Study On Relationship Between Groundwater Hydrodynamic Field Evolution And Geological Disasters In Hei Fangtai Irrigation Area

To reduce the rise of ground water level caused by infiltration of irrigation waterand prevent geological disasters such as landslide caused by the rise of ground waterlevel in Heifangtai Terrace, Gansu provincial department of land resources and otherrelevant units carried out the―Pilot Project of Heifangtai Terrace Like Plain LandslidePrevention, Drainage and Groundwater Exploration‖. This paper is based on theproject. Firstly, the data of meteorology and hydrology, physical geography,topography and landform, formation lithology and hydrogeololgy in the research areawere fully collected. Secondly, the hydrogeological conditions and characteristics ofunderground water in the irrigated area of loess terrace like plain were figured out bysystematic arrangement and analysis after carefully referring to t he existing materials.Thirdly, taking the numerical simulation of underground water as the theoreticalevidence, a three-dimensional numerical model of underground water based onProcessing MODFLOW was built. The model was identified and corrected to obtain theoptimum parameter. The relationship between the evolution of groundwater dynamicfield and the geological disasters in time and spatial scale was analyzed. Under theguidance of the theory, we thought human disturbance as the effective way to preventgeological disasters and selected shaft drainage works as the preventive measure.And we use numerical model for predicting groundwater dynamic field change underdifferent shaft drainage scheme to provide a scientific basis for prevention effect of theshaft drainage works in the study area on geological disaster. This paper mainlydraws conclusions as follows:(1) Through analyzing the characteristics of the internal water layer in the research area,we confirmed that the internal water layer of the research area mainly consists of Malan loessphreatic aquifer of the Quaternary system Pleistocene series and pebble pressure bearing ofthe Quaternary system Pleistocene series--unconfined aquifer, and determine that the powderclaypan of the Quaternary system Pleistocene series belongs to aquiclude. (2) The main supply items of the underground water of loess formation in the researcharea include rainfall infiltration recharge, field irrigation infiltration recharge and canalseepage recharge, and drainage items mainly consist of crossflow drainage and springdrainage. In the area, the71.6%of annual supply amount of underground water of the loesslayer is from irrigation infiltration recharge. The pebble bed is the bearing course--cross flowis the main supply, and spring is the discharge.(3) On the ground of fully understanding hydrogeological conditions and characteristicsin the research area, and taking GIS technology as the guidance, to build the space structure ofaquiclude in the research area, on this basis, to utilize Process MODFLOW software to build athree-dimensional numerical model of underground water flow in the research area. To makeuse of the fitting between the measured value of observation wells and the calculated value ofmodels, the tendencies of water level variation of the two are in substantial agreement. Allabsolute average errors meet the required precision of fitting, and the overall tendencies ofcalculated flow distribution and measured flow distribution are the same basically, with afavorable fitting effect. Therefore, the model has certain simulation properties.(4)The evolution of groundwater dynamic field with time and the uneven distribution ofgroundwater dynamic field in space are the main cause of initiating geologic hazards. Wecan reduce the rise of ground water level by human disturbance.(5) Based on the long-term observation data of loess-and-pebble mixing wells, designthree different layout plans for the shaft drainage project. Among three different layout plansfor the shaft drainage project, to predict the flow distribution of underground water of themodel after operating for5years and10years. To determine the maximum cone ofdepression and cone radius at the end of5years and10years of different plans, and analyzethe duration curve for water level of the representative well.(6) We suggest that using the water-saving irrigation to reduce the supply ofthe aquifer in order to reduce the thickness and the water table of the loess unconfinedaquifer.