Successful Performance of Detention Dams in the February 2004 Manawatu Floods
Author: Don R. Tate
Presented/Published: IPENZ Conference 2006
Keywords: Detention dam, Porewa, Tutaenui, Matarawa, Manawatu floods, February 2004.
Abstract:
The Manawatu floods of February 2004 were an extreme event, causing widespread damage over a wide area. The townships of Scotts Ferry and Tangimoana, located adjacent to the Rangitikei River, were inundated, as well as parts of Feilding.
Large areas of the Manawatu River flood plain were also flooded. A number of stopbank breaches associated with this flooding have been widely publicised. However, the successful performance of a large number of detention dams subjected to the same extreme event has not been recognised.
These dams total 53 in number and are owned by Horizons Regional Council. These dams fulfilled their design function of limiting flooding and, in particular, limited flooding in the towns of Hunterville and Marton and in Wanganui East. Most dams were subjected to the greatest flood event since their construction, and in most cases the spillways operated for the first time.
This paper describes the background of the dams, the flood event, and observations made of their performance, and describes the damage to a few dams. Risk areas for typical detention dam designs are then discussed, followed by historic management aspects of the Manawatu dams in the context of the pending dam safety legislation and possible impacts on their ongoing management.
