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Alien vegetation removed from catchment areas to save every drop

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In a tactical move to save every drop of water in the Nelson Mandela Bay region, the NMBM is intensifying its alien vegetation clearing and catchment management work. First priority being the critical Impofu and Churchill Dams.

With the total dam levels standing at a critically low 12.62% as at 14 February 2023, the Municipality is working tirelessly to remove the alien trees that are fast encroaching into the actual dam basins and upper reaches of the catchment areas of these major dams, due to the ongoing severe drought.

Most of the alien vegetation comprises of Black Wattle and Port Jackson which are both very water hungry tree species with the regrowth being at an alarming rate. The Black Wattle trees is estimated to grow at 1.5m per year in ideal conditions like the dam basin as there is lots of water and fertile soil.

NMBM Infrastructure and Engineering Mayoral Committee Member, Cllr Dries van der Westhuizen said it has been proven that clearing alien vegetation is one of the most effective and cheapest ways of saving water.

“On average these trees can consume between 20-100 of liters of water per tree, depending on the size and age, per hectare this can result in a loss of 500 kilolitres per hectare in densely invested areas. Therefore, over the extensive areas that we are working in, this results in the loss of megaliters of water before making it into the actual dams. When we receive light rains or smaller amounts of rain, maybe less than 50mm there is very little inflow into the rivers and dams. Most of this water is actually consumed by these trees, this therefore has a huge impact on our water security in the region.”

“We are currently clearing 10 hectares per month at both these dams which effectively saves us approximately 2.5 – 5 Megalitres of water per month at each site. These trees drastically reduce inflow into the upper dam. Further to this, there is a lot of farming activity up stream of the Churchill Dam which entails irrigation of cash crops like cabbages and dairy farming which is also have a negative impact on the dam as the last remaining pools of water on the Kromme River is abstracted on a daily basis for irrigation.”

To date the Municipality has cleared 75 hectares of first phase bush clearing at each dam with two follow up herbicide spraying of regrowth which has contributed to the additional inflow into the dams when it rains. The follow up herbicide spraying is vital to ensure that all regrowth is killed off to prevent reinfestation. To date the City has spent R5,87 million at Churchill and R4,18 million at Impofu Dams over the past two and half financial years.

“At the Impofu Dam the water level has been at its lowest in history which has resulted in the encroachment of alien trees into the actual dam basin itself, which is not a good situation as this leads to the last remaining water reserves been consumed by these trees and they can cause problems later on when it does finally rain by blocking the intakes at the intake tower and spillway,” added MMC van der Westhuizen.

Earlier this year, NMBM decommissioned the Impofu Dam, which is the City’s biggest water supply.

The latest recorded DAM LEVELS can be found HERE.

https://straton.org.za/picture.php?/18728/category/96

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Alan Straton

Chief Cook, Bottle Washer and Broom Mechanic at MyPE
Passionate about Port Elizabeth and definitely NOT packing for Perth. Alan's ethos is epitomised in the words of Nelson Mandela; "I have fought against white domination and I have fought against black domination. I have cherished the idea of a democratic and free society. If need be, it is an ideal for which I am prepared to die." See more articles by Alan.