Deterministic Methods in Systems Hydrology - Chapter 5

Mô hình tuyến tính khái niệm của Dòng chảy trực tiếpUngauged lưu vực5,1 HYDROGRAPHS UNIT tổng hợp Trong chương 4 chúng ta đã thảo luận phân tích hộp đen của hệ thống tuyến tính bất biến thời gian với tham chiếu cụ thể cho các thành phần của hệ thống phản ứng có liên quan với các phản ứng cơn bão trực tiếp đến lượng mưa. Thành phần đặc biệt này được minh họa trong hình 2.3 (giản thể lưu vực mô hình) là thành phần của phản ứng tổng lưu vực chuyển đổi Pe mưa hiệu quả cơn bão...
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Deterministic Methods in Systems Hydrology - Chapter 5 CHAPTER 5 Linear Conceptual Models of Direct RunoffUngauged 5.1 SYNTHETIC UNIT HYDROGRAPHScatchments In Chapter 4 we discussed the black-box analysis of linear time-invariant systems with particular reference to the component of the system response concerned with the direct storm response to precipitation. This particular component is illustrated in Figure 2.3 (Simplified catchment model) as the component of the total catchment response which converts effective precipitation Pe to storm runoff Qs. It was mentioned in Section 1.1 and again in relation to Figure 2.4 (Models of hydrological processes) that the black-box approach was one of the three general approaches to the prediction of the system output. In the present chapter we are concerned with the approach to the prediction of direct storm response based on simple conceptual models i.e. with an approach which is intermediate between the black-box approach discussed in Chapter 4 and the approach based on the equations of mathematical physics as applied to hydrological phenomena. Conceptual models It was noted in Chapters 1 and 2 that the term conceptual model can be used broadly to cover both black-box models based on systems analysis and mathematical models based on continuum mechanics. In this book, however, the term conceptual model will be used in the restricted sense of models that are formulated on the basis of a simple arrangement of a relatively small number of elements, each of which is itself a simple representation of a physical relationship. The most widely used conceptual elements of the direct storm runoff component are linear channels and linear reservoirs. These elements represent a separation and a concentration of the two distinct processes of translation and attenuation, which are combined together in the case of unsteady flow over a surface or in an open channel ( Dooge, 1959). The conceptual model of a cascade of equal linear reservoirs, each with a lateral inflow, corresponds to the assumption that the system function of black-box analysis may be approximated by the ratio of two polynomials (i.e. by a rational function). Such a conceptual model is, therefore, closely related to the black-boxRational function approach. On the other hand, the conceptual model based on of the St. Venant equations for the case of a vanishingly small Froude number. It may be said to represent a transition between a conceptual model of the direct storm response as a lumped system and a simplified distributed mathematical model based on the equations for unsteady free-surface flow. Conceptual models of direct storm response first emerged in hydrology in connection with the problem of synthetic unit hydrographs. It is a commonplace of applied hydrology that the important problems seem to arise in relation to catchment areas for which little or no information is available. Accordingly, it is not sufficient to be able to derive a unit hydrograph for a catchment area, in which there are records of rainfall and runoff, using one of the methods discussed in Chapter 4. It is also desirable to develop procedures - 76 - for the derivation of synthetic unit hydro-graphs and hence the prediction of storm runoff for ungauged catchments. This can be attempted, if rainfall and runoff data are available for similar catchments in the same general region. The basic approach used is as follows: (1) derive the unit hydrographs for the catchments in the region for which records are available; (2) find a correlation between some defined parameters of these unit hydrographs and the catchment characteristics: (3) use this correlation to predict the parameters of the unit hydrograph for catchments, which have no records of streamflow but for which the catchment characteristics can be derived from topographical maps. Sherman (1932a) published the basic paper on the unit hydrograph approach in 1932. In the same year he published a second paper, which was concerned with the relationship between the parameters of the unit hydrographs were in fact derived more t unit hydrographs were in fact derived more than ten years before the concept of the unit hydrograph itself appeared in print. In 1921 Hawker and Ross modified the classical rational method (Mulvany, 1850) to include the effect of non-uniform rainfall distribution by the use of time-area- concentration curves. These curves were estimated on the basis of the time of travel from various parts of the catchment to the outlet, as computed by hydraulic equatio ...