Rivers, Water, Floods, Canals, Sand etc

Canal Water Administration System
The WAS (Water Administration System) is an integrated information management system for irrigation schemes that deliver water on demand through canal networks and rivers.

Their website is at https://www.wateradmin.co.za/ Click on "Irrigation Schemes" and select "Boegoeberg WUA" as example. You can for instance access the timetable from here to see when the canal will be standing for maintenance. This is usually 2 weeks at a time and about 6 times between March to July each year.

The canal also stands during the year over weekends every 4th week or so, for midge (muggie) control.
The Boegoeberg canal was started in 1926 and completed in 1933. It was cemented in the 1960's with a projected lifespan of 50 years. Boegoeberg is named for the small tree Croton gratissimus, also known as Bergboegoe.

During normal flow of water, very little sand is carried in the water, but the stronger the flow the sand contained in the water increases by the power of 6.

When the sand in the river contains 2 units of sand during normal flow, it will contain 2 to the power of 6 sand when the flow doubles. Thus the units of sand will not be 4, but will be 64 instead. 

The Boegoeberg canal has a mechanism to deal with sand during normal river flow, which is depicted in the image below.
The canal widens at the start of the canal. This slows down the water significantly and to such a degree that the sand and sediment filters down to the bottom. At the endpoint of this widening there is a wall in the way. The filtered "cleaner" water spills over the wall into the canal system. The sandy water that remains behind is guided via a separate canal back to the river.

During periods of floods this system cannot be used as the rate of water flow is simply too high,  hence the sand content in the water cannot be filtered effectively.

Select Boegoeberg link below to view all articles relating to this subject.