Pretoria University's rainwater harvesting transforms parking lots

As South Africa observes National Water Week from March 20-26, the University of Pretoria (UP) has unveiled an innovative rainwater harvesting system that transforms campus parking lots into water collection points.

According to the curator of the Manie van der Schijff Botanical Gardens, Jason Sampson, the opportunity to use the parking lot for rainwater harvesting came up when its roof needed replacement.

“Its proximity 300m east of UP’s award-winning rainwater harvesting garden made the project especially enticing and practically feasible,” he said.

The water collected will eventually help irrigate botanical gardens which cover about 3.5ha of the campus.

The project was designed around the idea of sustainable drainage systems, which allow for a more sustainable approach to stormwater management.

The university said the parking lot project will be fully operational once the system, consisting of lightweight roofing and permeable paving feeding into an underground catchment (with an integrated rainwater infiltration zone), is connected via piping to the nearby rainwater harvesting garden and its series of ponds running alongside the faculty of engineering, the built environment and IT’s engineering 1 building. 

Excess water will flow into an existing 130,000l underground storage tank that was constructed along with the rainwater harvesting garden in the early 2010s.

Sampson, who has over the past decade ensured that many indigenous plants from the botanical garden’s collection now flourish outside its borders explained: “This tank is the centre of the Manie van der Schijff Botanical Gardens’ fully automated irrigation system.”

He has planted various edible plants across UP’s eight campuses.

Sampson conceptualised the Rainwater Harvesting Garden in the early 2010s along with Neal Dunston, the then resident landscape architect in UP’s facilities management department.

The garden showcases aquatic ferns and other notable plants such as papyrus and sacred lotus, which do more than beautify a space that was once covered by roads and hard surfaces. The man-made wetland provides an innovative, useful and more cost-effective way to manage, retain, filter and recycle the deluge of stormwater that runs off rooftops, parking lots and other hard surfaces such as pavements around it during the region’s high-rainfall summer storms.

Sampson said that 17,000l of water can be harvested for every 10mm of rain that falls on the 1,700m² study centre roof alone.

He said the water is continuously circulated through plant-filled swales and ponds to be bio-filtered and cleaned.

When it was conceptualised in 2013, the hope was that the garden would merge landscape and building, serving as a “living laboratory” to inspire similar concepts across the university.

According to Sampson, the garden is regularly used for teaching and is a valuable source of plant material for many research projects.

He notes that studies on medicinal water plants have resulted in many spin-off advantages, such as the publication of a book. The microbial life in the wetland soil is also being studied.

The garden has inspired similarly beautiful rain harvesting ponds at UP’s Future Africa campus and the engineering 4.0 building, with water also being used for irrigation.

A sustainability specialist at the facilities management department, Ilze Ueckermann, said rainwater harvesting and incorporating indigenous and/or edible “giving gardens” offer a holistic approach to sustainable water management.

“These strategies conserve water and enhance biodiversity, food security and climate resilience. They allow the university to use water sustainably, while ensuring that stormwater that would have in the past just run away is retained longer, ensuring infiltration into the soil and less damage to infrastructure,” Ueckermann said.

A landscape architect in the facilities management department, Marié Badenhorst, said the institution must comply with very specific stormwater management system requirements for public spaces, as set out by Tshwane’s roads and stormwater department.

She explained that the implementation of various localised attenuation facilities to help stormwater better infiltrate into the soil has proven to be a cost-effective way of lightening the load of urban drainage systems during downpours.

 “There are also the added advantages of water being filtered and groundwater being replenished,” she said.

The university notes that over the past year projects facilitated by facilities management at two women’s residences have been successful.

“Small interventions like these reduce the risk of flooding and damage to UP facilities, and they form an integral part of our stormwater management plan, which is part of the UP 2030 spatial development plan,” Badenhorst said.

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