Study On Karst Water Cycle Evolution Law In Heilongdong Spring Area

Heilongdong spring area is located in the southwest of Handan City,Hebei Province.It is one of the representatives of karst springs in the north.The spring area provides high quality water for the life of local residents and the development of industry and agriculture.Taking the karst water in Heilongdong spring area as the research object,this thesis systematically studies the geological and hydrogeological conditions of the spring area,analyzes the chemical evolution law of the karst water in the spring area,and carries out the genetic analysis,establishes a multi-scale and multi-medium hydrogeological model,simulates the movement law of the karst water in the spring area,and puts forward the countermeasures for the sustainable utilization of the karst groundwater in the spring area of Heilongdong.The main results of this study are as follows:(1)Karst development and characteristics of karst flow field.The pumping data of 113boreholes in the spring area were collected and analyzed,and the karst development law in the spring area was obtained.The karst development weakened with the increase of limestone burial depth.According to the analysis of long-term observation data of karst water level and precipitation observation data,the change of karst groundwater level with atmospheric precipitation is about one cycle every ten years.By analyzing the change characteristics of karst groundwater flow field since the 1970 s,it is concluded that the change of groundwater flow field is greatly affected by human activities.(2)Chemical distribution characteristics of karst water.According to the hydrochemical data in different periods,and with the help of Piper three-line diagram analysis,it is concluded that the hydrochemical types in the northern and southern runoff zones with good runoff conditions are mostly HCO₃-Ca·Mg and HCO₃-SO₄-Ca·Mg,while in the eastern part of Gushan,with the increase of the depth of Ordovician limestone roof,the karst development is weakened,and the hydrochemical types change to SO₄·Cl-Ca and Cl·SO₄-Na·Ca.Coal mining leads to complex karst hydrodynamic conditions,resulting in more mineral dissolution,Ca,Mg ion content increased,sulfate more dissolved in water,resulting in increased salinity in water.Trace elements were tested for the sampling of karst water system.Through the analysis of the spatial distribution characteristics of trace elements,it is concluded that the spatial distribution characteristics of trace elements are highly correlated with spring runoff conditions,and the ion exchange effect is strong in the regions with fast groundwater flow rate and high karst development degree.(3)Study on cycle of karst water.According to the principle of mass conservation after tritium isotope enters the groundwater,the karst water cycle period is calculated to be 17?85 a,and it is analyzed that the groundwater renewal rate in the recharge area is the fastest,followed by the runoff area,and the discharge area is the slowest.(4)Simulation of karst water motion law.Based on the analysis results of hydrogeological conditions in Heilongdong spring area,the hydrogeological conceptual model is established,and the groundwater numerical model is established with Visual MODFLOW to simulate the movement law of karst water.The numerical simulation method and equilibrium method are used to calculate and analyze the water resources,and the recoverable amount of karst water is 210.86 million m³/a.(5)Research on sustainable development and utilization of karst water resources.The water demand of different water use types in different administrative regions of the spring area is predicted.The water demand in 2030 and 2040 is greater than the available water supply of karst water.The optimal allocation of water resources is carried out,and the multi-objective water resources optimal management model is established.The results of optimal allocation of water resources are obtained.Combined with the hydrogeological conditions of the spring area,the measures for sustainable development and utilization of water resources are put forward.The innovation of this thesis is based on the hydrochemical monitoring data of long time series,which clarifies the hydrochemical evolution law of karst groundwater in spring area.By studying the hydrochemical characteristics of trace elements in karst groundwater in spring area,the movement law of karst groundwater in spring area is revealed.The partition of infiltration coefficient in recharge area of spring area improves the accuracy of parameters,and establishes the hydrogeological conceptual model and numerical model of spring area.