Fight against aliens helps fill Bay dams

VLEI REPAIR: A team employed by the Gamtoos Irrigation Boad works on a Kromme River wetland

Rehabilitation of wetlands and removal of plants replenishes dwindling water supplies

The authorities are upping the ante against the alien invasion of the Kromme and Kouga river catchments in a bid to free up more water to replenish the drought-stricken dams feeding the Nelson Mandela Bay metro.

The two projects, which together employ 350 people, are focused on clearing black wattle and other aliens, and rehabilitating wetlands – all aimed at improving water flow into the Churchill, Mpofu and Kouga dams.

The projects are being implemented by the Gamtoos Irrigation Board in Patensie, two among a swathe of similar projects that the board implements across the Eastern Cape.

Funding from the Department of Environmental Affairs is channelled through the department’s Working for Water programme.

The Kouga River flows into the Kouga Dam northwest of Patensie and clearing teams are working through a whopping 282 000ha from Haarlem in the Langkloof downriver to the dam, the board’s western region manager Edwill Moore said yesterday.

The Kouga Dam supplies the vegetable irrigation farms in the Gamtoos Valley as well as the metro.

The Kromme flows into the Churchill Dam west of Humansdorp and then downstream into the Mpofu southwest of the town.

Although the focus is on just 40 000ha, the board has contracted 13 teams – 12 in the Kouga – and the focus is on rehabilitation of the peat wetlands as well as alien clearing.

“Peat has the capacity to store up to 20 times its weight in water, which allows water to remain in the system longer,” Moore said.

As the river flow loses speed through the wetlands the sediment it is carrying settles and it emerges cleaner, improving the quality of the water running into the dams.

To fix degraded peat vleis, indigenous palmiet is reintroduced and simple weirs and wire nets or rocks are installed.

The board’s financial manager, Rienette Colesky, said it was important especially in this time of drought that the public understood the challenge to water supply posed by alien invasives and eroded wetlands and the work being done to address these challenges.

To do the work, the board contracts operators who tender for blocs of land within the focus area and, in turn, employ teams of local people. In the Kouga and Kromme catchments, wattle, bluegums and hakea trees originally from Australia and pines from Europe are targeted.

The workers use chainsaws and slashers to fell or ringbark the trees and herbicide is applied.

Regrowth depends on the species and the area but return visits are made until regrowth is down to 5% or less.

Senior NMMU botanist Professor Richard Cowling, who has worked extensively on alien eradication programmes, said the premise that alien trees sap water resources was well established.

Their deep roots and greater mass in the slight, low fynbos of the upper Kouga and Kromme made these demands especially skewed, he said.

“We’re in a desperate situation with the drought and down to base flow in the rivers,” Cowling said.

“But where aliens are using even this up, nothing is coming down to go into our dams.

“These catchments supply the most crucial ecosystem service in the form of clean, fresh water so we need to invest in this work.

“Considering the amount of aliens we still have to eradicate, there are still not enough resources going into it.”

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