Augmentation of Markman Main Sewer Phase 3

The Augmentation of Markman Main Sewer Phase 3 entailed the construction of a 1000mm diameter HDPE lined reinforced concrete sewerage pipe from just beyond Settlers Bridge, the N2 crossing of the Swartkops River, to the Fish Water Flats Wastewater Treatment Works (WWTW).  Phase 1 and Phase 2 of the augmentation project was also completed by Africoast Consulting Engineers through earlier design and implementation projects. 

Phase 1 of the augmentation entailed the construction of a 1000mm diameter GRP sewer main from the Bluewater Bay Grit Chamber to the Settlers Bridge and the construction of an 800mm diameter pipe across the Settlers Bridge.  Phase 2 entailed the lowering of the stormwater pipe/system crossing the N2 in the vicinity of the Grit Chamber to allow the completion of the new 1000mm diameter pipe at this location.

The current and future sewage flow in the Markman Main Sewer exceeds the capacity of the existing sewer from Blue Water Bay to the Fish Water Flats Wastewater Treatment Works.  The project aimed to alleviate this problem by providing a new sewer with the capacity to convey the full current and future peak flow in this section of the Markman Sewer, whilst retaining the existing sewer to serve as backup.  A bypass chamber was constructed at the Grit Chamber to divert the sewage flow into either the new or the existing main sewer from where it flows to the treatment works.  This will reduce the risk of sewage spillage into the environmentally sensitive Swartkops River Estuary, by providing adequate conveyance capacity and a diversion sewer to convey the flow when maintenance to either of the two sewers is required.

The project had proven to be a challenging project with elements incorporating strict environmental restrictions working within the Swartkops River Salt Marsh. The area was classified as a designated Critical Biodiversity Area due to the presence of critically endangered fauna and flora, including the area functioning as an ecological process area. The pipeline had to be installed in a very narrow 15m wide corridor and furthermore the pipeline construction occurred under marsh conditions. This required the installation of a continuous well pointing system to lower the water table to the extent where the pipes could be installed in relatively dry conditions. The sections of pipeline at deeper invert levels required the additional installation of pilling sheets to retain the excavation embankments and prevent it from collapsing onto the working space.

The construction of the pipeline was completed within 9 months ahead of schedule, and given the difficult conditions was a great client and professional team accomplishment.  The innovative and holistic approach to the design and construction of the pipeline and associated structures ultimately resulted in the successful construction and implementation of the project.