Is there life after Gaborone Dam�s death?
Mbongeni Mguni | Friday October 10, 2014 17:09
According to Boikobo Paya, the origins of Gaborone Dam’s present troubles are not as clear as they appear.
“We had very low rainfall in 2012/13 across the country but for the first time in a long time in that year, the eastern corner received something better than others which was a bit surprising,” Paya told the Botswana Society recently.
“In the 2013/14 season, we generally had reasonable rainfall of normal to above normal, but this time that eastern area suffered. Gaborone Dam’s catchment area looked like the Kgalagadi on the heat maps and it was profoundly clear that something was happening there.”
Part of that “something” lies in the nature of Gaborone Dam’s catchment area, which consists of small rivers incapable of adequately transmitting supplies as well as the high offtake or abstraction.
In fact, on average, Gaborone Dam drops by 2.6 percent every month and breached “Drought Phase I” in June 2012. Drought Phase II was breached in December 2012 and Drought Phase III in February 2013. Each Drought Phase triggers water demand management responses such as restrictions and rationing, but unfortunately for Greater Gaborone, there is no Drought Phase IV.
Instead, Drought Phase III is followed by siltation or a situation when the waters reach mud level, a development expected anytime between now and the next two months.
Meanwhile, Paya’s colleague and Met Services director, Thabang Botshoma, says the first rains in Gaborone Dam’s catchment area are expected mid-November.
“The last rainfall season was a good one for most of Botswana but we all know very well the Gaborone Dam story and what happened in terms of rainfall over the south-eastern parts of the country,” Botshoma says.
However, Botshoma expects that on average between October and December, the Greater Gaborone area will receive above normal-to-normal rain; meaning rainfall amounts could be beyond the 190 millimetre level throughout the period.
During the second half of the rain season, between January and March, however, the Greater Gaborone area will have “an increased likelihood” of below normal to normal rains.
Apart from the constricted catchment area as a result of the small rivers, it is debatable whether these rains will save Gaborone Dam from failure, as statistically this debate is untested due to the simple fact that the Dam has never failed before.
During the 2005/06 drought, Gaborone Dam reached 16 percent in December 2005 but recovered to about 25 percent by January 2006. In March 2006 it had topped 80 percent.
However, last December the Dam was slightly above ten percent and only gained about five percentage points up to April, when it then began sliding to the current 7.4 percent.
Despite the gloomy picture, Paya and other water authorities are confident that the taps will not run dry. At present, the Greater Gaborone area requires approximately 110 million litres of water a day under rationing, which is supplied 48 million litres by Gaborone Dam, 60 million litres through the North South Carrier from Letsibogo Dam, 40 million litres from Molatedi Dam in South Africa and Bokaa Dam as well as the Ramotswa boreholes.
When Gaborone Dam fails, the burden will shift largely to the North South Carrier where supplies from Letsibogo Dam and more recently, Dikgatlhong Dam will flow southwards.
A particularly troublesome 26-kilometre stretch near Palapye on the critical pipeline has also been reinforced with steel to reduce the costly bursts of previous years.
In addition, plans are underway to install an additional pump station along the pipeline to increase water flow, while also finalising the Masama wellfields in Kgatleng which will provide 33 million litres per day.
“If the Dam fails, which can happen anytime, we have a little bit of room due to the rationing but it does get very tight if for any reason anything happens to interrupt us from Letsibogo 600 kilometres,” Paya said.
“Anything can happen, from a pump failing to vandalism. Once that happens, the question will be how fast we can fix the problem. We would have a serious problem.”
Following the reinforcement of the North South Carrier, most water officials say they are “100 percent” confident of its ability to deliver, outside of pump failures and vandalism.
Vandalism, in particular, is rife along the 600-kilometre pipeline with some unscrupulous farmers breaking into pump stations and leaking water for their livestock. At one particular station, bold vandals etched the words, “Re ja metsi a Letsibogo” at the scene of their crime!
Much will also depend on the forthcoming rain season, which if low will lead to the failure of Bokaa Dam and the removal of its 20 million litres per day to Greater Gaborone.
If above normal, the rain will replenish Gaborone Dam to some extent, recharge the Ramotswa and Masama wellfields, quench Bokaa and slowly return the situation to stable.
In the meantime, water authorities say one eye should be kept to the skies for rain and another on any opportunities for further water conservation.