Overshot Gates
There are a variety of solar-powered overshot retrofits which can be installed in a canal automation system. They include the: (1) draw-bridge gate; (2) pneumatic gate; and (3) scissor gate.
Drawbridge Gates
This overshot gate consists of a gate leaf, hinge, and hoist mechanism. One manufacturer is ARMTEC (www.big-o.com), a Canadian firm. This gate can be likened to a drawbridge hinged across the bottom of a vertical walled channel. When the gate is horizontal (fully open), water flows through the channel uninterrupted. As the cable hoist raises the downstream end of the gate, water flows over the lip while the channel sides restrict it. The hoist can be operated by a 12- or 24-VDC motor. Reclamation was involved in the successful installation of a ARMTEC gate in western Idaho (USA).
Pneumatic Crest Gate
Working with Obermeyer, Inc., in Ft. Collins, Colorado, USA (www.obermeyerhydro.com), overshot gates for use in check and similar structures have been tested. The Obermeyer gate is hinged across the bottom and moved up and down by an air bladder. A small 12-VDC air compressor is used to inflate the bladder. In 1994, an Obermeyer gate water was retrofitted into a check structure of a canal in north central Utah [3]. The next year a larger gate was installed at the Bear River Migratory Bird Refuge in northern Utah.
Scissor Gate
One version of the scissor gate, invented by Peter Langemann, was patented by the St. Mary Irrigation District, Lethbridge, Alberta, Canada, and is manufactured and marketed by Aqua Systems 2000 Inc. (www.aquasystems2000.com). The gate is an arrangement of hinged leaves that function as an adjustable weir to provide either flow control or instream level control. Each gate is fully self-contained and incorporates a 12-VDC motor and gear reducer, limit switches, electrical control panel, and solar power supply. Reclamation was involved with successful installation of the Langemann gates on three separate irrigation systems in southern Idaho (see Fig 7).
Figure 7. This solar-powered Langemann scissor gate regulates the flows out of a small water storage pond near Twin Falls, Idaho, USA.