The Auckland region has a large number of dams for water supply, irrigation, farm waste treatment, stormwater treatment, sediment control, storing contaminated sediments and sewage treatment.
About 50 dams in the Auckland region are large enough to cause significant damage if they fail.
Dam failure can result from:
- natural factors such as earthquake and volcanism
- age (wear and construction techniques at the time of development)
- poor design, construction and operation.
Most dam failures occur within the first few years of construction. Most of Auckland’s large dams are more than 10 years old. Poor foundation materials, poor dam drainage, and weak construction materials are three primary factors associated with dam failure in New Zealand. The vulnerability of downstream features is considered prior to dam construction.
Dams that adhere to the Dam Safety Guidelines are constructed to a standard that will survive up to a one in a 200 year natural hazards event, such as an earthquake. Some dams are designed to provide protection from events with even lower return periods.
Impacts of dam failure
If one of the 50 large dams in Auckland were to fail, the flood wave would be characterised by high velocity, large water depth and flow close to the dam, reducing downstream.
Possible consequences of this are:
- flooding of land and communities located downstream of the dam with a consequent risk of loss of human life, and damage to structures, economic losses to businesses, farms and horticultural industries
- erosion and deposition of sediment over an area up to perhaps a kilometre long and several hundred metres wide
- failure of utility services, including roads, bridges and pipework located in the path of the flood
- reduced water supply to Auckland region if dam is a water supply dam.
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