Technological (man-made) hazards

Dam failure

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.

Approximately 50 dams in the Auckland region are large enough to cause significant damage if they failed. Dam failure can result from:

• natural factors e.g. earthquake, volcanism etc
• 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. In Auckland the majority of large dams in the region 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 physical vulnerability of downstream features is determined prior to the dam construction.

Dams that adhere to the Dam Safety Guidelines are constructed to a standard that will survive up to a 1 in 200 year natural hazards event, e.g. earthquake etc. There are some dams however that have been designed to provide protection from events with even lower return periods.

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 down stream. Possible consequences of this are:

• flooding of land and communities located downstream of the dam with a consequent risk of loss of human and 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 kilometer 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
• emotional trauma.