TECHNICAL
ISOLATION OF A CRITICAL ASSET IN THE WATER SUPPLY NETWORK
Craig Rieck Fraser Coast Regional Council
How do you take the largest water reservoir in your network offline for a period of three months for re-lining? The short answer is you bypass it. The reality (or the long answer) is that is takes 12 months of planning, trials and teamwork to ensure water security. The Urraween Reservoir at 33 ML is the largest potable water storage in the Hervey Bay water supply network and is the main buffer storage for the majority of Hervey Bay suburbs. The reservoir is also the lowest in the network and has a pump station to boost the flow to the final gravity supply reservoirs before the reticulation network. The configuration of the reservoir site pipework has all flow entering the reservoir before being able to be pumped. Isolation of the reservoir would eliminate the existing pump station and limit flow to gravity, which was deemed to provide insufficient security of supply. The reservoir is an earth-based dam style reservoir with a HDPE floor liner and geomembrane floating cover. The floating cover on the reservoir had reached the end of its useful life (22 yrs) and required replacement. To
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Figure One – Photo of Urraween Reservoir (prior to refurbishment).
achieve this the reservoir had to be removed from service for a period of 3 months while the liner and cover material were removed and replaced. The complexity was that, since it was 22 years since the last time this asset had been taken offline, there was no documented process to ensure water supply security. This paper covers the process that Fraser Coast Regional Council went through to ensure the security of water supply during the period the reservoir was offline for refurbishment. The Urraween reservoir is a critical asset in the potable water supply network for the Hervey Bay town site. The reservoir is the largest in the network and provides the following functions: • Acts as buffer storage for peak consumption demands and as contingency in the event of a trunk main or treatment plant failure. The reservoir provides sufficient storage for approximately 2 days in summer and up to 5 days in winter
ENGINEERING FOR PUBLIC WORKS | JUNE 2021
• Provides a secondary supply to the two adjacent hospitals in the event of a failure in the reticulation network. Back supply is via a dedicated emergency pump station located on the reservoir site • Maintains water quality via the dosing and monitoring of chlorine, as it is the only chlorine dosing station between the treatment plant and the customers • Delivers boosted pumping of water to the reservoirs that supply customers via gravity, complicated by the fact that all water must flow through the reservoir to get to the pumps • Bypass of the reservoir was via gravity only, with no pipework in place to allow pumping The reservoir was constructed in 1990 from an ex-quarry site with part fill embankment and part excavation construction. At 138m long, 67m wide and 6.3m deep it holds a total of 33ML of potable water. It is a membrane lined earth reservoir made up of a floor liner from High Density
