Study On Karst Development Characteristics And Leakage Of Yu Donghe Reservoir

In the certain geological conditions, the water level of the reservoir which wasraised by the water accumulation may drive the reservoir to leak and lower the waterstorage capability through the underground passage like the adjacent areas or thedown-stream, as a result it may have an effect on the result of impoundment. Becauseof the karst development, especially karst conduit appearing, it is more likely that thereservoir gets severe and permanent seepage, what’s the osmotic quantity can’t beignored.The normal storage level of the YuDonghe reservoir was599m, the backwaterlength of the reservoir area was6km. The basin of the dam area and the reservoir areawas composed of the Triassic soluble rocks, the distribution is NW zonal. Amongthem, T₂l, T₁j, T₁f karst are more likely to be highly-developed bedding, the karst ismainly in the form of caverns、karstic pore and karstic cave, so it may cantain theunderground passage which result in serious leakage. From the terrain the northwestof the reservoir is a higher ground, the height of the cheuch is well above the nomalwater level. To the southeast, the height of the cheuch is590m at Lijiahe theformation boundaries in T₃x and T₂l, as well as there is a development of a large caveat the height of598m which is lower than the normal storage level of the YuDonghereservoir. The conditions of the underground passage and the hydro-dynamicconditions of leaking to the adjacent vale are existing. Therefore the karst leakageproblem of the reservoir and the dam becomes prominent.Based on the conditions of the environmental geology, the paper discussed thehydro geological conditions on the groundwater system of karst area, found out thedevelopment degree and scale of the surface and underground karst, summarized themain distributing rule of the soluble rocks, evaluated the results of the water pressuretest of rock mass in the study area. Base on the descriptions above, it analysed the suspected karstification path and the suspected pattern of the leakage. Adoptingthe hydrodynamic exacting method discussed the existence of the divide, using thesoftware of modflow to simulate, in order to predict the simulation of the divideexistence between the Yudonghe reservoir and the adjacent vale, the offset amplitudeof the watershed after the water accumulation, the quantity of the dam leakage indifferent working conditions, and then made the measures and suggestions aboutseepage prevention.The main research content and result are as follows:（1） This article has carried on the diagnosis to geographic and geomorphicconditions, formation lithology, geologic structures, regional techonic stability andKarst hydrogeology conditions.And also do research on the engineering geology andhydrology geology conditions.（2） Based on the analysis of karst scale, development and distribution, this articlehas done research on the mechanism and dissolution regularity of distribution.Andfocus on the underground karst medium corrosion situation and hydrological geologycharacteristics, giving clarification of the possibility of karst seepage channels.（3） This paper analyzes the penetration ability of the karst medium through thewater pressure test data, and summarizes the upward and vertical permeability ofspatial distribution characteristics of dissolvable rock in reservoir region, whichprovides the basis and hydrogeological parameters for the model that can begeneralized.（4） By means of analysising the condition of hydrodynamic force’s leakage fromproject area to adjacent valley, discussing the hydrodynamic force’s strength, usingthe interfluve hydrodynamics thoery, caculating the watershed’s altitude and location,to make the hydraulic connection between Yudong River and Lijia River clear.（5） This paper using Three-dimensional Numerical analysis method to simulatethe groundwater seepage field in cases of before and after impounding, seepagecontrolling. At the same time, confirm the existence of the watershed by calculation.Under the condition of the reservoir, the model calculates the leakage quantity of damfoundation and dam shoulder.The results is that leakage amount of dam foundation is1512.6m₃/d, the seepage quantity of left dam abutment is761m₃/d and the right damshoulder is492m₃/d. And then the total leakage amount is2765.2m₃/d. The mainleakage parts are the dam abutment and dam foundation. After combined withimpervious curtain, the total leakage of reservoir amount is1234.5m₃/d.,which is the2.26%of design capacity of the reservoir. The depth of the anti-seepage curtain is94m. （6） Due to the different simulation results of karst developmental characteristics,rock permeability propertiesand and reservoir seepage field, it is thought that thedegree of karst development is relatively low in the Yu Donghe reservoir.This paperputs forward reasonable seepage control measures and suggestions to ensure safeoperation of the engineering.