Civil Engineering June 2022 | Vol 30 No 5

This was the most preferred and feasible solution as it will also enable the planned major dam rehabilitation works and repairs on the outlet tower and outlet pipeline to occur and to increase the demand of flow to the WTW. The work includes of a manifold chamber in which four 450 mm siphon pipes, each fitted with an isolation valve, will enter one pipe. Two gate valves will be installed on a scour pipe within the chamber as well as a 1.4 m nominal diam- eter, 180 m long transfer pipe, which will be trenched and buried, from the mani- fold chamber up to the connection point. A concrete encasing will be constructed for the pipes over the crest of the dam. The pipes cut through the dam crest and the materials removed from the embankment will be replaced with concrete. This will be a two-phase construction in order to main- tain the existing crest elevation at all times. Additional works include: Q Q A priming chamber on the crest of the dam, at the highest point on the siphon. Each of the four siphon pipes will be fitted with an air release pipe, as well as a priming pipe, all fitted within the priming chamber. Q Q A concrete platform upstream of the priming chamber. Q Q Installation of a 4 m wide, 30 m long and 1.3 m high steel cradle structure to house and support the four siphon pipes upstream of the dam crest. It will be fitted with buoyancy tanks for ease of installation and for raising the structure as and when required for future work and maintenance. Q Q A concrete cradle starting down- stream of the concrete encasing on the dam crest and ending at the toe dam wall. The cradle will house the four siphon pipes. All the construction works are being per- formed within close proximity of the dam wall, outlet works and within the original dam purchase area and pipe servitude of the Mthatha Dam, approximately 6 km northwest of Mthatha. PROJECT STATUS The project is currently 52% complete and is being implemented on a fast-track basis due to its critical nature. The system is considered very vulnerable, and urgent intervention is necessary to avoid com- plete failure with dire consequences. CONCLUSION Based on the investigations and findings, it was determined that constructing a bypass siphon pipeline will resolve the water short- ages in Mthatha caused by the pipe burst underneath the spillway return channel.  Civil Engineering June 2022 21 Site supervision team Installation of pipes using a crane Pipe reducer coating