A reactive storm water control system on the University of Pretoria’s campus provides water for the botanical garden and doubles as a social space for students and staff.

A road at the University of Pretoria (UP), once a site with poor soil and little drainage capacity, is now host to a rainwater harvesting system that is fully integrated into the architectural design of the new Mining Engineering Study Centre.

The system is made up of a series of rain garden ponds and a storage tank, which feeds the 3.5ha Manie van der Schijff Botanical Garden. It is a bio-rich environment that has become a gathering place on campus and is an illustrative point for teaching green principles.

The system saves considerably on costs – a conventional upgrade of the storm water system would have been in the region of R4-4.5 million. The existing walls would have had to be waterproofed at an additional cost of R4 million.

“The rainwater harvesting solution solved these problems for around R1.7 million, a saving of over R6 million,” says Neal Dunstan, UP’s resident architect who oversaw the project with Jason Sampson, curator of the botanical garden.

The system harvests 17 000L for every 10mm of rain off the 1700m2 Study Centre roof.

“We have frogs breeding in the water, and when you have amphibians breeding, you know the water quality is good,” says Sampson.

Saving and reusing materials

“When Engineering 1 was constructed in the mid-1970s a hand-carved clay brick with a semicircular groove (a miniature half pipe) was used as cladding for the exterior walls,” says Dunstan. “We rescued as much of these bricks as possible and used them to edge the paving to channel water into the plantings. Then we used them as an anchoring edge for the liner and as access paths in the landscape.”

The old in situ cast concrete paving panels were lifted, broken up and used for cladding on the pond and pile cap walls. This created a habitat for aquatic and terrestrial life. It was also used as permeable paving.

The new paving materials came from suppliers that use waste material from platinum mining operations in the manufacture of their products.

“There were some existing copings on the exterior walls and use them as stepping stones in the landscape and emergency fire exits. All the rock that was excavated from the piling operations and pond excavations was reused in the landscape,” says Dunstan.

The team managed to save all the trees on site. When construction commenced, it was announced that a R25 000 penalty would be imposed on workmen should they damage a tree. “We were very impressed with how the contractor handled all of this,” says Dunstan.

“The project used very little concrete and cement. The structure consists primarily of steel, glass and aluminium.”

The soil for the ponds was sourced from a project on another campus. All compost was sourced from the university’s pilot composting project.

Specialised pond lining

The pond system is lined with a vulcanised rubber, which is chemically inert and can withstand sun for 40 years without UV degradation thanks to a high level of carbon black. The product, Firestone EPMD, has been tested as a liner for water reservoirs – it has a 300% stretch capability and can shift with any ground movement that occurs. It is also cheaper than concrete, can be reused should the ponds be moved, and is easily repaired.

This didn’t mean that it was without challenges. “Placing a semi rigid plastic sheet in a complex geometry such as this is almost impossible to achieve without a large amount of cut and welded panels,” says Paul de Luca of Belgro, which fitted the lining.

“This made EPDM the only viable choice. The EPDM liner is flexible, enabling it to easily conform to the flowing shapes.”

Treatment wetland and pumps

“The water is run through a bio-swale, which makes up the shallow areas of the pond, consisting of reed bed systems that do most of the cleaning,” says Sampson. “The open water bodies in the permanent and tidal ponds are more habitat-based.”

The water is then circulated through the system for 12 hours at night.

“The system reached full ecosystem stability by January 2014 and there is virtually no maintenance,” says Sampson.

The pump system is made of two borehole pumps that have lower electricity needs than regular pumps. The team considered using solar power for the pumps, but realised the pump would meet the end of its lifecycle before any meaningful payback could be made from a PV system.

“There’s a pump for the irrigation system and one that does circulation, and we don’t run them together,” says Sampson.

A place to teach green principles

“The UP Engineering Faculty trains a vast number of engineers in the country, and we’ve wrapped the idea of green engineering around them,” says Sampson.

The pond system has initiated interdepartmental co-operation on various projects, and has garnered academic interest, both nationally and internationally.

The system also has the potential to irrigate the whole campus. “We had three times the average rainfall in March 2014,” says Dunstan. “Our tank was filling so quickly that we had to pump water out and into the campus irrigation supply tanks. For nearly two weeks the irrigation needs of the whole campus were being met by this rainwater harvesting system alone.”

The full feature appears in the October – November 2014 issue on page 38. Images by Melanie Maré.