| Although the construction of urban lakes has the advantages of improving the quality of human settlements in urban areas,it will also profoundly change the regional water environment,especially the groundwater environment,which may eventually lead to a series of water resources,environmental geological problems.On the basis of summarizing the domestic and foreign research results and analyzing the hydrogeological conditions of the study area,this paper studies and discusses the leakage quantity and its influence on groundwater level and groundwater quality after construction of Kunming pool by means of data collection,field investigation,intelligent monitoring of hydrometeorology,monitoring of lake water level and groundwater level.The research results can provide technical reference for the construction management and anti-seepage design of Kunming pool,and also have important significance for protecting the groundwater environment in the area.Key results were achieved:(1)In 1986～2016,the groundwater level in the study area showed a trend of"flat-decreasing-increasing-slow-incremental increase",with a m.of 0.9～1.4m in the year During the early 1990s,the groundwater level of the Taiping Zhuang Nan and Dou Men Middle School monitoring stations,the closest to the Chihu District of Kunming,began to decline rapidly,gradually rising after 2003,with an average annual rise of 0.76m/a、0.81m/a,respectively.(2)Based on the data of engineering survey and core sampling,the vertical permeability coefficient of sediments in the north pool is 2.44～22.68cm/d,and the vertical permeability coefficient of sediments in the south pool is 3.47～15.91cm/d.The spatial variability of vertical permeability coefficient of sediment in lake area was analyzed by geostatistical method,and the optimal fitting model was determined.north pool Kv spherical model fits best and has moderate spatial correlation in the plane;south pool Kv gaussian model fits best and has strong spatial correlation in the plane.The sediment structure is the main reason for the spatial variation of permeability coefficient.the kriging interpolation partition is carried out based on the optimal fitting model.the area with 5～10cm/d in the north pool accounts for68.86%of the total area of the north pool;the area with 5～10cm/d in the south pool accounts for 55.29%of the total area of the south pool.(3)Through hydrometeorological monitoring,the leakage of test section of Kunming pool was calculated by water balance method 6196～7686m~3/d.The leakage at the bottom of the lake is 26 times as much as that in the lake area before Jianhu,which leads to the uplift of local groundwater level.Through the analysis of the monitoring results of the groundwater level and the lake water level around the lake in the test section,the near-shore groundwater level rises 0.74m,and the far-shore groundwater level rises 0.49m.for every 1m,in the test section.(4)A numerical model of the unsteady flow of diving in Kunming pool was established to simulate and predict the leakage and the change of groundwater level in Kunming pool after water storage under five scenarios:no seepage control,partial seepage control(loam replacement,geomembrane laying)and total seepage control(loam replacement,geomembrane laying).The stable annual leakage in each scenario is 16.836 million m~3,9.826million m~3,9.156 million m~3,2.936 million m~3,and 50 million m~3,respectively;and the corresponding leakage prevention situation is poor,medium,medium,good and very good.When there is no seepage control or local seepage control at the bottom of the lake,the water level of the lake area will be high,and soil salinization may occur.The flow field of groundwater in the lake area is basically unchanged when all seepage is prevented.(5)By comparing the groundwater level of Jianhu Lake with that of No Jianhu Lake,the influence of Kunming pool construction on groundwater level was analyzed.The results show that the groundwater level of the lake area rises under four scenarios:no seepage control,partial seepage control(loam replacement,geomembrane laying)and total seepage control(loam replacement),the maximum elevation is 8.5m,6.5m,6.0m,1.6m,and the obvious influence range(Higher than 0.5m)is 56.7km~2,37.0km~2,33.5km~2,10.4km~2.respectively When using geomembrane to prevent seepage at the bottom of Kunming Lake,the leakage amount is less than that of the lake area when the lake is not built,and the groundwater level of the lake area drops,the maximum drop is 1.4 m,the obvious influence range(Decline more than 0.5m)is 13.8km~2.(6)Based on the model of groundwater flow,a model of solute transport in groundwater was built,and the influence of water leakage on regional groundwater quality was analyzed.The results show that the source of groundwater pollution mainly comes from the lake water of Beichi,and the range of ammonia nitrogen exceeding the class III water standard of groundwater quality after 50 years of storage in Kunming pool is 18.18km~2,the influence range is 25.30km~2,and the maximum migration distance is 1016m.The over-standard range of COD in Kunming pool after 50 years of storage is 21.57km~2,the influence range is27.18km~2,and the maximum migration distance is 1266m.In general,the lake water leakage has little effect on the groundwater quality in the area. |
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