Numerical Simulation Of Karst Groundwater In Huixian Wetland

Huixian wetland is located in Yanshan District,Guilin City,Huixian town and Sitang township of Lingui district.It is composed of many rivers,lakes,ponds,swamps and other water bodies.It is a lake wetland with important ecological value and is known as the"kidney of Guilin".In recent years,affected by climate change and human reclamation activities,the wetland hydrological process is seriously disturbed,and the wetland shows obvious degradation and atrophy.In the 1950s,Huixian wetland also distributed intensive lakes,rivers and streams,with an area of about 25km~2.But now most of them have been developed into fish ponds,farmland or wasteland,with an annual water area of less than 6km~2,and the wetland degradation trend is still continuing,so it is urgent to take effective management and restoration measures.The supply water source of Huixian wetland mainly comes from karst groundwater,and the maintenance of wetland function ultimately depends on the maintenance of karst groundwater hydrological process.However,at present,the karst hydrological research of Huixian wetland is relatively lagging behind,which can not meet the needs of wetland protection.Therefore,the study of groundwater hydrological process in Huixian karst wetland is of great significance to understand the causes and mechanism of wetland degradation.On the basis of collecting the data of physical geography and hydrogeology of Huixian karst wetland,through the analysis and correct understanding of the basic conditions of the study area,the boundary conditions,water-bearing medium structure,supplement,diameter and discharge conditions of groundwater system in Huixian karst wetland area were reasonably generalized,the hydrogeological conceptual model of Huixian wetland research area was constructed,and the hydrological process of groundwater was qualitatively described.The complex hydrogeological conditions of Huixian karst wetland was generalized by using equivalent continuous medium and visual MODFLOW software establishes a three-dimensional numerical model of groundwater in Huixian karst wetland.After identification and verification,the certainty coefficient of measured water level and simulated water level is more than 90%,indicating that the fitting degree of groundwater level was high,and the setting of boundary conditions,source and sink terms and hydrogeological parameters in the model was basically reasonable.Then,the dynamic change of groundwater in Huixian wetland was quantitatively simulated and predicted by the corrected numerical model.According to the calculation of zone budget,the total recharge of groundwater in the simulation period is 442.73million m~3/a,of which 76.85%is rainfall infiltration.The total discharge of groundwater is 427.23 million m~3/a,and the exploitation and evaporation of groundwater account for33.86%and 36.63%respectively.The recharge of groundwater in the simulation period is greater than discharge,which is in a positive equilibrium state.However,in the negative equilibrium state,the dry months account for 2/3,and the total negative equilibrium amount is 44.68 million m~3/a,which indicates that the degradation of Huixian wetland directly affects the regulation and storage function of the wetland,resulting in the phenomenon of"excessive drought in the drought period and excessive flood in the flood period".The results show that the groundwater dynamic changes in the study area are relatively stable under the current mining conditions,and the maximum drawdown in the fifth and tenth years is 6.37m and 5.15m respectively after the continuous increase of 10%of the mining volume.It can be seen that the change of groundwater level in wetland has potential risks threatening the healthy development of wetland ecology.There is no stable supply water source in Huixian wetland.In the case that the natural water inflow is difficult to meet the ecological water demand of the wetland,the corresponding engineering measures can be used for flood storage and water replenishment as well as the retention measures to introduce external water,so that the degradation of the wetland can be alleviated to a certain extent.