| J. Toth got three-order groundwater flow systems (local, intermediate and regional flow system) in small drainage basins with homogeneous isotropic medium by analytical solution and based on this study he proposed the theory of groundwater flow system (GWFS). Then with the efforts of J. Toth and G. B. Engelen etc. follow-up researchers, concepts and methods of GWFS develop gradually. The system theory turns out to be a breakthrough for hydrogeology which brings various problems (groundwater flow field, water chemistry field and temperature field etc.) into a frame to study.As a new way and new trend of hydrogeology, many hydrogeologists utilize different methods to enrich and improve GWFS theory from different points. Yet the theory does not realize its merits completely in practice and the reasons are summarized as:there are defects in Toth's basin model and since the following researchers adopt the same propositions, it is hard to control the single influencing factor; the unclear function characteristics and rules of influential factors of groundwater flow pattern lead to insufficient understanding on order development characteristic and transformation rules of groundwater flow system; the physical mechanism of groundwater is not revealed completely.The main contents and method of this thesis as follows:(1) By collecting and analyzing previous research results, this thesis sums up the research status, development, future trends and deficiency of GWFS theory and groundwater numerical simulation.Through analyzing build method, computing results and GWFS order developing patterns of J. Toth's small drainage basin mathematical model, main influencing factors of basin GWFS control are discussed.(2) Based on small drainage basin model, using Visual MODFLOW to solve Toth's model, the thesis analyzes inefficiencies of the model in formation, transformation and controlling factors of groundwater flow patterns.(3) Basin groundwater flow model with flux upper-boundary is designed. The physical mechanism of GWFS is revealed by analyzing influencing and controlling factors of GWFS, pattern characteristics and transformation rules of groundwater flows, and making combinational analysis on different influencing and controlling factors.(4) Presenting basin groundwater flow characteristics through the analysis of GWFS speed field, distribution ways of low-velocity zones of basin water flow are discussed.We come to the following conclusion after above studies.1. GWFS development patterns of Toth's basin model are codetermined by total slope and partial slope of basin. In Toth's model, with tilt sine constant head condition, total slope of basin (standing for the whole gradient) determines intermediate and regional GWFS development and partial slope (indicating partial topographic relief caused by sine curve amplitude) determines local GWFS development. In Toth's model with level upper boundary in flow field, Groundwater flow pattern development and transformation rules are shown by numerical simulation.①When total slope is smaller than partial slope, simple local systems are presented.②When total slope is equal to partial slope, local-intermediate nested systems are presented.③When total slope is bigger than partial slope, local-intermediate-regional nested systems are presented.2. Changing flow field upper boundary into water table of Toth's model is more suitable to overcome defects of Toth's model.In Toth's model, with the same tilt sine curve constant head upper boundary, basin flux (including recharging and discharge) changes when basin depth or medium permeability is changed. Toth and following researchers study influences of basin size and changing permeability use constant head condition, but defects of the model make researchers hard to study influences and control effects of single factor to groundwater system development. Changing flow field upper boundary into water table of Toth's model is to make the model nearer to the truth and to increase precision of groundwater flow pattern description.3. Using flux upper boundary model and making infiltration intensity, hydraulic conductivity geometry (depth and length of basin) and potential sinks controlled independently, this thesis discusses influences of single factor change to groundwater flow pattern development and transformation.Changing a factor while keeping flux upper boundary constant, groundwater flow patterns change regularly.①With a reduction of infiltration intensity or increase of hydraulic conductivity, groundwater flow patterns present similar changes, from simple local systems to local-intermediate nested systems(two real sinks), and then to local-intermediate-regional nested systems (three real sinks), and finally simple regional systems (one real sink only) while other conditions keep constant.②With an increase of basin depth or reduction of basin length, groundwater flow patterns present similar changes, from simple local systems to local-intermediate nested systems(two real sinks), and then to local-intermediate-regional nested systems (three real sinks) while other conditions keep constant.4. Laws of influential factors effects of flux upper boundary basin correspond reversely. After comparative analysis and defining Ric and Rid, we can understand physical mechanism of GWFS.Comparing and analyzing the numerical simulation results by changing infiltration intensityε, hydraulic conductivity K, depth d and length L of flux upper boundary basin respectively, we draw the following conclusions.①With a reduction of infiltration intensity or increase of hydraulic conductivity, groundwater flow patterns present similar changes while other conditions keep constant. Defining the ration of infiltration intensity to hydraulic conductivity as Ric, the ratio Ric may be considered as the rate of driven force for groundwater flow due to the same value and dimension with the average hydraulic gradient and is a key factor to groundwater flow pattern development. Characteristics of groundwater flow patterns are same as long as Ric is same, though infiltration intensity or hydraulic conductivity is changed while other conditions keep constant.②With an increase of basin depth or reduction of basin length, groundwater flow patterns present similar changes, defining the ratio of depth and length as Rld. Same Rld results same pattern of groundwater flow while other conditions keep constant.③Potential sinks S is a necessity for GWFS development. When Different potential sinks exist, multi-order groundwater flow patterns may be developed under other conditions' effects.④With the interactions and coactions of various influential factors of groundwater flow patterns, groundwater flow pattern characteristics are self-organized and the process promotes optimizations of groundwater flowsAiming at the limitation of Tothian modeling method, this study puts forward the modeling method using upper flux-boundary and discusses two-dimension groundwater flow patterns and transformation rules. After defining Rlc and Rid, the thesis examines influential factors which correspond reversely and their physical mechanism. It is not only a major innovation of this study, but also a perfection of groundwater flow system theory.
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