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An eight-month, R25-million rehabilitation of Emmarentia Dam, one of Johannesburg City Parks and Zoo's flagship properties, is under way.

R25m Emmarentia Dam rehabilitation under way
The rehabilitation project will ensure both the integrity of the dam and the safety of properties downstream.

The 103-year-old dam is located on the Westdene Spruit, a tributary of the Jukskei River, and combines with the adjacent Johannesburg Botanical Gardens to form an 81-hectare outdoor recreational venue that is highly popular with residents across the city.

The dam's ageing infrastructure, erosion, corrosion and several significant floods have necessitated the City's investment in proactive maintenance of this landmark.

Rehabilitation, which is being carried out by the Johannesburg Roads Agency (JRA), started in April and is expected to be complete in January 2016.

According to Mpho Kau, Acting Managing Director of the JRA, a recent, comprehensive investigation had confirmed that preventative maintenance and flood retention protection was needed, both to safeguard the dam's integrity and to ensure the safety of residential properties downstream.

The investigation revealed that subsiding had put the stability of the dam wall slope potentially at risk, Kau said in a statment.

It also indicated "that urgent repairs are required to the return channel, as a major flood could undermine the existing gabion and concrete walls, causing significant structural damage, while continued erosion could expose the banks and possibly undermine existing municipal roads located in close proximity to the right-hand side of the return channel".

Emmarentia Dam: a popular outdoor recreational venue
Geese, dabchicks, moorhens and other water fowl share their home and around Emmarentia Dam with canoeists, kayakers, sailors, anglers - as well as those who take their outdoor exercise in a more leisurely fashion.

In addition, the section of Olifants Road that crossed the dam wall (running along the crest of the dam's embankment) had also been affected by possible leakages within storm water inlet structures, which required repairs and reconstruction of the road.

This section of Olifants Road was closed in July to allow this work to be done, and is only expected to open again on 10 December.

The project will include:

  • Improving the flood prevention facility system to protect properties located downstream of the dam from flooding. This will include excavating and repairing the pipework and surrounding soil at the stormwater structures located along the dam, altering outlet structures, repairing the box culvert outlet, widening the control section, and constructing a gabion wall on the eastern side of the outlet.
  • Repairing the dam wall by strengthening the stone protection layer.
  • Addressing the obstructions currently located in upstream of the culvert spillway which decrease its capacity. This will require the removal of the canoe storage shed located in the immediate vicinity of the spillway inlet, as this poses a serious public safety risk.
  • Removing trees located on the side of the left bank, as well as a large Plane tree on the upstream embankment, whose continued growth could threaten the embankment's integrity.
  • Implementing protection measures to prevent future erosion caused by high volumes of flooding water. These will include gabion wall reconstruction and repairs, as well as reconstructing the bottom of the channel.
  • Building a concrete wall where the channel approaches the roadway, in order to prevent damage to the roadway, and reconstructing Olifants Road.
  • Repairing a portion of the wall which is subsiding next to the bridge support.

The JRA will also negotiate with the Canoe and Sailing clubs on alterations to the configuration of the two clubs.

"We look forward to the completion of these preventative measures, which will ensure the dam has the capacity to convey a flooding event of the 25-year recurrence flood peak value, and we request the community's cooperation while work is underway, as all rehabilitation will be undertaken without draining the dam," Kau said.