| In planning stage of hydropower project, it needs to investigate the related engineering geological condition and complete the geological demonstration of project planning. But, the environment is execrable and the traffic is inconvenient in the depopulated area of Tibet, the geological conditions are hard to survey, those finally cause the demonstration of project planning to suffer hindrance. So, it has high engineering values to establish a method of surveying the geological conditions and optimizing the hydropower station in those areas.Layue River, 2nd level branch of YalungTsangpo River, is located in the northwest of the great canyon region of YalungTsangpo River, more than half of basin is depopulated area. The average gradient of the mainstream of this river is 2.05%. The water catchment area is 2835km2 and the annual discharge of estuary for years is 96.5m3/s, therefore it has abundant hydraulic power. It has given 5 preliminary hydropower development plannings include Luomu River-Dongjiu River, Lamu River, Zhenluoma River, Layue River and LulangRiver, sum to 16 dams and 19 diversion lines, most of them are lower dams and longer diversion lines. The problems that meet in the process of engineering geological assessment of Layue River basin are as follows:(1) Because more than half of Layue River Basin is covered by primeval forest and natural reserve areas, routine means like exploration drilling and field survey are difficult to carry out;(2) Its traffic is very inconvenient because of high elevation of partially river reaches and sparsely populated;(3) Due to the complicated geological conditions and the large precipitation, geological disasters occurred frequently;(4) The environment is very bad; related materials are scarce in this region; the lush vegetation causes the bad intervisibility conditions and therefore remote sensing interpretation is difficult to implement and the result exists deviation;(5) Usually, the means of engineering geological assessment is qualitative assessment based on field survey, and its result often contains a lot of human factor. While the quantitative evaluation commonly is used with single engineering geological factor.Due to the existence of above problems, the geological demonstration of project planning is hard. So, we need to explore new methods that can be used in survey and evaluation on engineering geological conditions to achieve the goal of optimizing the hydropower station.First of all, we complete the remote sensing interpretation based on the relative datas that were collected before and correct its result after field survey. The process is simplified to “data analysis—remote sensing interpretation—field survey and verification—correction indoor”. We also summarize the characteristic of the engineering geological through analyzing the existing research results and counting the survey data. To be clear, we divide Layue River basin into 2 parts based on the field survey, namely region of detailed survey and region of reconnaissance, they are also divided into 5 parts and 6 parts respectively depend on the differences of engineering geological conditions. And also, the key influence range of dam site is defined as the 0.2km wide banding range which contains 1km long in front of dam and 0.5km long in back of dam; the key influence range of plant site is defined as the circular range whose radius is 0.5km; the key influence range of diversion line is defined as the banding range in 0.2 km width that is 0.1km away from itself. Then, establishing index systems and their grading standards separately on dam site, plant site and diversion line by qualitative evaluation which is completed considering the segmentations and project layout. And determining the relative importance of those indexes by the maximum correlation degreewhich is solved by the mean value of index in the key influence range. In the end, we calculate the weight of index using AHP whose judgement matrix is constructed depend on the relative importance of indexes determined before. In the region of detailed survey, for dam site and plant site, the index systems are the same, both include slope gradient, slope aspect, elevation, rainfall, the rock type, the influence of fault, the density of geological hazard, the density of gully, NDVI and topographic wetness index, sum to 10 indexes; for diversion line, the index system include the influence of fault, the rock type, the density of geological hazard, slope gradient and elevation, sum to 5 indexes. We also find that the influence of fault is the most important indexe for these three.We should deal with raster of each index first by ArcGIS to ensure those raster images have the same grid size, projection and extent. The superiority evaluation method of how to calculate the distance defined in extension theory, correlative degree, comprehensive correlative degree and priority-degree evaluating is finished by “Raster Calculator”. In this way, we get the results of priority-degree evaluating about the dam site, the plant site and the diversion line, and the number of grids in the key influence range represents the relatively good or bad. Considering the reality that it plans to use lower dam and longer diversion line in this basin, we decide that the weight of dam, plant and diversion line is 0.3, 0.45 and 0.25 in the same station. So far, we can order the stations and finish the model construction through weighted calculation on the number of grids. The result that only considers the conditions of engineering geological shows that the best dam sites are Baguo(high) and Baguo(low), the best plant sites are Layue, Dewu, Baimu, Zeba(long) and Dongfeng(long) and the best diversion lines are Dewu, Baguo(high), Baguo(low), Dongfeng(long) and Dongfeng(low). We also know the best station is Dongfeng(long) and the worst is Zhongguo.Finally, we integrate the assessment model and build an evaluation-sorting system using C# of Visual Studio 2008. The system which includes modules of data processing, model editing and evaluation is developed through component type, and it integrates the necessary tools provided by ArcGIS Engine developer kit which is contained in ArcGIS Desktop 10.0. It also constructs a database that we can operate to realize some functions such as add and delete data, update data, query data, statistics and order data automatically via sql. The system has been applied to sort stations in the region of reconnaissance and the result shows the density of geological hazards and the elevation are the most influential factors of dam site, and NDVI and slope influence the plant site more. For stations, considering the condition of engineering geological, Niubo and Bolang is the best, otherwise, Luomu and Gedongri is the worst. Comparing the result with the survey of field situation and qualitative assessment, it shows that the result of the evaluation system is relatively ideal. It illuminates that the model and the system constructed before can be used in those areas under the similiar conditions of engineering geological directly, or at least provides reference for others. |
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