Rainfall and Jukskei River Catchment Information

Rainfall features Witwatersrand and Edenvale area *

There are some important features of rainfall in the Edenvale and upper Jukskei River catchment, which lies in a summer rainfall region:

• Rainfall is higher on the Witwatersrand Ridge than the surrounding area
• Rainfall is usually higher over a city, but the relationship can be more complicated
• Highveld rainfall follows an 11 year cycle of wetter and drier periods

Rainfall at six sites local from 1971/72 to 2015/16 roughly follows the 11 year pattern (first graph below). This places us now at the end of a dry phase, and peak of the next wet phase will be around 2020.

The first  figure below shows the positions of the six rainfall sites in relation to the Witwatersrand ridge, looking north. The graph that follows shows the average seasonal rainfall for the 23 year period from 1991/92  to 2013/14 that are common to five sites. Rainfall declines as one moves west to east. This could be due to the influence of the city to the west, or the ridge since the there are two ridges to the west and they are higher.  Compared to Kensington which is on the ridge, rainfall is 8% lower in Glendower and 19% lower in Edenglen. The five sites are in approximate order of distance from the ridge. 

Rainfall Edenglen *

The table shows Edenglen rainfall by month, year and season from 1983 to the 2016. The graphs show season to date rainfall for the last two seasons and the current season. The 2015/16 season started dry and the second half season was wetter, but at season as a whole was well below average. Unfortunately this distribution does not suit agriculture and it was seen a a drought year. The 2016/17 season started exceptionally wet and the second half season was also above average. Rainfall in the current season starting July 2017 is above average as at the end of December

Jukskei River Peak Flow Trend *

The Department of Water and Sanitation maintains hydrological stations on major rivers that measure the volumes and levels of flow. There is only one station on the Jukskei that is still functioning and that is Nietgedacht A2H023. This station has continuous monthly peak flows and levels for 50 years. The trend is to higher peak flows (see below). Statistical modelling of the data shows the peak flows have risen 10-fold over 50 years andwill increase 30% in the five years to 2020. This is roughly when the next wet phase will peak.

Acknowledgements *

Those who provided rainfall data are Alan Clark – Kensington, Costa Polous -Glendower, Irwin Juckes – Edenglen, Judi Dragan – Isandovale and Robert Rotteveel – Buurendal