5.12. FLOW MEASUREMENT The importance of accurate flow measurement for proper regulation, distribution, and charging of irrigation water cannot be overemphasised. There are several flow measuring devices available for flow measurement in irrigation systems. Generally weirs and flumes are used for this purpose. Besides, there are some other indirect methods by which velocities are measured and the discharge computed. In these methods, the channel section is divided into a suitable number of compartments and the mean velocity of flow for each of these compartments is measured by using devices such as current meter, surface floats, double floats, velocity rods, and so on. The discharge through any compartment is obtained by multiplying the mean velocity of flow with the area of cross-section of the compartment. The sum of all compartmental discharges gives the channel discharge.
