Research On Water Yield Property Assessment Of Karst Groundwater Based On GIS

The water yield property of karst groundwater in Litang region of Guangxi Province was evaluated quantitatively, combined spatial analysis of GIS, geostatistics method and nonlinear model. The evaluation result reflected the enrichment regularity of karst groundwater and its relation with influence factors, enhanced the precision and accuracy of karst groundwater yield property evaluation, covered the shortage that karst groundwater yield property couldn't be analyzed quantitatively before, and provides theoretical method and technical support for the quantitative evaluation of karst groundwater yield property.Firstly, the database model of karst groundwater yield property evaluation in Litang region was constituted based on spatial database model, i.e. Geodatabase, and formed a complete evaluation database system. This model has three layers: database, feature class and feature, includes seven datasets, such as geography dataset, geologic structure dataset, hydrogeology dataset, flow field dataset, assistant dataset, grid dataset and table dataset. Each dataset is composed of many feature layers of point, line and polygen, and each feature layer contains attribute data.Secondly, the vertical distribution regularity of subterranean karst was seized, and the water yield property in karst aquifer was zoned.Caves exposed by drilling can be divided into five layers according to the elevation: 100~85, 85～75, 75～55, 55～45 and below 45m. The karst development intensity first strengthens then weakens gradually with depth increasing. Subterranean karst has vertical zonation, and formed three main karst development belts, the elevation is above 85m, 85～45m and below 45m respectively, of which karst development belt in 85～45m is the intensest development belt of subterranean karst in the research area, which controlled the enrichment regularity of karst groundwater. The water yield property of karst aquifer is divided into three belts according to water enrichment degree: seasonal fluctuation abundant groundwater zone, strong abundant groundwater zone and weak abundant groundwater zone. Thirdly, the spatial distribution regularity of karst in the research area was analyzed quantitatively with geostatistics method.Subterranean karst development in the research area is anisotropic, unevenly distributed in space, and has evident dominant direction, which is NE 42.6～46.7°. Subterranean karst distributes strippedly in space, and has three karst development belts, which directions are NE30～50°, of which karst in middle belt develops intensely. Subterranean karst is controlled by joint fissure which strike is NW0～30°and fault tectonic which strike is NE45～60°, which makes the direction of subterranean karst development inconsistent with the strike of fault tectonic, the included angle of which is 15～20°. Subterranean karst has the property of concentrated development, which centralizes in two sides of fault tectonic.Fourthly, the karst groundwater enrichment in Litang region was evaluated quantitatively with GIS.The impact of six influence factors such as karst development degree, fault structure, subterranean stream system, type of geomorphy, stratigraphic association type and groundwater level amplitude on karst groundwater enrichment was analyzed quantitatively, the influence weight of them was determined, and karst groundwater enrichment evaluation model was constituted, which was used to the quantitative assessment of karst groundwater enrichment in Litang region.Karst groundwater in the research area distributes strippedly, and the enrichment regularity is controlled by fault tectonic, joint fissure and subterranean stream system. The distribution of karst groundwater in strata with same lithology is nonuniform, in fault structure position, subterranean stream development place, karst development position, runoff area of groundwater, and region where groundwater level varies with small amplitude, the water yield property is very strong.Finally, the inversion model for relation between pixel value of water enrichment evaluation result image and water yield of borehole was established using nonlinear model, thus the water enrichment evaluation result was quantified, and the distribution regularity of water yield in the research area was calculated.Two kinds of nonlinear model were constituted, one is ordinary nonlinear model, and the other is BP neural network model.The distribution of water yield in the research area is controlled by subterranean stream system, fault tectonic and karst development degree, in areas where subterranean stream system develops, fault tectonic concentrates and karst develops intensely, water yield is relatively large and water yield with high value distributes concentratedly.