Long-Throated Flumes and Broad-Crested Weirs

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.