The Gamtoos Irrigation Board’s (GIB’s) years-long government-funded drive to improve water security in the Eastern Cape by clearing invasive alien plant species in the catchment areas of dams supplying the region is proving successful.

The board manages one of the region’s significant water sources, the Kouga dam, which feeds the Nelson Mandela Bay metro and surrounding communities.

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

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

On average, the dam has been full every five years since its completion in 1969; however, owing to drought, it last overflowed in 2015. Currently, the dam maintains just above 12% capacity, with about 11 200 megalitres of water available.

GIB research indicates that the baseline flow in catchment rivers could increase on average by up to 13 kilolitres a day where alien plant species are removed in fynbos districts, which, under the current 15 Kℓ/month domestic water use restrictions in the Mandela Bay metro, is enough to supply a household for one month.

“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 yearly runoff, affecting the dams that supply water to the Nelson Mandela metro, [namely] the Churchill, Impofu and the Kouga dams,” Colesky continues.

GIB area manager for the western part of the Eastern Cape Edwill Moore adds that 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 follow-up operations on previously cleared areas of 3 800 ha with 525 previously unemployed workers,” Moore says.

In the Churchill and Impofu dam catchments, about 30 km upstream of Kareedouw to Churchill dam, GIB teams have cleared 2 256 ha of dense alien invasive trees in the riparian areas, as well as engage in follow-up operations on 2273 hectares of previously cleared areas, employing 600 previously unemployed community members.

“In the Kromme River [Churchill dam catchment] and Dieprivier [Impofu dam catchment], we are doing wetland restoration and rehabilitation. 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 wattle-infested wetlands.”

The success of such projects lay in the continued clearing of invasive alien plant species, says GIB area manager for the eastern part of the Eastern Cape Andrew Knipe.

“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.”