DISCHARGE CHARACTERISTICS OF OVERSHOT GATES

Authors: Wahlin, Brian; Replogle, John

Submitted to: International Conference on Water Resources Engineering Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/22/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Increasing farm efficiency and maximizing crop yields require that the irrigation canals be effectively managed and controlled. Usually, water level control and flow measurement are accomplished by two separate devices. Researchers at the U. S. Water Conservation Laboratory have developed a single, practical, device that will do both. The device, an overshot gate, is sometimes called a leaf gate because it is simply a sheet of metal attached to the bottom of the canal with hinges that allow it to be raised or lowered in a manner similar to turning a page, or leaf, in a book. The water level is controlled by raising or lowering the gate itself, and through laboratory tests, equations were developed to predict the discharge of the gate and thus provide a means to measure the flow rate. With these results, canal operators are now able to use an overshot gate not only to control the flow, but also to measure it. Beneficiaries of this work include irrigation water projects and the farmers they serve.

Technical Abstract: Overshot gates are becoming increasingly popular for controlling water levels in open channels because they are able to handle flow surges with limited depth changes. While water level control is useful, operators also need to know the flow rate at each gate in order to operate the system better. Empirical equations were developed from laboratory testing to predict the discharge over leaf gates. These equations can accurately determine the flow rate in the field of a properly ventilated free-flow overshot gate to within 6%. These equations are valid for values of measured head-to-weir height ratios less than 1.0 and for gate angles between 16 and 63 degrees spanning the typical operating range. Additional equations can be used to predict the discharge of a submerged overshot gate; however, the degree of accuracy was not clearly defined.