Clearing alien plants to improve water security

A programme to secure more run-off to major Eastern Cape dams is proving successful as water conservation efforts in the drought-stricken south kick into high gear, despite record rainfall to the north of the province.

One of the region’s significant water sources, the Kouga Dam – feeding Nelson Mandela Bay (NMB) metro and surrounds – hovers at just below 16% capacity (April 2023), with about 11 200 M ℓ of water available.

Gamtoos Irrigation Board (GIB), which manages the dam’s water, is amid a years-long governmentfunded drive to improve water security in the region by clearing alien invasive plant species in the catchment areas of dams supplying the area.

On average, the dam has been full every five years since its completion in 1969 but, due to the drought, it last overflowed in 2015.

“The state of our catchments is of utmost importance in terms of securing water that needs to reach our storage dams,” says Rienette Colesky, CEO of GIB. “This clearing of alien invasive plant species is an effort to be undertaken not just by the government, but all stakeholders – including farmers. It’s much, much cheaper than building dams.”

Research commissioned by GIB indicates that the baseline flow in catchment rivers could increase, on average, by up to 13 ℓ /day where alien plant species are removed in fynbos districts. Under current water restrictions in the Bay metro, that’s enough to supply a household for one month, as domestic water users are limited to 15 kℓ /month.

Over the past five years, GIB teams comprising 1 000 previously unemployed community members have cleared about 10 000 hectares of alien invasive plant species in dam catchment areas – the equivalent area of 20 000 rugby fields.

“These plants increase transpiration, and evaporation losses and absorb much more water from the ground than indigenous plants. They can reduce the flow of rivers and annual runoff, affecting the dams that supply water to the NMB metro — the Churchill, Impofu and Kouga dams,” says Colesky.

According to Edwill Moore, western area manager: Eastern Cape at GIB, the clearing of such invasive plants –predominantly black wattle species – has been significant.

“In the Kouga Dam catchment, around Louterwater, Krakeel and Joubertina, we have done new clearing of about 100 ha, and followup operations on previously cleared areas of 3 800 ha with 525 previously unemployed workers,” Moore said.

In the Churchill and Impofu Dam catchments, about 30 km upstream of Kareedouw to Churchill Dam, GIB teams have cleared – and continue to clear until 31 March – 2 256 ha of dense alien invasive trees in the riparian areas, as well as engage in follow-up operations on 2 273 ha of previously cleared areas, employing 600 previously unemployed community members, Moore adds.

“In the Kromme River (Churchill Dam catchment) and Dieprivier (Impofu Dam catchment), we are doing wetland restoration and rehabilitation,” says Moore. “This includes construction and maintenance of concrete weirs, to prevent any further loss of palmiet wetlands, as well as the establishment of indigenous wetland plants in the previously wattleinfested wetlands.”

According to Andrew Knipe, eastern area manager: Eastern Cape, the success of such projects lay in the continued work to clear the land of alien invasive plant species.

“The secret of the success here has been a consistent effort over many years. Alien vegetation clearing requires continuous follow-up and maintenance of cleared areas. This ongoing process requires proper systems to be in place,” Knipe says.