Hutt City water supply following a Wellington Fault earthquake

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Cousins, W.J. 2015 Hutt City water supply following a Wellington Fault earthquake. Lower Hutt, N.Z.: GNS Science. GNS Science report 2015/55 38 p.

Abstract: Large earthquakes in central New Zealand are expected to cause extensive damage to buildings and infrastructure, along with many deaths and injuries. Cities most affected include Wellington, Lower Hutt, Upper Hutt and Porirua. It is expected that all major transport routes (air, sea, rail, and road) out of the main urban area, and many within the area, will be closed, and that there will be extended loss of bulk and reticulated water. Prior research has quantified the serious impacts on Wellington of a prolonged loss of bulk water supply, and has qualitatively described the situation in Lower Hutt. The benefits of providing new emergency-only groundwater bores at strategic locations throughout the valley floor of Lower Hutt have been demonstrated in maps. The Lower Hutt work has now been extended and quantified. Parts of the city not covered previously, i.e. the Western Hills, Wainuiomata, and the Eastern Bays areas, have been included in the modelling. Four main topics have been covered, (a) the distances that people might have to carry water in the first few weeks following a large earthquake, (b) potential shortfalls in water supply in various parts of the city, (c) improvements that several strategically-located new bores might make, and, importantly, (d) the numbers of people affected by each of the above. One finding was that there seems unlikely to be a serious shortfall in emergency-level water supply in Lower Hutt following a Wellington Fault earthquake. Whilst two suburbs could experience gaps of about five to ten days between the depletion of reservoir water and the restoration of emergency-level bulk supply, the gaps could be eliminated by lowering the personal consumption rate from 20 to 15 litres per person per day and minimising the loss of water from the reservoirs during the earthquake or, for one of the suburbs, by adding one emergency-only groundwater bore with a capacity of about 70 m3/d. A second finding was that with eight new emergency-only groundwater bores in place, 80% of the people of Stokes Valley and 90% of the valley floor people, would be within 1 km of a reservoir or groundwater source. It is realistic for water to be carried from source to home for distances of up to about 1 km. A third finding was, however, that there will be a serious problem with access to water in some areas. More than half of the people in the Western Hills and Wainuiomata are more than 1 km from their closest reservoir or groundwater sources. In the Eastern Bays, 80% of the people are more than 1 km from their closest source, with nearly 70% being between 2 and 8 km away. There seems no alternative to providing tanker transport of water to those people. About 20 average-sized tankers would be required, with another 12 or so being required on the valley floor in the absence of the eight new bores. Waterborne transport might be required for the Eastern Bays if the only access road is closed by landslides. (auth)