Deterministic Methods in Systems Hydrology - Chapter 2

Bản chất của hệ thống thủy văn2,1 chu kỳ thủy AS Một HỆ THỐNGChu kỳ thủy văn thường được miêu tả trong một hình thức tương tự như thể hiện trong hình 2.1 được lấy từ một tác phẩm tham chiếu cổ điển bởi Ackerman et al. (1955). Một đại diện thay thế, đó là phù hợp hơn cho các cuộc thảo luận hiện tại, được thể hiện trong hình 2.2. Trong hình này, các hình chữ nhật biểu thị các hình thức khác nhau của lưu trữ nước trong khí quyển, trên bề mặt của mặt đất, trong vùng...
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Deterministic Methods in Systems Hydrology - Chapter 2 CHAPTER 2 Nature of Hydrological Systems 2.1 THE HYDROLOGICAL CYCLE AS A SYSTEM The hydrological cycle is usually depicted in a form similar to that shown in Figure 2.1, which is taken from a classical reference work by Ackerman et al. (1955). An alternative representation, which is more suitable for the present discussion, is shown in Figure 2.2. In the latter figure the rectangles denote various forms of water storage: in the atmosphere, on the surface of the ground, in the unsaturated soil moisture zone, in the groundwater reservoir below the water table, or in the channel network draining the catchment. The arrows in the diagram denote the various hydrological processes responsible for the transfer of water from one form of storage to another. A study of Figure 2.2 reveals the relationship between the various forms of water storage and water movement. Thus the precipitable water ( W) in the atmosphere may beWater storage andwater movement transformed by precipitation (P) to water stored on the surface of the ground. In the reverse direction, water may be transferred from the surface of the bare ground or from vegetation to the atmosphere by the processes of evaporation and transpiration (E, T). Some of the water on the surface of the ground will infiltrate the soil through its surface (F) while some of it may find its way as overland flow (Q0) into the channel network. During and following precipitation, soil moisture in the unsaturated sub-surface zone is replenished by infiltration (F) through the surface. If the field moisture deficiency of the soil, due to evaporation, transpiration and drainage since the previous precipitation event, is substantially satisfied by the current event, there will be a recharge (R) to groundwater, and also a certain amount of interflow (Qi) or lateral flow through the soil, which is intercepted by the channel network. The groundwater storage is depleted by groundwater outflow (Qg), which enters the channel network and supplies the streamflow during dry periods. During prolonged drought, soil moisture may be replenished through capillary rise (C) from groundwater. Overland flow (Q0), inter-flow ( a) and groundwater flow ( Qg) are all combined and modified in the channel network to form the runoff (R0) from the catchment. These various hydrological processes are discussed in detail in textbooks and monographs on physical hydrology (e.g. Eagleson, 1969; Bras, 1990) and are dealt with here in subsequent chapters. It is not easy in practice to distinguish from a record of runoff, the separate components of overland flow, interflow and groundwater flow discussed above. In the case of experimental plots, or of short-term event investigations, techniques using chemical or radioactive tracers can he used. However, these methods are not suitable for long-term routine monitoring of large catchments. The most that can be done is to distinguish between the relatively rapidRapid response response of the catchment to a precipitation event and a second slower response. The quick response is often identified with surface runoff in the form of overland flow and interflow in the upper layers of the soil, and the slower response with the passage of the water through both the unsaturated and saturated soil moisture zones. Accordingly, most models of catchment behaviour used in applied hydrology are elaborations of the simplified catchment model shown in Figure 2.3. In this figure, the total response of the catchment to precipitation is due to three sub-systems: one representing direct storm response, the second representing - 24 - groundwater storage and outflow, and the third representing the unsaturated soil moisture zone. It would be desirable to model the overall catchment response shown in Figure 2.3 by aThreshold effect linear model. However, it is generally considered that recharge to groundwater ...