| Based on the mathematical analysis of potential theory, Hubbert protracted the schematic diagram of flow net in the interfluve which contained both ascending and descending streamlines in1940. This achievement opened the door to the theory of groundwater flow system (GWFS), which also broke up the tradition set of only horizontal motion in interfluves. In1963, the Canadian scholar Toth got three-order groundwater flow systems (local, intermediate and regional flow system) in the drainage basins with homogeneous isotropic medium under strict assumption of constant-head upper-boundary, and based on this study he proposed GWFS. In the past several decades, the GWFS theory was gradually improved by the efforts of Toth and Engelen etc. follow-up researchers both at home and abroad. However, limited by "Toth’s method", some defects of the GWFS theory still remain. In the meantime, the transformation regularity of groundwater flow patterns is seldomly analyzed based on Darcy’s law and the physical mechanism of groundwater flow patterns is not revealed completely. In order to work out these problems, we carried out the following works.(1) Through reviewing the GWFS theory and its evolution, the achievements of Hubbert’s and Toth’s study were discussed, flow net in the interfluves of Hubbert and multi-hierarchies of GWFS of Toth was represented by the simulation model of interfluves and GWFS, respectively. Then more applicable method for groundwater flow will be distilled by comparing the results of physical simulation, Hubbert’s study and Toth’s study.(2) Experiments of Groundwater flow patterns under changes of infiltration intensity are carried out by using simulation model of GWFS.(3) Based on the physical simulation experiments and numerical simulation of flux upper-boundary with single controlled factor, the transformation regularity of groundwater flow patterns are discussed.(4)Based on the numerical simulation and calculation, the hydraulic gradient coefficients of various groundwater flow patterns are obtained and the transformation regularity of groundwater flow patterns are discussed in the perspective of groundwater energy consumption rate.1. Simulated discharge areas are different under the condition of different upper boundariesPhysical simulation experiments in Lab can directly represent the flow net in the interfluves analyzed by Hubbert and multi-hierarchies of GWFS proposed by Toth. However, the upper boundary condition of both Lab model and Hubbert’s flow net in the interfluves are flux upper-boundaries, while that of Toth’s model is constant-head upper-boundary. The different boundaries result in different simulated discharge areas. The discharge area is the valley for both Lab model and Hubbert’s flow net in the interfluves, While in Toth’s model, the discharge area and the recharge area are of the equal area and symmetrical, the discharge area is not limited to the river valley.2. Simulation method of flux upper boundary is more suited to actual basin than that of constant-head upper-boundary①Groundwater table and groundwater flow patterns were controlled by topography in Toth’s model. However, through physical experiments, we concluded that topography controls groundwater table and groundwater flow patterns only in some condition. For the GWFS simulation of drainage basin, it’s impossible to control groundwater table, namely given constant-head upper-boundary in Toth’s model, and only to simulate infiltration intensity.②In Toth’s model, given the same constant-head upper-boundary, the recharge and discharge of the basin also change when changing other factors of the basin, such as permeability, length, depth and so on. This is not conducive to analyze how single factor influences the development of groundwater flow patterns. Simulation method of flux boundary can avoid these problem and is more suited to actual basin.3. Transformation regularity of groundwater flow patterns can be better recognized by using simulation method of flux upper boundary.Through summarize the results of physical simulation experiments and numerical simulation, we conclude that the groudwater flow systems will transform orderly with the changing of infiltration intensity, hydraulic conductivity, geometric configuration and number of possible sinks.①With increasing the infiltration intensity or reducing the hydraulic conductivity, groundwater flow patterns present similar changes, from simple regional systems to local-intermediate-regional systems, then to local-intermediate systems and finally simple local systems while other conditions keep constant.②With increasing the ratio of length to depth, the groundwater flow patterns present similar changes, from simple regional systems, to local-intermediate-regional systems, and then local-intermediate systems and finally simple local systems while other conditions keep constant.③While multiple sinks exist in the basin, sinks that affected the development of the groundwater flow patterns are ones that worked as real sinks, other ones only were possible potential sinks. The existence of multiple different sinks is a necessity for the development of multi-hierarchies of GWFS.4. hydraulic gradient characteristics of the transformation of groundwater flow patterns.Through changing each factors that affect the development of the groundwater flow patterns and calculating hydraulic gradient coefficient of different groundwater flow patterns, we concluded that new groundwater flow patterns develop by adjusting the hydraulic gradient coefficient with the change of each factor. Groundwater energy consumption rate is the minimum when regional systems develop, and it increases when intermediate or multiple local srstems develop.①Hydraulic gradient coefficient increases with the increase of infiltration intensity while other conditions keep constant, so groundwater energy consumption rate increases and local groundwater flow systems futher develop as the physical meaning of hydraulic gradient coefficient is the same with hydraulic gradient, and groundwater flow patterns present similar changes, from simple regional systems, then to local-regional systems and finally local-intermediate-regional systems with the increase of hydraulic gradient coefficient. In the meantime, whether infiltration intensity increases or hydraulic conductivity reduces, if hydraulic gradient coefficient is the same, the basin will develop the same groudwater flow patterns.②Sinks of the basin affect the groundwater flow patterns through ajusting the energy distribution of groundwater flow. Under the condition of the same infiltration intensity while other conditions keep constant, the more real sinks there are in the basin, the smaller hydraulic gradient coefficient and groundwater energy consumption rate is. While multiple potential sinks exist in the basin, groundwater flow patterns of smaller hydraulic gradient coefficient develop, Namely, groundwater flow patterns with lower energy consumption rate develop.③The ratio of length to depth of the basin affect the groundwater flow patterns through ajusting the energy distribution of groundwater flow. Under the condition of the same infiltration intensity while other conditions keep constant, if the same groundwater flow patterns develop, the bigger the ratio of length to depth of the basin is, the greater hydraulic gradient coefficient and groundwater energy consumption rate is. When groundwarer flow patterns transform, the bigger the ratio of length to depth of the basin is, the smaller hydraulic gradient coefficient and groundwater energy consumption rate is.The major innovations:Simulation method of flux upper boundary is determined. Based on transformation regularity of groundwater flow patterns, hydraulic gradient coefficient was introduced to analyze the physical mechanism of groundwater flow patterns in the perspective of groundwater energy consumption rate. This study is helpful to perfect the GWFS theory. |
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