The dam break analysis of the proposed Ruataniwha Water Storage Scheme suggests half of Waipawa's 2000 population would be put at risk if the dam was to fail in an earthquake.
Failure of the main dam after construction, assuming the reservoir is full, would likely result in significant damage to infrastructure including bridges, roads, stopbanks and sewage treatment plants, and environmental damage to the river corridor and surrounding flood plain.
The resulting flood wave from a dam break would overtop the stopbanks at the town of Waipawa, and water depths in the area of Bibby Street near the Waipawa sewage treatment works would likely be in the order of two to four metres.
Due to the potential risks, along with the size of the main dam, the potential impact category of the main dam was classified as high, the report by the Hawke's Bay Regional Council said.
"Accordingly, the dam is designed to reflect this standard."
Hawke's Bay Regional Investment Company Limited managing director Andrew Newman said the dam break analysis was hypothetical and separate to the probability of a dam failure occurring.