Research On The Karst Developing Characteristics And Seepage In Dam Area Of Charikou Hydropower Station

Charikou Hydropower Station is located at the downstream of Ziqu River in thesouthwest of Yushu county，which is belong to the secondary water system ofLancang river，at the dam site area mainly distributed Upper Triassic ligation groupcarbonate rocks and developed dissolved pore、dissolve gap and small karst caves.Reservoir seepage may happen along the karst passage after impoundment, which willaffect the normal functioning of reservoir efficiency, and may even threaten damsafety.In this paper, according to field geological survey and the early geologicalexploration data, discussed the karst developed morphology, size and spatialdistribution characteristics, and explored the karst development rule in dam site areabased on the geological environmental conditions of the dam site; analyzed thecorrelation of karst development characteristics and water permeability of rock massat the dam site；described the possible seepage ways and seepage passage in dam sitearea（dam seepage、seepage by-pass the dam），and estimated the seepage flow ofdifferent engineering parts by using the traditional hydrological geology method. Byusing the Visual MODFLOW software, established a three-dimensional numericalmodel of groundwater seepage in dam site area to forecast the seepage filed andseepage flow, meanwhile, put forward seepage prevention advice based on the size ofseepage flow at different depths of the impervious curtain.Main research results have the following aspects：1）Analysis of groundwater chemical characteristics and aqueous mediumpermeability of the dam site area show that: the groundwater chemistry type isHCO3-Ca and the surface water chemical type is HCO3-SO4-Ca. The subject rockmass are moderate to weakly permeable within the range of the exploration depth,the permeability of rock mass is relatively weak on the left bank, which weakpermeable rock is most developed, and the rock permeability is relatively strong in theriverbed and on the right bank, exists higher proportion of moderate permeability rock in addition to weak permeable rock.2) Karst development pattern, scale, controlling factors and the characteristics ofits development are controlled by lithology and structure; karst development is notuniformity; and it exhibit vertical zonation phenomenon in space,The optimaldistribution of elevation range of drilling karst is3850~3860m and3900~3930m.3) The seepage of each seepage passage is preliminary estimated by using theanalytical expression and the analysis of the hydrodynamic conditions and theseepage passage conditions of the dam site area, in which dam foundation is18365.3m3/d, by-pass the dam is6966.25m3/d, and the total amount of seepage is25331.55m3/d.4) In accordance with the three working conditions，natural conditions、Waterstorage conditions and impervious curtain，stimulate the seepage field by building athree-dimensional model of groundwater flow field of the dam site area and calculatethe seepage for some key position that may cause seepage. The model resultscan beperceived that the seepage decreased distinctly owing to the impervious curtain, butwhen the impervious curtain rose to80m the decrement is less.5) According to the simulation analysis of the result for the chemicalcharacteristics of the groundwater、permeability of the water bearing medium、characteristics of the karst development and seepage field of different workingcondition，the permeability of rock mass and the degree of karst development overallis weaker in the dam site area of Charikou hydropower station；it is less likely tooccur mass seepage， in order to the normal operation of the reservoir, seepagecontrol measures is still necessary to take in the main seepage site...