FLOW GAUGING

	General The first gauging weirs designed specifically to measure flow in South Africa were completed in 1904 in the old Transvaal Province. Almost without exception all the gauging weirs built in South Africa until the mid 70's were compound sharp crested structures. The first compound Crump weir was built in the Great Fish River in October 1977. Today flow is measured at more than 800 river flow gauging stations and at more than 200 dams. More than 55% of these stations include components at which flows are gauged with compound sharp crested weirs and more than 25% are gauged with compound Crump weirs. Methods such as velocity measurements, backwater calculations and slope-area are used to calibrate these stations for high flows. There are also a number of natural river sections calibrated specifically to measure floods. The Thumbnail images show examples of typical South African gauging weirs and equipment.   (click on the Thumbnail for larger image) Flume A sluicing flume was recently developed by Hydrology in co-operation with the WRC and University of Stellenbosch. The flume was developed to measure flow in sediment laden South African rivers. Measuring equipment The first mechanical water level recorder was installed in 1900 on the Vaal River near Vereeniging. The oldest operational gauging station equipped with a mechanical recorder is on the Pienaars River near Pretoria (A2H006), where recording started on 1 March 1905. Mechanical recorders are still in use to a large extent, but are being phased out or complemented by electronic devices. Since 1988, 73% of river flow gauging stations have been equipped with electronic equipment. This has not only lessened the burden of data editing and storage, but has paved the way for the collection of data in real time.		Crump weir Crump weir   Sharp crest Sharp crest Flume Boat measure Recorder hut