Theewaterskloof dam has a capacity of 480 million cubic metres of water.
The catchment area of 500 square kilometres is served by streams emanating in the Hottentots Holland mountain range.
This area has a long-term average of 69 days with precipitation per year.
Historically records show we are in a dry period 1mm of rain per square meter equates to 500 000 000 litres falling on this area.
Hence it requires a full metre of rainfall with 100% runoff to fill the  dam from totally empty, which is unlikely to happen in any single year.
It takes a few days for all the runoff to reach the dam.
Evaporation and how saturated the ground is affects the amount of water reaching the dam.
An average amount of between 9% and 15% is used to offset the values against evaporation and soil absorption.
A deeper dam has less evaporation due to less surface area per volume.
Theewaterskloof dam has a capacity of 480 million cubic metres of water. The catchment area of 500 square kilometres is served by streams emanating in the Hottentots Holland mountain range. This area has a long-term average of 69 days with precipitation per year. Historically records show we are in a dry period 1mm of rain per square meter equates to 500 000 000 litres falling on this area. Hence it requires a full metre of rainfall with 100% runoff to fill the  dam from totally empty, which is unlikely to happen in any single year. It takes a few days for all the runoff to reach the dam. Evaporation and how saturated the ground is affects the amount of water reaching the dam. An average amount of between 9% and 15% is used to offset the values against evaporation and soil absorption. A deeper dam has less evaporation due to less surface area per volume.
Theewaterskloof Dam