No immediate relief for Gaborone Dam
Mbongeni Mguni | Friday December 12, 2014 20:29
Along its catchment area and extending into South Africa through the South East District, approximately 200 smaller dams, many of which are located on private holdings, feed Gaborone Dam.
Of the smaller dams, none is as significant psychologically as Notwane Dam, which lies a few kilometres upstream of the larger dam. Thirsty residents of Greater Gaborone with a more than passing knowledge of the catchment area know to watch developments at Notwane Dam for any sign of inflows into Gaborone Dam.
With the Water Utilities Corporation (WUC) confirmation that Gaborone Dam has technically failed last week, all eyes are now on the first drop to cross Notwane Dam’s wall and fall onto the dusty rocks that have come to mark the supply to Gaborone Dam.
“It is accurate to say that Notwane Dam needs to overflow before any inflows may be received in Gaborone Dam,” the corporation confirmed in an emailed response this week.
“There have been no inflows into Gaborone Dam this season. WUC does not have the records, but we can confirm Notwane Dam hasn’t overflown yet this year.
“Notwane Dam, like other small dams in the catchment area, is not monitored. However, from our observations it has impounded some water since the current rainy season started.”
A Mmegi newscrew that visited the smaller dam this week found that while water levels appear healthy, more rain is needed upstream before a single drop climbs over the dam wall.
On the Notwane River side, the dam is a murky green with debris visible in the waters suggesting a shallow depth.
On its far ends, however, the water appears deeper, as the dam slopes inwards in the direction of the Lobatse highway.
The news that Notwane Dam is yet to overflow coincided with even more ominous warnings from the corporation on Friday, suggesting that residents of Greater Gaborone are in for even harsher times ahead.
“Please be informed that water supply in your area is fairly challenged this week. Current issues range from major pipeline bursts, pump breakdowns, power interruptions, and worst of all is the decline of Gaborone Dam to 5.2 percent.
This has resulted in low pressures and intermittent supply in some areas as our teams work around the clock to balance supply.
“As we ration to render supply more sustainable, we are also deploying water bowsers to relief (sic) wherever possible and also engaging the public via loudhailer and radio.”
The announcements immediately sparked angry finger-pointing at Gaborone Dam’s upstream dams, which have been blamed for limiting supplies to the 141 million cubic metre dam.
“Mathata ke matangwana,” one social media commentator posted in response to the warning.The issue of upstream dams starving Gaborone Dam of supply has been vigorously debated all the way up to Parliament, prompting firm denials from Water Minister, Kitso Mokaila.
“These dams have been there all along, yet the Dam has been filling up all these years,” he told Ntlo ya Dikgosi (House of Chiefs) earlier this year.
Mokaila, WUC and other water experts are all in agreement that the smaller dam’s impact is negligible and in fact, they assist to reduce silt from Gaborone Dam. The latter argument sounds feasible, as Gaborone Dam – by early last week – was still providing 14 million litres a day from a water level only one metre above mud.
Other dams, including the titans in the northeast, usually fail just below 10 percent when their water inflow points hit silt level.
According to former Minerals, Energy and Water Resources permanent secretary, Boikobo Paya, Gaborone Dam’s troubles are not linked to the multiple smaller dams in its catchment area.
Rather, they are the result of a catchment area dominated by small rivers incapable of adequately transmitting supplies, as well as the high offtake by users.
The current problems are also related to an odd weather cycle stemming back two years, he says.
“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.”
That something resulted in the drying up of Notwane Dam, which in turn would have to fill up and deliver in order to recharge Gaborone Dam. This cycle is repeated every water season, but inconsistent rainfall has meant the system has increasingly been disrupted.
Gaborone Dam was last full in December 2001 at exactly 100 percent, with its waters stretching up to the Yacht Club and visible from buildings in Commerce Park and Kgale Mews.
Since then, the disrupted recharge system has seen the dam dry up to 16 percent in December 2005, rise to 25 percent in January 2006 and climb further to 80 percent in March 2006.
The dam was last at its highest in April 2011 at 80 percent and it has been declining since. Last December, it was slightly above 10 percent before sliding to its current levels.
The dam loses approximately 2.6 percent per month, but the rate has been rising due to the summer heat and the negation of lower offtake rates owing to the natural depletion of the resource.
The confidence that water authorities had created ahead of the dam’s failure is dissipating in the wake of the latest warnings of “…major pipeline bursts, pump breakdowns, power interruptions…”.
Panicked residents are again turning to the issue of Gaborone Dam’s ‘baby brothers’, which they allege are surviving only by starving their elder sibling.
A study into the smaller dams is currently underway, which water authorities say will inform whether government needs to intervene and ‘unblock’ Gaborone Dam.
However, for now, official support is on the side of the farmers who own the dams.
“Private dams allow Batswana farmers to water their livestock, and they thus contribute positively to farmers’ livelihoods,” Mokaila told the House of Chiefs earlier this year.
“This issue of the dams blocking the water flow is something that we have heard about, and something that we will look into.”