Critical factors for restoration of water supply pipelines in the Hutt City, New Zealand after a magnitude 7.5 earthquake from the Wellington fault

摘要

The water distribution network for Hutt City consists of nearly 700 km of pipes, 6500 valves, 4000 hydrants, and 21 reservoirs located on the surrounding hills. The bulk water is pumped to hillside reservoirs from trunk lines and some water for the city is also taken from artesian wells located on the floor of the Lower Hutt Valley. The Wellington fault, capable of generating an MW=7.5 earthquake with a return period about 600 years, lies at the western side of the Hutt Valley and passes through both residential and commercial areas. The shaking intensity from this earthquake is expected to be MMI 9 (where MMI is Modified Mercalli Intensity) or greater over the entire City. We simulate the damage to the pipelines using fragility curves derived from overseas data, which are functions of MMI, material type and soil condition. We use a Poisson process to generate damage locations along a pipe, given an expected break rate, then repair the network using an algorithm based on a likely restoration sequence. First all valves are closed. Then starting from a reservoir, a valve is opened and pressure is established. We account for pipe repair time (a function of pipe diameter), opening and closing of valves, checking hydrants and traveling from one location to another. Multiple crew repair parties are used. In the present study, we have excluded the repair time required for damages to the bulk supply pipes (trunk lines) that carry water from water treatment plants to the reservoirs of the surrounding hills in the Hutt City, the reservoirs, wells and the customers own pipes that link individual properties to the council-owned distribution system