Study On Karst Hydrogeological System In Nanjiang Grand Canyon,Guizhou Province

Nanjiang Grand Canyon Scenic Area is located in Kaiyang County,Guiyang City,Guizhou Province.It is a national 4A-level scenic area.Unlike other karst canyons,Nanjiang Grand Canyon has mountains on three sides,its only entrance is like a trumpet.There are many huge rocks in the canyon.The waterfalls in the canyon are well developed.JinZhong Waterfall is the largest travertine waterfall in China.The palm bamboo growing on the cliffs on both sides of the canyon is rare in China and the hydrogeological system is complex.Taking Nanjiang Grand Canyon as an example,this paper studies the karst hydrogeological system.In the process of evolution of hydrogeological system,hydrology and geomorphology interact.Through field investigation and experiment,this paper analyses the hydrogeological characteristics and karst morphology of the study area.Through the simulation of groundwater flow field,the location of groundwater divide and the distribution of groundwater undercurrent are analyzed according to the principle of water balance.On this basis,the time of exploring hydrogeological system is discussed.Spatial variation characteristics and evolution process are discussed,and the influence of internal and external forces on the evolution of hydrogeological system is also discussed.The conclusions and research results are as follows:(1)The study area mainly exposes Cambrian ancient carbonate strata,which belongs to typical subtropical Canyon karst landform.The groundwater in the study area mainly receives atmospheric rainfall recharge,followed by surface water and lateral runoff recharge.The groundwater is mostly phreatic,buried deep and less affected by evaporation and drainage.The upper aquifer is discharged by springs and artificially exploited,and the lower aquifer is discharged by interlayer runoff and dissolution.Pipeline fissure runoff is dominant.(2)The area of carbonate rocks in the area accounts for 76%,and the surface karst morphology is characterized by stone buds,karst ditches,karst troughs,surface karst caves,depressions,falling water caves and travertine;the underground karst morphology of ladder rocks is characterized by karst fissures,caves,etc.On the plane,the karst development degree from SE to NW gradually decreases;the distribution of stone buds,karst ditches and karst troughs is usually linear and zonal,and the top of ladder karst is the most concentrated part(3)The groundwater flow field model established by GMS software shows that the groundwater flow direction is approximately the same as the actual flow direction,and the fitting effect of the flow field is good.The calculation results of water balance show that the groundwater in the area is in a positive equilibrium state.The reasons for the analysis are the shrinkage of underground watershed or the existence of underground deep buried current and karst pipelines.(4)The hydrological characteristics and karst geomorphology of the hydrogeological system vary with the geological structure from the watershed and boundary locations far from the canyon to the canyon area.The formation of Nanjiang Grand Canyon is the result of intense downcutting of rivers and intermittent uplift of the crust since neotectonic movement.In the watershed area far from the drainage base of modern canyon,neotectonic movement has less influence,and is greatly influenced by neotectonic movement in the near shore of the canyon,with strong surface and underground karstification.