The Research On Fissure Water System In The Dagang Mt. Reaches Of Dadu River Valley

The alpine valleys make up the main landform in the areas of southwestern and northwestern China, due to the rapid uplift of the QXP. Under the effect of long-term geological process, which includes regional tectonics, unloading effect, weathering, etc, the alpine valley develops many fractured media in rock mass. The fracture media mainly consists of joint, fault, dislocating fault, unloading fracture, weathering fissure, etc. The groundwater in the hard rocks stores in the fissures and faults, the amount of water is controlled by supply and development of the faults and fissur es. Fractured rock is highly anisotropic and heterogeneous which results in discontinuity of fissure water.The alpine valleys can also work as discharge area of regional groundwater flow systems and local slope groundwater flow systems. For interactions of multi-echelon groundwater system, fracture water is a special kind of complex type that contains diversity hydrodynamic and hydrogeochemical condition. In this paper, we mainly study the characteristics of fracture groundwater system in the Dagang Mt. reaches of Dadu River. The fracture water system, as a relatively special groundwater, is characteristic of multiformity and complexity with hydrochemical ingredients features, the abnormality on temperature and particular pressure-water factors in river bedrock. The study on fracture water system of the alpine valleys in the Dagang Mt. reaches of Dadu River is of great significance to basic research of confined fractured aquifer system and medium-low temperature geothermal water.The large-scale hydropower projects are most likely in alpine valleys, a condition caused by fracture water n special hydrogeological cases is inescapable. And confined fracture water system is the most significant.However, fewer works has been done on the confined fracture water system.The author has launched the research initiative to study the fracture water system in alpine valley's bedrock based on the geological data from the stage of the Dagang Mt. hydropower engineering survey and construction. The overall objective of this study was to understand the genesis of the confined fractured water system. Mainly through three channels to accomplish. That is fractured aquifer system, hydrogeochemistry, the dynamic variational characteristic of fracture water; following main conclusions are obtained:(1) The key insight uncovered by the study of the hydrogeological structure is this: the hydrogeological structure are controlled by the combination of the steep-dip vein fissured aquifer system of fault or dike zone and the gentle-dip densely fissured aquifer system. In order to study the rule of seepage flow in fissured rocks, the influence of permeability of fissures in different intersection angles and direction is compared. By comparison of the permeability of calculated value with the results of water pressure test, every model can fit for real data in there validity conditions. The hydraulic conductivity and anisotropy factor(K1/K3) decreased with increasing bedrock depth at the logarithmic rule. The vein fissured aquifer system exacerbated the heterogeneity and anisotropy in bedrock.(2) It is to divide the fracture water system into the deep confined fracture water sub-system and the shallow fracture water sub-system according to the hydrogeochemical characteristic. During the research, methods such as cluster analysis, the PCA method, the gray relational analysis, and the indication of stable isotopic are employed. The results show that, hydrochemical chara cteristics of confined fracture water indicate that paleo-fluid in reservoirs has the characteristics in sealed underground water but present underground water mixed with shallow fracture water, and the shallow fracture water showed a greater oxidation and dissolution. The replenishment source of the confined fracture water were similar to the hot springs in the adjacent region. Both can be all derived from the precipitation in the Gongga Mountain region.(3) These two kind of fracture water are different in the genetic mechanism and characteristic of groundwater regime. The shallow fracture water regime varied with the seasons, and divided into rise in status very soon, fluctuation in high water level and slightly drop, that is caused by local slope precipitation. The deep confined fracture water regime reflect the characteristic of the fracture medium stress-strain. The flow rate of autoflowing drill holes varied with seasons, including elastic release period and stability of autoflowing period. The autoflowing drills sensitive response to recharge of precipitation, what apply to drills of D3 and D201, but exclude D2 and D46. The anomalous earthquake signal and tidal effect of the water level of the drill D211 was more obvious.(4) The slope hydrogeological structure contributed to high level of hydraulic head in slope, and have definite control action of fissure water, but the level of fissure water affected by drainage datum plane is just as low as Dadu River in shallow weathered zone. It is to describe the temperature distribution of fracture water and then locate hydrogeothermal anomaly zones by means of bore temperature logging and evaluating reservoir performance. It follows that the characters of the geothermal anomaly concern many factors such as discharge of regional groundwater flow system, shallow fracture water flow system and slope hydrogeological structure. The confined fracture water is caused by combinations of regional groundwater flow system and local fracture water flow system, and local fracture water has dominated the mixed groundwater with more than a 90% share. The depth and temperature of confined fracture water is significantly linear correlated with the water pressure in cracks, but not with the level of onfined fracture water. Finally, this paper gets the conclusion to develop hydrogeologic conceptual model of low-medium geothermal and confined fracture water in granite bedrock in the Dagang Mt. valley based on the above research findings. The valley hydrogeological structure play an important role in controlling the effect mechanism of confined fracture water, which is combination of gently dipping fissure and steep-dip vein fissure.