Civil Engineering December 2021 | Vol 29 No 11

34 December 2021 Civil Engineering T he existing Durban Northern Aqueduct system operated by eThekwini Water and Sanitation (EWS) comprises of a network of potable bulk water supply pipelines that serve the northern areas of Durban. The system had, however, reached its maximum flow capacity at various sections of the trunk main system as a result of growth in demand from major new commercial and residential developments and urbanisation to the areas north of the Umgeni River. Bosch Projects was appointed by EWS to provide professional services required for the preliminary planning, detailed design and construction stages of the of the Northern Aqueduct Augmentation Project Phase 5, which comprises a new 11.7 km long, 1 200 mm diameter steel pipeline. It will provide a sustainable and assured supply of water to meet future demands in the northern areas of Durban. PROJECT DESCRIPTION The new Northern Aqueduct Phase 5 pipeline starts at the tie-in chamber at Pridley Road in Reservoir Hills, located just downstream of the Durban Heights Waterworks. From the bulk connection point, the pipeline descends into the Umgeni Valley, crosses the Umgeni River and traverses through the Newlands and Avoca Hills area, en route to Duffs Road, where it connects to the Phase 3 NAA pipeline, which continues from Duffs Road to the Phoenix 2 Reservoir. The pipeline route traverses through densely populated built-up areas, high traffic routes, major and minor roads, railways lines, high voltage electrical servitudes, existing underground services, and the Durban Metropolitan Open Space System areas. Several lower lying sections of the pipeline had to be designed for very high pressures from the Durban Heights supply reservoir, which is at an elevation of 277 m MSL, relative to the lowest elevation of 17 m MSL along the pipeline route. Allowance for water hammer and field test pressures required the continuously welded steel pipe to be designed for a maximum pressure of 3 300 kPA at its lowest point. Steel pipes of up to Grade 65 with a wall thickness of up to 12 mm had to be designed to accommodate these high pressures. Pipe specials such as tees had to be reinforced with crotch plates, with valves and fittings designed to withstand the high pressures. The pipeline route also traversed through areas of high soil corrosivity, in addition to the effects of stray currents from railway lines and high voltage overhead power lines. Rigid specifications were developed for suitable coatings and linings of the steel pipe. An impressed current cathodic protection system and alternating current mitigation was also designed and installed to protect the steel pipeline from the effects of corrosion and stray currents. RIVER CROSSING The pipeline crosses the Umgeni River via a bridge adjacent to the existing pipe bridge, situated approximately 9.6 km from the river mouth. The Umgeni River Pipe Bridge crossing comprises a 234 m long reinforced concrete box type bridge cross-section, incrementally launched and supported on five concrete piers and two concrete end abutments. The bridge has a 7 m wide deck allowing for the new 1 200 mm diameter pipeline, a future 1 000 mm diameter water pipeline and a future 500 mm diameter sewer pipeline. In addition, provision has been made for a 1.5 m wide pedestrian walkway The Northern Aqueduct Augmentation Project Phase 5 is now making its contribution to the sub- regional economic growth prospects in the greater Durban Metropolitan Region and in the KwaZulu Natal Province..  SANRAL SA I CE 2021 Nat i onal Awards Category: Techn i cal Excellence FINALIST Technical Excellence category (Sponsored by Maccaferri SA) KEY PLAYERS Client: eThekwini Municipality Consultant: Bosch Projects Contractor: Icon Construction Northern Aqueduct Augmentation Phase 5 Aerial view of the completed Umgeni River Pipe Bridge Crossing Pipeline construction along a steep embankment in Reservoir Hills