5. Calibration of Gates and Sluices

In many irrigation distribution systems, the flow of water is measured through gates and sluices. This measurement necessitates calibrating the gates and sluices.

In calibrating an individual gate, the discharge can be measured by any of the standard methods described in earlier chapters of this manual. A series of discharge measurements covering the range of openings is made, and the mean operating heads upstream and downstream from the gate are recorded for each measurement. For convenience when operating the gates in regular service, rating curves and tables may be compiled to provide the discharge in cubic feet per second (ft3/s) for each opening and series of operating heads.

In calibrating sluices that meet the requirements of rating sections, the current-meter method is commonly used. It may also be practical to calibrate the sluice with a temporary weir, provided sufficient fall is available. The calibration consists of measuring the discharge for various depths of flow in the sluice at a rating station and plotting the discharges against depths. The channel should be of regular section and free from disturbance caused by upstream conditions such as bends, multiple gates operating at unbalanced openings, waves, and other distorting influences.