Preventative measures: Senteeko Dam, which is a privately-owned dam, is located near Barberton in
Mpumalanga. The spillway channel slab is slightly suspended. Photo: DWS
The department of water and sanitation is assessing and monitoring the Senteeko Dam in Barberton, which is at risk of failure, “to avert disaster”.
On Wednesday, spokesperson Wisane Mavasa said the department had been notified that a privately-owned dam, located near Barberton in Mpumalanga under the City of Mbombela local municipality, had been reported to be at risk of failure.
My Own Dam, publicly referred to as Senteeko Dam, is registered with the department’s dam safety office as a 26m-high medium size dam, with a storage capacity of 1.8 million cubic metres. It is owned by the Shamile communal property association and used for irrigation.
An evacuation alert from the GCIS Mpumalanga’s provincial office warned that residents and businesses downstream of Senteeko Dam (Barberton-Kaapsehoop) “must evacuate immediately due to imminent risk of dam wall failure, which could release 1.82 million cubic metres of water into the Suidkaap area”
Mavasa said the department had dispatched a team of dam safety engineers — working with the owner’s previously appointed approved professional person for the dam — to the site to conduct a technical assessment of the reported damage at the dam. It continued to closely monitor the earthfall embankment dam with a concrete spillway.
“Assessments and observations by the department’s dam safety specialists indicate that undercutting of the spillway channel is continuing, eroding and posing a threat to the stability of the structure,” Mavasa said.
“The spillway channel slab is currently slightly suspended or cantilevered. There is currently no overtopping of the dam wall and no excessive seepage has been observed on the earthfill embankment wall.”
The dam’s outlet valve is fully opened in accordance with the dam operating rules, however, because of increased inflows from the Die Kaap River, a tributary to the dam, the lowering of the dam water level has been minimal.
The owner of the dam is expected to start excavations of a side-channel spillway and this will be done under the supervision of the approved professional person, Mavasa said.
This side-channel spillway is intended to lower the water level in the dam, “thereby reducing undercutting of the spillway channel and preventing catastrophic failure of the dam”. It is anticipated that this exercise will proceed even if additional rainfall is experienced, Mavasa said.
The areas most likely to be affected have been identified as those in close proximity to the dam, particularly the Barberton Valley.
On Wednesday News24 reported that the City of Mbombela had taken urgent action to evacuate residents living near the dam because the wall was at risk of collapse due to heavy rainfall. Both Mpumalanga and Limpopo have been declared national disasters from devastating flooding in recent weeks that has killed 38 people, as of Wednesday.
Mavasa said relevant communications, warnings and evacuation processes are being implemented by the relevant authorities. Observations of the upper reaches of the Die Kaap River by the Inkomati-Usuthu Catchment Management Agency indicate that river flows have decreased since 19 January.
The Crocodile River, located about 60km from Senteeko Dam, is currently flowing within normal recent peak levels, she said.
“Any additional flows that may result from an unforeseen dam failure, should the current intervention measures not prevent it, are expected to have minimal impact on transboundary flows to Mozambique, which are currently elevated due to the recent flooding conditions.”
The department of water and sanitation has urged the public to avoid low-water bridges, unnecessary travel and activities near rivers.
In a Facebook post on Wednesday, Philip Minnaar, a Democratic Alliance councillor in Mbombela, noted an update from the De Kaap Irrigation Board “that the dam wall is presently still standing but is not stable and the structure is deteriorating. A technical team from Gauteng is on the way to assist in assessing the situation”.
“Please note that all safety warnings remain in place. Those close to the affected rivers, Suidkaap and De Kaap, should take the necessary precautions and, if needed, move to higher ground. Residential areas in Barberton will not be affected,” Minnaar posted.
“The Barberton Valley and upper reaches of the De Kaap River will be most affected. The De Kaap Irrigation Board will keep us updated on the situation.”