A SIMPLE METHOD FOR CALIBRATING A RADIAL GATE FOR USE AS A FLOW MEASURING DEVICE

A simple method for the calibration and use of an existing radial gate as flow measuring device under submerged flow conditions is presented. Details on equipment and calibration methodology are discussed including: determining required gate opening parameters and flow conditions for which the method is valid. Flow is calculated with a submerged orifice equation using a constant drainage coefficient. This methodology was applied to a radial gate located in the United Irrigation District in South Texas. The gate was instrumented and monitored continuously over a three-month period. Measured versus predicted flow varied by less than 4%. The method was compared to a more complex equation which accounts for submerged flow conditions and results in a mean absolute relative error of 3%. Analysis of individual flow events revealed significant hysteresis when estimating gate opening from an actuator position signal. This accounted for a difference in the calculated flow of up to 0.13 m(3) s(-1).