Oudtshoorn, 20 December 2022 – Earlier this week, 31 mm of rain was measured at the Raubenheimerdam. This was for the period between Monday, 12 December and 20 December 2022. The rain measured on the 12th of December 2022 was 12mm and for the 16th and 17th of December, it was 19mm. The dam level increased by 10cm this week and is currently at 69.37%.
It may seem like a very small rise in dam level after the week’s good rainfall, however, several factors need to be taken into account when considering the level of the dam:
- Not all of the rainfall will produce run-off. None of the rivers in the catchment area was flowing due to the drought and a large percentage of the rainfall never reached the dam because waterholes and pools in the dry river beds had to fill up first. The dry soil also needed to be saturated for more run-off to occur.
- The catchment area of the Raubemheimer dam stretches over 60 square kilometres and rain does not always fall over the entire catchment area. The rainfall figures given above were measured at the dam itself.
- When the Raubenheimer Dam was built in the 1970’s one of the conditions and agreements with farmers downstream of the dam was that the first water from the Boesman’s River would be diverted by means of a concrete canal around the dam and be released back into the river below the dam for the use of farmers along the river below the dam. This condition is still in force which means that the flow in the Bushman’s River has to be substantial before it feeds the dam.
- In hot weather, evaporation is also a key element. The annual evaporation level in the Klein Karoo is 2 metres per year which means that should the dam receive no water and no water is used, the dam level will drop by 2 metres a year. This means that about 17% of the volume of water in the Raubenheimer Dam is lost to evaporation per year. In summer the level of the dam could drop by 1cm each day implying that the 10cm rise in the dam level last week can be lost by evaporation alone in 10 days.
When it rains, the town does not stop using water. At present, with the high consumption and evaporation, and with no inflow, the level will drop by approximately 2% each week.
Any member of the public who is interested in the statistics and the practical side of our town’s water supply and wishes to have an informed view is more than welcome to contact the Technical Department of the Municipality where officials will gladly share information and explain how the whole water supply system operates.