ABSTRACT
In general, the operation of a canal requires information about the circulating flow rates at various points. In free level canals, this is generally achieved through the use of special concrete works known as measurement structures, which make use of the hydraulic properties of weirs, with thin or thick crest as applicable, in order to establish the circulating flow rate in function of the water energy height upstream. It is only necessary to know the measurement structure characteristics, which will then provide the flow rate formula as a function of height. By entering this into the formula, we will be able to obtain the flow rate. In all weirs, the water flows over a wall that includes a notch, which
exactly delimits the width of the spilling water surface. There are three possible types of weirs. Some have thin crest (Figure 15.1)
and others thick ones (Figure 15.2) and within the latter type there are other special ones, such as the Creager and Ogee, etc., which possess the special feature of being the ones that discharge most. Thin crested weirs are commonly named “sharp crested weirs”. All weirs obey the following formula:
Q= c ·b ·h3/2
Where,
Q is the flow rate in m3/s c is a coefficient that depends on the weir type and characteristics b is the width of the weir notch in metres h is the water energy height above the weir crest, in metres.
