Construction World December 2016

Special Mention

D

Public Private Partnerships

SAVANNA CITY RESERVOIR

In the freedom era the developers wanted to be part of the process of changing the housing landscape in South Africa. It wanted to create affordable housing that would be attractive to people from diverse cultural backgrounds. Its vision is of creating an environment where people could experience real quality of life in a safe, suburban space. On final completion it will provide more than 18 000 new homes. Aligning with its objective to build a sustainable city, Savanna City’s water supply and distribution system has been designed using the latest technology, aiming to limit water losses in the system to 10%, which is a very ambitious target. The reservoir is constructed using a ‘self-healing’ concrete. The super-absorbent polymers in the concrete expand and fill the crack, preventing any further loss. The concrete regains its liquid tightness and impermeability, so that it remains durable, extending the reservoir's lifetime and minimising maintenance and repair costs. Water network sectorisation is a very effective method to create a sustainable water system. In order to manage the water system efficiently it is divided into manageable zones, making it possible to monitor consumption of these zones independently. In addition, current leak detection costs are reduced as repair work can be focused in the high non-revenue water affected areas. Pressure management also limits the potential damage of the water related fittings and devices by reducing the maximum water pressure in the zones from 9 bar to 5 bar, therefore increasing the lifetime of the pipes and all related fittings and devices. Effective sectorisation and pressure management can contribute largely to the reduction of water losses. The installation of pressure reducing valves (PRVs) within the water distribution network is essential to relieve water pressure on the pipes. The higher or lower the pressure, the higher or lower Savanna City is one of the biggest developments of its kind ever undertaken in South Africa. But sheer size and return on investment were not the core motivations behind the vision for Savanna City and other developments.

the leakage. Valves can isolate incidents of pipe breakages and contamination, and limit the risk to the surrounding system. Savanna City opted for the use of automatic pressure reducing valves. These valves that are installed at strategic points in the network to control the water pressure, for example the PRVs will automatically reduce the water pressure during off-peak times and increase pressure at peak times. The professional team is also investigating the possibility to use the energy developed when the pressure is automatically reduced to generate electricity through a mini turbine system. The electricity developed, which could be regarded as 'clean' electricity, will be utilised for community purposes. Historically, the pipes used to distribute drinking water were made of plastic, concrete or metal (e.g. galvanised iron or copper). Poor quality pipes shorten the pipe lifetime and result in leaks, bursts and corrosion. Poor pipe quality may also facilitate the infiltration of chemicals into the drinking water. Upon embarking on this mammoth project Savanna City considered the size of pipes, the composition, the properties and quality of the available materials and technology to ensure an effective sustainable water system for the development, and chose Orientated Polyvinyl Chloride (oPVC) pipes. oPVC, for the main water distribution pipeline, is a world class technology that adheres to international standards. It is manufactured by realigning the PVC molecules through a process of biaxial orientation, which enhances the material properties – around twice the strength and ten times the impact resistance is achieved compared to traditional PVC pipes. oPVC pipes’ wall thickness can be reduced by up to 50% while maintaining the same pressure as that of the traditional PVC pipes. The result is that oPVC has a larger bore, offering greater hydraulic capacity and is more material efficient compared to other pipe options. It is also the most eco-friendly pipe system in the world as it requires less energy to produce than conventional PVC and other pipe materials. Considering the relative low weight, oPVC pipes are strong and durable. It stays strong through a range of temperatures, resulting in fewer burst pipes and is corrosion resistant which makes it ideal for water infrastructure durability. This initiative will have a major impact on how efficient planning, technology and experience can be combined to develop future sustainable cities.

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Project information • Company entering: Basil Read • Client: Savanna City Developments on behalf of Midvaal Local Municipality • Start date: 4 May 2015 • End date: 30 September 2016 • Main contractor: Basil Read • Project manager: Basil Read • Quantity surveyor: Basil Read • Consulting engineer: GIBB • Subcontractor: Basil Read Civils • Project value: R37 269 206 (excluding VAT)

Construction WORLD

DECEMBER • 2016