Donga repair work in final stages

GEORGE NEWS - A donga that formed over time at the Gwaiing Waste Water Treatment Works due to storm water run-off is being filled up, because it was posing danger for a chlorine contact tank located on its edge.

The donga (a dry gully, formed by the eroding action of running water) is near the final effluent discharge to the Gwaiing River and is one of two in the area.

The second donga will be repaired as part of the next project for the upgrading of the inlet and outlet structures at the works.Excavated gravel materials from civil construction sites that had been stored at the Outeniqua Waste Water Treatment Works, as well as excavated materials from current street construction projects, have been used to fill up the donga.

The material is being compacted to at least the density of the surrounding soil to avoid the forming of a weak spot that will erode again. Some pipework had to be relocated and redirected to allow for the construction.

The project is expected to be complete by the end of April. Geotechnical remedial works such as this one pose some challenges: firstly, to provide access for the construction machinery and secondly, to create a safe work environment.

To this end, the side slopes have to be trimmed so that slip failures, that cause danger to persons or equipment, will not occur.

The rainstorm on 11 March did not cause visible damage to the compacted filling. This is cause for some relief, as it indicates that the work being done will likely be a successful solution to the erosion problem, in conjunction with directing storm water away from the erosion area.

After these aspects are catered for, the project would not pose many challenges except that working in wet conditions is near impossible due to slippery conditions inside the work area.

The Gwaiing donga before the remedial works started.

The donga prior to the remedial works and how it currently looks with the remedial works underway. The suspended steel pipe is an existing cable sleeve and the rehabilitation is being done with the sleeve and cable intact.