| Leizhou peninsula is the most serious drought and water shotage regions in the Guangdong Province, but also is rich in groundwater. Some geological environment problems (Such as sea water intrusion, karst collapse, ground subsidence) highlights the groundwater resource did not get reasonable development and utilization of malpractice. Therefore, it is very important to investigate groundwater storage conditions, characteristics of groundwater fluctuation, groundwater circulation pattern, and the rational exploitation of groundwater resources in Leizhou Peninsula. It is very significant in practical and theory not only for effective development of groundwater resources, protection of groundwater environment, but also for the Leizhou Peninsula sea water intrusion prevention.Through the collection of Leizhou peninsula area of geology, hydrogeology and groundwater dynamic monitoring data, underguiding of groundwater system theory, based on hydrogeological fundmental theory, groundwater dynamic theory and Hydrogeologic chemical theory, using groundwater numerical simulation technology and three-dimensional geological modeling, on the Leizhou Peninsula groundwater recharge runoff drainage of groundwater, groundwater circulation pattern and optimization of exploitation and their relevant problems are studied, the main achievements are as followings:1. Based on the2327borehols, combined with the lithofacies palaeogeography, the impact of crater or volcano formation on the stratigraohic structure in the studied area has been studied and the structure of the aquifer model is established.the chracteristics of aquifer are:the burial depth of the shallow water varies from30m to50m, is consist of loose rock pore water and all the volcano rock cave fissure water, widely distributed in the study area, except for the coastal and brackish water areas. Intermediate confined aquifer water is widely distributed in the study area, it becomes thinner or vanishes as the depth of the volcanic rocks increase in the basalt platform region. The north part of Leizhou Penisula is mainly consisted of sandstones of Zhanjiang group, in the South part of Leizhou Penisula, the Zhanjiang group becomes thinner and gradually transition to the upper group of Xiayang group. Deep confined groundwater almost distributed throughout the region, is only lack of in the northwest corner and the northeast corner of the bedrock buried depth. Lei north from under the ocean group segments, to the south of transition for the thunder under the ocean group upper part the first rock group and part of the second rock group.2. According to the observation data of groundwater water table, and the situation of development and utilization of groundwater resource in Leizhou Penisula, the characteristics of groundwater flow field are studied, the impaction of volcano cater on groundwater flow pattern is studied. It is recognized that groundwater flow field is mainly affected by the hydrogeological conditions, groundwater exploitation mode. The mainly characteristics are as followings:(1) Shallow aquifer is easy to accept the precipitation and surface water infiltration, and is not concentrated mining, hitherto unreported form regional drawdown funnel, the flow patterns affected by topography, the ground water table contour is similar with terrain contour. Groundwater runoff overall from northwest to Southeast. Groundwater table is only seasonal fluctuation, the yearly amplitude is generally2-3m, all most above sea level.(2) The groundwater flow field in the middle confined aquifer has a gradual evalution from natural flow field to artificial exploitation flow. Original condition groundwater flow is generally from northwest to Southeast. Due to the concentration of a large number of exploitation, the groundwater level continued to decline, the central region descend funnel has been formed, the area with groundwater level drop2m is1946km2, funnel center water level is-21.95m. groundwater level is above sea level2-5m in very few of offshore area, the reast offshore area are below the sea level.(3) The groundwater table in deep confined aquifer is drawdown continuously since the concentrated mining groundwater in1970s; the area of ground water drawdown is greater than2m already amounted to2315km2, the groundwater level in funnel center is-19.68m. the groundwater level changes in different layers is from shallow to deep, change rate increase, funnel area increase.3. hydraulic features of the artesian well and spring are analysized, and the numerical methods for modeling artesian flow and soring flow are investigated. An example is designed to test the methods.4. Based on the Leizhou Peninsula3-D aquifer structure model, and the combination of hydrology, meteorology, and all kinds of test data analysis and groundwater dynamic data, a groundwater numerical model is built by using seepage-pipe flow model theory, which taking multilayered pumping well and artesian springs into accounted in the model. the MODFLOW software is modified to realize the calculate the multilayerd aquifer and artician springs flow.5. The groundwater recharge and discharge time in the volcano area is calculated by the groundwater numerical model. The results show that groundwater age in the first aquifer is smaller than the one in the second aquifer, and this is consist with tisotope results. the main reason is that there is an aquifuge between the first and second aquifer, and aquifuge thickness is large. At the same time that the first MODPATH aquifer flow acquisition time is about1-2years, while the second aquifer groundwater capture time is6years, groundwater age in the second aquifer is greater than the one in the first aquifer.6. According to the Leizhou peninsula area of groundwater exploitation and potential demand, two kinds of development programs are designed. The programs were predicted and compared by using the numerical model. The results shownthat:for the program based on the exploitation amount, increase by20%yearly, if this amount watwe is all exploited in Chikan, Xiashan and Potou resource area, then in2015will appear the over-extraction phenomenon. Thus programming exploitation amount layout, in addition to the3water sources in accordance with the calculation of the exploiting, the lack of part according to the row in the Puzai and Taiping water exploiting g supplement, and expand the supply of surface water groundwater insufficient ability as part of the supplementary. If groundwater is exploited for downtown or in situ industrial use from the three groundwater exploitations-Puzai, East Island and Taiping-respectively in2015and2020, a secondary cone center will be formed, three forecasting groundwater level superposition will arise at the same time. In2015, the groundwater level superposition in Puzai will be14.88m, in Dongshan it will be9.37m, in Taiping it will bw13.25m; in2020the forecasting groundwater level will drop a little, the groundwater level superposition in Puzai will be15.63m, in Dongshan it will be10.25m, in Taiping it will be14.30m.Main findings:(1) According to the characteristic of groundwater system with many artesian wells and springs in the Leizhou Penisula, the MODFLOW program is modified based on the seepage-pipe flow model to simulate the ground water flow in the springs and artesian wells system.(2) the impaction and control function on the flow pattern of groundwater are revealed, the tracer migration numerical model is established and is used to calculate the groundwater circulation time in the volcanic area.(3) based on physical experiment, it is found that the real conductive coefficient in practice is lto2orders magnitude greater than that calculated from the ideal formula, this result is very helpful for determing the parameters in using seepage-pipe flow model to simulate artesian well, springs flow in aquifer systems.Sugestions:The determination of boundary condition is one of the difficulties in numerical simulation. When establishing the numerical model, the boundaries are assumed to be constant heads, equivalent to the sea surface elevation. In fact, only the first layer is completely consistent with the assumption. For the intermediate and deep aquifer, the boundaries in the sea are hard to be determined. In the flow modeling, equivalent boundaries are used, but noticeable defects will occur in solute transport model. For more accurate characterization of boundary conditions, more boundary data and specialized investigations are needed in further studies. |
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