Major dams face collapse in Zimbabwe
Tabitha Mutenga and Andrew Kunambura
A HUMANITARIAN crisis is looming countrywide amid revelations that Zimbabwe’s major dams are in urgent need of refurbishment which, if further delayed, could see them collapsing, the Financial Gazette can exclusively report.
A survey commissioned by the Zimbabwe National Water Authority (ZINWA) has revealed that the country’s major dams have not been inspected for over a decade, with government citing lack of funds as the major reason. It says at least US$33 million is now required to maintain and refurbish the dams since they now pose a serious danger to human life and infrastructure.
Dams are supposed to be thoroughly inspected and maintained after every five years.
The survey was conducted by a South African consultancy company known as ARUP, with funding from the World Bank.
It was carried out on a sample of 25 major dams located on the country’s seven catchment areas.
Zimbabwe has a total of 10 000 dams.
The survey disclosed that three of the 25 dams in the sample needed urgent attention, critically the replacement of valves.
Half the dams have inadequate spillways.
Seventeen dams, including Osbourne (Mutare), Ruti (Gutu) Smallbridge (Mutare), Manjirenji (Chiredzi), Muzhwi, Bangala (Mwenezi) are on the red list with antiquated valves and crumbling inlet spillways, which need immediate attention while Mutirikwi, Langwalala, Rusape, Manyuchi and Ngezi have walls or embankments that are in serious danger of collapsing.
Ngezi and Langwalala walls are in a state of emergency, which means human life is in immediate danger. The walls are leaking.
The report also warns of horizontal cracks developing on the Mutirikwi dam in Masvingo.
“Lungwalala Dam left and right bank seepage is significant and needs more detailed geotechnical investigations followed by urgent remedial works,” reads part of the report.
“Mechanical maintenance at all dams has been significantly neglected, mainly as a result of insufficient budgeting and funding. Funds should be urgently made available for both the critical replacements and for the routine annual maintenance,” it says.
ZINWA oversees the operation and maintenance of all the major dams under the Water Act (Chapter 20:24) of 1999, which compels it to carry out five-yearly inspections of the dams. However, all of Zimbabwe’s dams except Kariba were last inspected in 2005.
The dam safety budget has not received any fiscal support over the years, making it difficult for ZINWA to comply with the requirements under the Water Act.
This violation of safety procedures, warns the survey report, could result in dams collapsing and triggering massive disasters.
Sensing possible dangers, government has devised a user pays policy whereby ZINWA carries out dam safety inspections as well as the required maintenance and repairs through revenue collected from users who include industry, mining companies and farmers.
But the model has dismally failed to work as users heavily default on payments. This means dams continue to wane and could give in if maintenance is not done urgently.
ZINWA dam designs and construction manager, Taurayi Maurukira, responding to the survey report, said the situation should not be allowed to continue.
“There is a human price to pay for it,” he said.
“Dams serve as water terminal storage facilities and when they fail, water can come rolling down homes,” added the water engineering expert.
“When you let loose water, it’s a deadly weapon. It’s a battlefield but unlike in war where you can hear guns from a distance and you can run to safety, this time, you won’t hear anything. You will be struck suddenly. So we need to maintain them all the time,” he warned.
ZINWA board chairman, Michael Tumbare, said there was a real danger of the dams bursting.
“Twenty-five dams were sampled and out of these came the grim statistics. The worst possibility is they can burst and we risk losing the dams and many lives,” he said.
“Right now, what we need to do is for all of us to understand that there is infrastructure that needs to be maintained. We need to start to adhere to maintenance plans because at present, the country is in a sorry state,” said Tumbare, a University of Zimbabwe civil engineering lecturer.
In the event of dam failure, tonnes of water could crash through entire towns and villages, leading to loss of human life and destruction of infrastructure. Wildlife and livestock would also be under threat.
This is because of the destructive power of the flood wave that would be released by the sudden collapse of a large dam.
Dam failure can be caused by a weakening wall (also known as embankment in civil engineering terms), malfunctioning spillways and, more significantly, ageing valves.
Research indicates that two thirds of all recorded dam failures have been due to hydraulic inadequacy.
While equipment malfunctioning and operating errors have been to blame, inadequate spillway capacity leading to overtopping was the principal cause.
There are many previous cases where damn failure has proved to be catastrophic.
The Johnstown dam failure of May 31, 1889 in Pennsylvania, United States, is considered the worst case of dam failure disaster in history.
The water crashed down the valley, sweeping trees, rail cars and entire houses in its path.
By the time the 20 million tonnes of water reached Johnstown, it was carrying even more debris. The mass hit the city, flattening everything in its path and killing 2 200 people.
Another example is the Bento Rodriguez dam disaster which struck Brazil in November last year when an iron ore tailings dam collapsed in the city, causing massive flooding and 17 human deaths.
It also triggered a massive environmental crisis which needed international response.
A subsequent inquest found that authorities had been warned about the possibility of the dam collapsing as far back as 2008 but did not act.
In 1972, in West Virginia, a coal slurry dam with an inadequate spillway collapsed during a period of moderately heavy rain.
This resulted in the death of 125 people in Buffalo Creek Hollow.
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