Long-Throated Flumes and Broad-Crested Weirs

ISBN-13: 9789024731138 / Angielski / Twarda / 1984 / 142 str.

Marinus G. Bos; M. G. Bos

Opis

In the context of water management, structures that measure the flow rate in open channels are used for a variety of purposes: (i) In hydrology, they measure the discharge from catchments; (ii) In irrigation, they measure and control the distribution of water at canal bifurcations and at off-take structures; (iii) In sanitary engineering, they measure the flow from urban areas and industries into the drainage system; (iv) In both irrigation and drainage, they can control the upstream water at a desired level. This thesis represents an attempt to place such flow measurements on a solid foundation by explaining the theory of water flow through 'long-throated flumes' and their hydraulically related 'broad-crested weirs'. On the basis of this theory, and on practical experience, these structures are recommended for use whenever the water surface in the channel at the measuring site can remain free. The thesis concludes with a design procedure that will facilitate the application of these structures. The idea to undertake research on discharge measurement structures was born upon my appointment as the first civil engineer with the International Institute for Land Reclamation and Improvement (ILRI). Because my recruiter, Ir. J.M. van Staveren, then Director of ILRI, had left the Institute before my arrival, and because I was the 'first of my kind' in an agricultural environment, I looked for contact and found - vii- support from: the late Prof. Ir. J. Nugteren, Prof. Ir.

Spis treści

1 The Advantages of Using Broad-Crested Weirs and Long-Throated Flumes.- 1.1 Introduction.- 1.2 Advantages.- 2 History of Flumes.- 2.1 Introduction.- 2.2 Flumes with piezometer tap in the converging transition.- 2.3 Structures with head measurement upstream of the converging transition.- 2.3.1 Evolution of the structure until about 1940.- 2.3.2 Discharge rating based on boundary layer development.- 2.3.3 Discharge rating based on H1/L ratio.- 2.3.4 Estimate of the modular limit.- 3 The Head-Discharge Relationship.- 3.1 Basic equations.- 3.2 Specific energy.- 3.3 Head-discharge equations.- 3.3.1 General equation for ideal flow.- 3.3.2 Rectangular control section.- 3.3.3 Triangular control section.- 3.3.4 Truncated triangular control section.- 3.3.5 Trapezoidal control section.- 3.3.6 Parabolic control section.- 3.3.7 Circular control section.- 3.3.8 U-shaped control section.- 3.3.9 Truncated circular control section.- 3.3.10 Summary of equations.- 3.4. Equivalent shapes of control sections.- 3.5. Discharge coefficient, Cd.- 3.5.1 Physical meaning.- 3.5.2 Cd values.- 3.5.3 Influence of transition shapes on Cd.- 3.6 Approach velocity coefficient, Cv.- 3.6.1 Physical meaning.- 3.6.2 Cv values for various control shapes.- 3.6.3 Summary of Cv values.- 3.7 Alternative rating by iteration.- 3.7.1 Equations for ideal flow.- 3.7.2 The rating procedure.- 4 Required Head Loss Over the Structure.- 4.1 Introduction.- 4.2 Theory.- 4.2.1 Energy losses upstream of the control section.- 4.2.2 Friction losses downstream of the control section.- 4.2.3 Losses due to turbulence in the zone of deceleration.- 4.2.4 Total energy loss requirement.- 4.2.5 Procedure to estimate the modular limit.- 4.3 Hydraulic laboratory tests.- 4.3.1 Description of model tests.- 4.3.2 Measuring the modular limit.- 4.3.3 Head loss H1 — Hc.- 4.3.4 Energy losses downstream of the control section.- 4.4 Experimental verification of modular limit estimate with recent tests.- 4.5 Visual detection of modular limit.- 5 Demands Placed on a Structure in an Irrigation and Drainage System.- 5.1 Introduction.- 5.2 Function of the structure.- 5.2.1 Measurement of flow rate.- 5.2.2 Controlled regulation of flow rate.- 5.2.3 Upstream water level control.- 5.3 Head loss for modular flow.- 5.4 Range of discharges to be measured.- 5.5 Error in the measurement of flow.- 5.6 Restriction of backwater effect.- 5.7 Sediment transport capacity.- 5.7.1 Design rule.- 5.7.2 Laboratory experiments.- 5.8 Design procedure for a structure.- Summary.- Samenvatting.- List of Symbols.