based on the same law of water exchange,combining with the exploration data and drilling data of the Baotu Spring basin,the numerical simulation models of faultboundary spring basin and faultwatershed boundary spring basin are established by the FEFLOW software,and the water balance of the two kinds of boundary conditions is calculated.The calculation results provided by the waterbalance method and numerical simulation model are compared and analyzed. Based on the numerical model of the fault-watershed area,the relationship between the precipitation and the proportion of surface runoff (SR/P),the proportion of porous subsurface runoff (PSSR/P),the proportion of karstic subsurface runoff(KSSR/P) can be established.The results provided by the numerical simulation model show that the relation between the proportion of surface runoff and precipitation is RSR=33.967lnP-14.728,the relation between the proportion of karstic subsurface runoff and precipitation is RKSSR=-30.52lnP+59.941,and the proportion of porous subsurface runoff is about 0.50.Applying this law to the waterbalance method,it is found that the replenishment,discharge and balance difference of the faultboundary spring basin are respectively 9.022 million m3/a,3.376 million m3/a and 5.646 million m3/a larger than that of the fault-watershed boundary spring basin.Applying this law to the numerical simulation method,it is found that the replenishment,discharge and balance difference of the fault-boundary spring basin are all greater than that of the fault-watershed spring basin,and the difference values are 12.108 million m3/a,4.433 million m3/a and 7.675 million m3/a,respectively.The precipitation in the fault-watershed region is converted into surface runoff(SR),porous subsurface runoff(PSSR) and karstic subsurface runoff (KSSR) runoff in a certain proportion.Therefore,when the fault-watershed is used as the boundary of the Baotu Spring basin,it is necessary to consider the close hydraulic relationship between surface water and groundwater as well as the transformation relationship between them.Reasonable conversion of the water volume of each part can improve the accuracy of water balance calculation results.Combining with the law of water exchange in the fault-watershed region,the water balance in the spring basin is calculated by the traditional water balance method and the numerical simulation method.The calculation results of the two methods show that the replenishment,discharge and balance difference of the fault boundary spring basin are greater than that of the fault-watershed boundary spring basin.There are some differences in spring water balance under different boundary conditions,but the difference is small.
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