The streams that rise in Ekurhuleni and together become the Modderfontein River show large surges of water over a 24 hours cycle. These are the Kelvin Stream and the Sebenza Stream. The most striking pattern of flow is a lowest point about midnight followed by a surge in the early hours of the morning. This change can take place within a few minutes. Further changes occur but are less consistent and less marked.
The abruptness of the surges points to an active discharge of water. Whether this is waste water or reticulated water, the discharges must surely be dysfunctional.
The map shows the location of the sites. A time-lapse camera monitored the streams for periods from 24 to 96 hours, and the date and time stamp is on each photo. This report describes the changes in the Kelvin Stream, the Sebenza Stream, and the upper Modderfontein River.
A visual impression can be seen as a speeded-up time-lapse video.
Kelvin Stream at Dunbar Rd *
In the 48 hour monitoring period starting mid-afternoon flow surged at 18:00, then receded to a minimum at 20:30. There was a sudden surge at 03:30 reaching maximum in 20 minutes, illustrated in Figures 1 and 2. The following day flow remained relatively high with a surge at 18:00 and decline similar to the first day. A surge at 06:00 reached the highest level in the 48 hour period, and at 07:15 it declined to the lowest level at 12:15 when there was a new surge (Figures 3 and 4).
Sebenza Stream at Driefontein Rd, Isandovale *
The site is about 100 m downstream from Driefontein Road. The photos (Figures 5-7) show a dry channel at 01:05 which filled with water at 1:31 and reaching its highest point at 04:03. The grass in the foreground floated upwards to partly obscure the view before. The last photo shows the scene in daylight with a dry channel.
Modderfontein Stream at Crawford Rd, Illiondale *
This site is about 100 m upstream from Crawford Rd. Over a period of 96 hours a daily cycle emerged. Starting mid-day the flow is low and late afternoon it increases. From early evening it declines to a lowest level about midnight. At a point somewhere between 01:00 and 04:00 it rises suddenly and very rapidly to its highest level of the cycle. From about 08:00 it declines, sometimes to another minimum around mid-day.
The following photos show a typical mid-day low (Figure 8), end of day increase (Figure 9), mid-night low (Figure 10), early morning peak (Figure 11), and still high at sunrise (Figure 12).