Greywater Irrigation System | Cape Town IRT

Project Info

  • Category

    Greywater, Public Works

Greywater Irrigation System Works


Due to the location of the narrow  planted areas and the sandy soil drying out- a permanent greywater irrigation system is installed. In order to decrease the demand on drinking water, the City of Cape Town extended a main effluent line. Accordingly non potable, greywater is available to irrigate.  The result is a significant, 85-95% , decrease in potable water use.

However, the quality of water is variable and suspended particles, algae, and other organisms are present. In order to prevent clogging, there needs to be a high degree of filtration. This water quality significantly influenced, not only the irrigation material selected, but also the protocols set up for maintenance.

These suspended particles and organisms result in a need for larger emitters. Automatic, self-flushing filters provide primary filtration and are specified at all water take-off points. Additionally screen filtration, found at each sprinkler head,  catches any additional debris. The maintenance protocols require regular cleaning of filters and sprinkler nozzles.

This system is decoder based. There is also a rain sensor for each controller. Thus there is no irrigation during and after a rain event.

Irrigation Design |  Irrigation Consulting | Cape Town, South Africa

Solving Challenges


In short, the exposed, sandy and vast 19km long site presented a challenge. A conventional irrigation system uses extensive copper cable.  However, this would result in increased installation costs and secondly, vandals love copper. So, instead of using copper wires, the system is decoder based. This means far less cable is required. To further protect against the rife vandalism, valves are sunken into concrete valve boxes. Also, there are no standpipes on site. No drip irrigation is used due to local rats. (rats ate all the other drip in the area)

Simple maintenance is important. The greywater has variable water quality and requires a high degree of specialised filtration. Thus the self-flushing filter banks are fully automatic. Otherwise, the system would require a twice daily, manual clean.

Wind drift creates water waste. This results in decreased irrigation efficiency and a lower uniformity. Solving this challenge with a sprinkler system is not simple.  In this situation, the wind effect is decreased by using a small watering window.  Additionally, the system irrigates between 12 am and 6 am, when the wind is at its lightest. As an added benefit, the sprinkler system washes the accumulated salt off the plant foliage.

Project


The Cape Town Integrated Rapid Transit System an initiative that seeks to integrate all modes of transport into one coherent package for users. Part of the route incorporates bus stations, cycle tracks and footpaths.


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