Floodgates use delimitation as spillway structures in irrigation channels.

The control of flow, water level as well as water measuring in the channels of the irrigation districts are fundamental to put order in distribution and volume delivery in irrigation areas. The flows and water level in the channels are usually controlled with floodgates and spillways. Although the function of these structures is not of measuring, experimental relations have to be established to estimate the flow as from water level and the opening of the floodgates or the height of the spillways' crest. Due to the floodgates importance in the channels operation, an analysis was carried out about precision and reliability on water measuring in floodgates operating at free and drowned discharge, As from the simplifications of Saint-Venant's transitory flux equations in the vicinity of the floodgates, functions were established to relate the variations of the flow and water level immediately up stream and down stream of the structure. As well as the water level and the opening for critic and super-critic flow values down stream of the flood gate. These functions were tested for different precision and reliability ranges in estimating the flow through the floodgates, The existing differences between experimental flows and the ones estimated through the calibration model of the structures, confirm that the floodgates can work as spillway structures as long as the defined functional relations are verified.