Clandale: putting excess rainwater to good use

By Ilana Koegelenberg

A 25 000ℓ rainwater harvesting system was installed at Clandale Projects to brilliantly serve as a stormwater buffering system in case of flooding, while also providing backup water in case of water cuts.

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The problem

After the heavy storms and subsequent flooding in the Meadowdale, Johannesburg area last year, the client at Clandale Projects called in Burgess and Partners Plumbing Services to come up with a solution to prevent future water issues.

With the heavy rains last year, the infrastructure in the area was unable to cope with the excess rainwater from the continuous rainfall at the time. The Clandale property has stormwater facilities, as well as stormwater pumps that pump the rainwater into the municipal stormwater drains; however, the infrastructure in the area cannot cope with that amount of water.

They needed an alternative solution.

The solution

Warren Burger, business development manager at Burgess and Partners, got involved and suggested that a rainwater harvesting system take care of the excess water (which could then be used at the client’s will) and also provide a backup to the municipal water supply feeding the toilets.

The rainwater harvesting system would feed the 6 500m2 property’s irrigation system alongside the toilets, drastically reducing Clandale’s municipal water usage.

The client was happy with this solution and Burger got to work designing the system. He was also responsible for managing the installation with the help of two of Burgess’ trusted plumbers, Roland Palm and Sam Ngoepe, who completed the job in record time.

The system collects rainwater from a portion of the property’s roof and discharges into the five 5 000ℓ Rain Cell rainwater storage tanks. Depending on the client’s preference, the rainwater can then be used at will. By opening and closing two different valves, the system will automatically switch over from the municipal supply, after which the pump will engage and ultimately feed the building with pressurised backup rainwater.

The client can now let the water run out into the municipal stormwater drain at their own pace, allowing it to drain properly without flooding the entire system.

Tackling the project

Burger did a lot of research before sitting down to do the design. Preparations for the project involved working out the total roof space and calculating the rainfall quantities over the past 20 years.

He also had to calculate the best place to install the tanks. It was important to ensure that the tanks did not obstruct any windows and that they were not too close to any air conditioners. With regard to the pumps, it was vital to keep them isolated and away from gas bottles and other electronics, according to industry standards and requirements.


With the heavy rains last year, the infrastructure in the area was unable to cope with the excess water from the continuous rainfall at the time.


Burger went to site to establish the number of people on the property, together with the number of taps and toilets the system would be feeding. It was also important to find out what type of toilets were on site (flush master operated toilets or normal low level flushing toilets).

The system

The first phase of the project involved installing new 110mm PVC downpipes and five 5 000ℓ rainwater tanks to capture the rainwater off the main office block’s roof and a portion of the factory roof. Due to the design of the building, using 160mm pipework to discharge the rainwater would not have been possible, thus 110mm pipework was used. However, three separate sets of 110mm discharge pipework were installed to cope with the volume of water that would discharge off the roof space. (This was a lot easier said than done by the way, considering the size of the tanks, which made them awkward to carry. It took at least five people to carry one tank around the building!)

So how does the system work?

The existing downpipes were cut off and the team installed new 110mm white PVC pipes with holderbats. They ran the pipework on the left-hand side, the front side, and down the right side of the building. Because of the indentations of the building, as well as the existing air conditioners on the outside, it wasn’t possible to use 160mm pipework as it was too thick to allow for neat bends (or to fit behind the air-conditioning units). The bends on the 160mm would not only affect the neatness, but also the functioning and fitting of the system. Hence the selection of the 110mm alternative.

The left-hand side of the building has four downpipes that run around the building and into the second tank. Whereas in front of the building, two downpipes were picked up, feeding into a separate pipe that runs exactly symmetrical to the other, at the exact gradient to ensure a neat installation. This pipe was connected to the third tank. And then on the right‑hand side of the building, they ran a third pipe that picks up the remaining four downpipes; this pipework discharges into the fourth tank. The discharge pipes have been connected to the tanks in this order to ensure that the discharged water spreads evenly through the tank and is symmetrical.

To ensure that the system remains clean, leaf catchers have been installed on the downpipes to keep out leaves, twigs, and bird droppings, among others.

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Backups

An overflow has been installed on the tanks in times of excessive rain. Burger explains that the tanks have been spaced to cope with the worst possible rainstorm, following in-depth research he conducted on previous rainstorm patterns in the area from a reliable source.

Another safety feature is a float switch, which disconnects the electrical supply to the pump, so when the water in the tanks get too low this feature prevents the pump from burning out.

The tanks have level indicators to show how full they are so that people know when to open the valves to let water out.

Maintenance

Burgess has signed a maintenance contract to clean the system out twice a year. Maintenance is quite straightforward and involves stripping the tanks and washing them out. With the way the system has been designed, each tank can be isolated and cleaned individually, without affecting the rest of the system. Cleaning the entire system will take about two days.

A happy client

The entire project was completed in only a week. Once it was complete, it was handed over to a satisfied client on 24 July 2017.

Phase two will soon commence and will involve collecting the rainwater on the backside of the building by adding in an additional nine 5 000ℓ rain tanks with pipework to suit.

List of suppliers

  • Astore
  • Plumblink
  • HMS Pumps
  • Urban Rain Cell
  • TW Electro (Electricians)
  • Legends Hire (scaffolding)

Click below to read the October 2017 issue of Plumbing Africa

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