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, with the first priority being
the critical Impofu and Churchill Dams.
With the total dam levels standing at a critically low 12.62% as at February 14, 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 are estimated to grow at 1.5m per year in ideal conditions like the dam basin as there is lots of
water and fertile soil.
MMC for Infrastructure and Engineering, 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 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 infested 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,” he said.
“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. Furthermore, there is a lot of farming activity upstream of the
Churchill Dam that entails irrigation of cash crops like cabbages and dairy farming which 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 re-infestation.
The metro has also spent R5,87 million at Churchill and
R4,18 million at Impofu Dams over the past two and a half financial years.
“At the Impofu Dam the water level has been at its lowest in history. This 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 being consumed by these trees. This can later cause problems when it does finally rain by blocking the intakes at the intake tower
and spillway,” Van der Westhuizen added.
Earlier this year, the NMBM decommissioned the Impofu Dam, which is the metro’s biggest water
supply.
Other dam levels are as follow:
Kouga Dam 12.65 %
Churchill Dam 26.51 %
Impofu Dam 6.91%
Loerie Dam 45.24 %
Groendal Dam 13.70 %
TOTAL 12.62 %.
ISSUED BY THE NELSON MANDELA BAY MUNICIPALITY COMMUNICATIONS OFFICE
