Earthquake stability of the 200-litre emergency rainwater tanks used in the Wellington region

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Nayyerloo, M.; Mir, A.; Rodgers, G.W. 2017 Earthquake stability of the 200-litre emergency rainwater tanks used in the Wellington region. Lower Hutt, N.Z.: GNS Science. GNS Science report 2016/33 15 p. + appendices; doi: 10.21420/G2Q345

Abstract: Research by GNS Science has shown that restoring the supply of bulk water to the Wellington region following a major earthquake will be quite challenging. This is more so for Wellington City due to its long distance to the region’s water sources in Te Marua, Wainuiomata and Waterloo. It is estimated that it could take up to 70 days to restore the bulk supply to eastern Wellington City after an earthquake on the Wellington Fault. Greater Wellington Regional Council (GWRC) has investigated some options for meeting emergency water needs of the region following a major earthquake including a cross-harbour pipeline to supply water from Hutt City to Wellington City while the main pipeline is being repaired. A number of potential sites for storage of emergency water for supply to Porirua and Wellington’s northern suburbs have also been identified. Hutt and Upper Hutt Cities are much closer to the sources and restoring the supply of bulk water to them will be less challenging compared to Wellington City. In parallel to the GWRC efforts, the Wellington Region Emergency Management Office (WREMO) has partnered with a provider of water tanks, The Tank Guy, to make 200-litre emergency rainwater tanks to be connected to downpipes in houses for rainwater collection to assist with the post-event emergency water needs of the Wellington region. While the rainwater tanks are being promoted as a viable means of collecting and storing emergency water, very little research exists that explores the stability of these tanks to hold the water during severe shaking that is expected from a rupture on the Wellington Fault. The present report looks into this potential issue through developing analytical models of the dynamic response of the rainwater tank to seismic shaking. The adequacy of the retaining strap, which is provided as part of the installation package, in preventing the tank from toppling during a large earthquake, is also discussed. The research also identifies the optimum position for the retaining strap along the tank height to provide maximum stability during shaking. (auth)