Use of floodgates as flow measure structures in irrigation canals

The structures in the irrigation districts to control the flows and water levels, as well as water measuring, are fundamental to bring order to the distributing canals operation and the volumetric delivery to the irrigated areas. Water delivery is carried out at control points supervised by the districts, the limited responsibility societies, the irrigation modules and the users at a parcel level. At this point, measuring structures are of different types according to the topography and hydraulic, geometrical and operative characteristics in places where the structures are located. They can be windmills, velocity sensors of different types like fixed and portable, weir and floodgate type holes. The flows and levels in the canals are normally controlled through floodgates and weirs; although the structures use is not for measuring, an experimental relationship must be established to determine the flow from the water levels and gap. Flat, vertical and radial floodgates have been used as control and flow structures in the main canals of the watering districts in Mexico. Due to the importance of these structures in the canals operation, an analysis was carried out on the precision and trust of the water measuring with floodgates functioning at free discharge and drowned. As from the simplified equations for Saint-Venant transitory flux at the structures vicinity, functional relationships were established between the up-stream waters level, down-stream and gap, and were proven in different precision and confidence ranks to estimate the flow. The validness of these relationships was analyzed through experimental data of calibrated floodgates in the Enzo Levi laboratories at the Mexican Institute of Water Technology and the Irrigation Department at the Autonomous University of Chapingo. The existing differences between the experimental flows and the ones estimated through the structure calibration model confirm that the floodgates can help as flow structures as long as the functional relationships established are verified.