Dòng chảy bề mặt môi trường phát triển trực tiếp dòng chảy, dòng chảy trong sông suối, chuyển giao hồ nước sông cửa hàng, lưu thông trong các hồ và ao hồ, dòng chảy ở các cửa sông, và cung cấp nước ngầm vào sông suối. Ống nhân tạo được xây dựng để vận chuyển nước mặt là phổ biến trong nước và quản lý nước thải, bao gồm các kênh mương, hệ thống thủy lợi, và hệ thống thoát nước. Trọng tâm của chương này là xem xét lại các yếu tố của dòng chảy bề mặt miễn phí. | 7 Surface Water Flows INTRODUCTION Environmental surface water flows develop as direct runoff flow in streams and rivers transfer of lake water to outlet rivers circulation in lakes and ponds flow in estuaries and groundwater supply into streams and rivers. Artificial conduits constructed to transport surface water are common in water and wastewater management including canals irrigation systems and sewer systems. The focus of the present chapter is on a review of elements of free surface flow in open channels under steady-state and quasi-steady-state conditions. Circulation in lakes and reservoirs is introduced briefly in Sec. though these flows are generally much more complicated and not amenable to the types of analyses typical of open channel flow. HYDRAULIC CHARACTERISTICS OF OPEN CHANNEL FLOW Basic Geometric Parameters of the Channel Cross Section A defining characteristic of open channel flow is the presence of a free surface open to the atmosphere and at which the pressure is zero or equal to atmospheric pressure in absolute pressure terms . As an example Fig. illustrates two types of common channels a a channel with trapezoidal cross section and b a channel with circular cross section. Much of the discussion that follows concerns basic parameters of channel flow in a trapezoidal channel since this is the most common shape used for constructed channels and also provides a reasonable approximation for natural streams. The cross-sectional area A of the channel is the area of the channel cross section measured perpendicular to the flow velocity vector. In the case Copyright 2001 by Marcel Dekker Inc. All Rights Reserved. Figure Parameters of the channel cross section a trapezoidal cross section and b circular cross section. of the trapezoidal cross section shown in Fig. A b my y by my2 where y is the depth b is the base width of the trapezoid and m is the side slope. Triangular and rectangular cross sections are particular .
