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Lower Wairarapa Valley Development Scheme

http://www.gw.govt.nz/lower-wairarapa-valley-development-scheme

Lower Wairarapa Valley Development Scheme

Updated 11 March 2020 4:32pm

The Lower Wairarapa Valley Development Scheme is one of New Zealand's largest and most ambitious flood protection projects, benefiting a total land area of 41,00 hectares. Greater Wellington is responsible for the implementation and maintenance of the Lower Wairarapa Valley Scheme.

It covers the section of the Ruamahanga River from the Waiohine confluence downstream to the Lake Onoke outlet into Palliser Bay, the Tauherenikau River from the rail bridge downstream to Lake Wairarapa, and all the eastern and western tributary streams.

The Ruamahanga River was diverted from its direct course into Lake Wairarapa, across the Kumenga Peninsula and into the Lower Ruamahanga. The barrage control gates largely prevent all normal flows of the Ruamahanga from entering Lake Wairarapa.

The barrage has also enabled levels of Lake Onoke to be raised quickly to either overcome impending blockage of the outlet or to aid in the formation of a new opening. This also means that the lake can be kept at a low level, ready to accept any flows from the Oporua Floodway. Such flows are the result of the overflow of flood discharges from the Ruamahanga River at various points further upstream. Flow size is dependent on the size of the flood event and can not be controlled.

The ability to be able to maintain an efficient and ever-lasting outlet from Lake Onoke to the sea has been of great worth since it is the key to preventing flooding in the Lower Wairarapa Valley. Subsequently, the scheme has produced much of the expected benefit. The flood protection works were tested in the major floods of 2004 and they held up well despite the extreme conditions.  

The land-use patterns and environment of the Lower Wairarapa Valley are now well-established. Our aim is to allow for improvements in the quality and security of this environment. If you have assets or an interest in the area, you may want more information about the scheme (please contact the Greater Wellington's Masterton office on 06 378 2484.

Greater Wellington has more information about the scheme and the floodplain, the risk of flooding, and what has been done to minimise its impact. We are also responsible for how the scheme will be managed in the future.

Key Facts

  • Construction started in 1963 and was completed in 1983
  • Flood protection standard is 20-year frequency in upper reaches, and 100-year frequency in lower reaches
  • Present day asset value is $160 million; annual maintenance budget including river and drainage scheme operations is $1.5 million, with a capital development programme of around $1.0 million
  • Increase in annual production generated by the Scheme is $100  million
  • The Ruamahanga River channel length included in the scheme is 65 km
  • Total length of stopbanks is 190 km
  • Includes 112 culverts and floodgates, a total of 12 drainage schemes and 190 kilometres of stopbanks
  • The six pump drainage schemes service 3550 hectares and have a total flow capacity of 7.1 cubic metres per second