Rooftop revolution: UP converts parking lots into water harvesting systems

In a rooftop revolution for the University of Pretoria, the university now uses parking lots at its Hatfield campus for water collection.

This is part of the university’s commitment to optimal stormwater management, rainwater harvesting, and reducing its environmental footprint.

The parking lot project enables the collection of rainwater off a new lightweight roof that provides shade to cars parking in selected campus bays. The water collected will eventually help irrigate the Manie van der Schijff Botanical Gardens, which covers about 3.5 hectares of the campus.

The project, as with many other such projects, was designed around the idea of Sustainable Drainage Systems, which allow for a more sustainable approach to stormwater management.

“The opportunity to use the parking lot for rainwater harvesting came up when its roof needed replacement,” Jason Sampson, curator of the botanical gardens at the campus said.

He explained that its proximity 300 metres east of UP’s existing and award-winning rainwater harvesting garden made the project especially enticing and practically feasible.

The parking lot project will be fully operational once the system, consisting of lightweight roofing systems 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.

These are running alongside the Faculty of Engineering building. Excess water will flow into an existing 130 000-litre underground storage tank that was constructed along with the rainwater harvesting garden in the early 2010s.

“This tank is the centre of the Manie van der Schijff Botanical Gardens’ fully automated irrigation system,” Sampson said.

He has, over the past decade, ensured that many indigenous plants from the botanical garden’s collection now flourish outside its borders.

He has also 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 Department of Facilities Management.

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 explains that 17 000 litres of water can be harvested for every 10mm of rain that falls on the roof. The water is continuously circulated through plant-filled swales and ponds to be bio-filtered and cleaned.

Marié Badenhorst, landscape architect in UP’s Department of Facilities Management said the institution must comply with very specific stormwater management system requirements for public spaces, as set out by the City of 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.

Over the past year, projects launched at two of UP’s women’s residences have been very successful. One has seen the courtyard of House Madelief transformed into a stormwater drainage catch pit which sees surface run-off directed towards a central gravel seating area.

This allows water to infiltrate the soil while minimising surface run-off. Regular flooding of House Erica due to insufficient stormwater inlets has been addressed by installing a series of custom-designed drainage pits. These allow water to slowly seep into the ground, creating a pop-up pond whenever it rains.

zelda.venter@inl.co.za