Research On Geological Structure Control Of Groundwater Distribution In Bedrock-fissure Aquifers And Implications For Groundwater Exploration In The Middle And Upper Reaches Of Dawen River Basin

The Dawen River Basin is located in the hilly area of central and southern Shandong Province.With the rapid development of society and economy in recent years,the contradiction between groundwater supply and demand in the region has gradually increased,and the problem of natural resources shortage and environment constraints has become more and more apparent.The proportion of bedrock-fissure groundwater in regional groundwater exploitation is higher and higher.Geological structure is the dominant factor controlling the buried condition,distribution and movement of bedrock groundwater.Therefore,it is of great practical significance to explore new groundwater sources,improve the rate of digging wells for groundwater production in bedrock mountain areas,ensure the safety of water supply for people,industry and agriculture,and better protect groundwater resources in the protection areas.From the perspective of the combination of structural geology and hydrogeology,this research was conducted using data collection,field observation and theoretical analysis to investigate the control of geological structures on bedrock groundwater including the macro-basic conditions for the accumulation of groundwater and water conduction mechanism of different structures or groundwater enrichment mode in bedrock areas.Bases on which the potential places for groundwater exploration in bedrock mountainous area were suggested.The main conclusions of the study were showed below:(1)The coexistence of fault block uplift and fault block depression in the middle and upper reaches of Dawen River basin had strict control over the distribution,movement and enrichment of bedrock groundwater.The central part makes a "centripetal" movement.(2)The distribution of water-bearing rock groups is controlled by geological structure,which is the basis for the occurrence of groundwater in the bedrock.The carbonate fissure karst water-bearing rock groups in the area are monoclinic structures,and the bottom part of the Cambrian Zhushadong group directly overlies the Archean metamorphic rocks,affected by the geological structure,this group of karst was developed and has abundant groundwater recharge,forming a typical "layer-like" karst water storage structure,which is an important water supply target layer in the area.(3)The Paleogene Zhujiagou formation conglomerate water-bearing rock group was distributed along the basin-controlled fault in the northern part of Laiwu and Dawenkou basins.The occurrence and movement of groundwater are strictly controlled by the structure and have the characteristics of rich water similar to that of karst water.This finding provides new ideas for the exploitation of bedrock groundwater in the area.(4)The geological structure controls the development range and intensity of the karst of the carbonate rock.The development directions of the karst in the area were mainly along the two twisted surfaces of the NE and NW faults.(5)The key point of groundwater exploration in the bedrock of this area is to find the water-storage structures and water-blocking structures.The mechanical properties and later period activities of the structures are the most important factors that affect the success of groundwater exploration in mountainous areas.In the NW direction,the tensile faults in soluble or brittle rocks are easy to form the water-storage structures with the features of good storage and permeability;While faults in the NE and EW directions have relatively poor water content and permeability,which are mostly have water-resisting properties,and easy to form the water-resistant storage structures.