Wellington without water : impacts of large earthquakes

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Cousins, W.J. 2013 Wellington without water : impacts of large earthquakes. Lower Hutt, N.Z.: GNS Science. GNS Science report 2012/30 124 p.

Abstract: Metropolitan Wellington Region is vulnerable to large earthquakes. It is bisected by large active faults, and after a major earthquake on any one of them could become isolated because all of its supplies have to be transported along a small number of lifelines. All are vulnerable to earthquake damage. The potential for total loss of water and food supplies is real and, without mitigation, could render large areas uninhabitable for weeks to months. Models have been developed for the bulk water-supply system, including pipelines into Wellington City and water storage, and on the consumption side the buildings and people. In the model they were exposed to a suite of large earthquake scenarios, followed by computation of the numbers of breaks in the pipelines, the consumption of stored water, restoration of supply to the reservoirs and thus emergency-level water supply, and the expected shortfalls in supply. Outputs were the numbers of people without water, for how long, and the amounts of water that would be needed to meet the shortfalls. Only conventional sources of water supply were included in the modelling, because one of the desired outputs was estimates of the quantities of water that might need to be derived from unconventional sources, following large earthquakes near Wellington.Key findings for a magnitude 7.5 earthquake on the Wellington-Hutt Valley segment of the Wellington Fault (Wellington Fault Earthquake) were: • The bulk supply lines would suffer about 100 breaks and be rendered completely inoperative. • Stored water could last 2-6 weeks depending on the rate of consumption and assuming that 50% of the original stored volume would be lost immediately after the earthquake because of damage to reservoirs. • Bulk water would be restored progressively, taking about 3 weeks to reach Tawa (the suburb closest to source) and 10 weeks to reach Miramar (the suburb farthest from source). • For a consumption rate of 20 litres per person per day, the number of people without water would peak at 150,000 (80% of residents), and the shortfall in supply would peak at 3 million litres per day. For a consumption rate of 6 litres per person per day the peaks would be 50,000 people and 0.3 million litres per day. • The times for which people could be without water would be long, for instance 40,000 people without water for 40 days, and 80,000 for nearly 30 days. (auth)