|The barage gates||The Ruamahanga River diversion|
The LWVD Scheme is a flood protection scheme for the Lower Wairarapa Valley.
It starts about 2 kilometres downstream of the Waiohine and Ruamahanga confluence to where Lake Onoke enters Palliser Bay and covers the valley between the western ranges and the eastern hills. It includes the Tauherenikau River and all the tributary rivers that flow into Lake Wairarapa and Ruamahanga River.
The stopbanks and natural high land protect the area for a 20-year plus flood event. It is interesting to note that the system largely coped with the 50 year flood event in 2004.
A works programme for the operation and maintenance of the scheme is managed by the Flood Protection Department of Greater Wellington Regional Council.
The Scheme has an Advisory Committee who provide advice on operations and liaise between landowners and Flood Protection staff. The programme involves work such as planting and vegetation control, stop bank maintenance and upgrades, fences, floodgates and channel work (alignment and bank protection), operation of the Barrage Gates and physical opening of the river mouth to the sea when it gets blocked.
There are several natural and man-made features that are used to provide flood protection to the area:
There are four main scenarios under which the Barrage Gates operate:
Lake Onoke is open to the sea. The gates are operated to achieve the Target Levels specified in the Resource Consent.
The barrage gates are closed and the water level is allowed to rise until it is at a maximum allowable level. When this level is reached, a cut is put into the bank of Onoke Spit. However, the Spit can’t be opened if the sea is rough in which case the gates are opened to backflow excess water into Lake Wairarapa. Once the Spit is open and the river level has dropped, the gates are opened to let the excess water out.
The gates are closed to stop Lake Wairarapa filling up. The Spit is open so water goes out to sea.
When the river peak has gone the Gates are opened to let the excess water out.
There is a flood warning system in place for the landowners in flood-prone areas. They are alerted to manage stock and prepare for a flood.
In the past, large amounts of silt would have been deposited in the lake during floods; the silt would have been blown off during summer when the natural lake level would have been very low to form sandhills on the eastern side. Bulk of the silt is now carried to the sea during flood events.
The Flood Protection Scheme is funded 50:50 by benefiting landowners and general ratepayers.
Greater Wellington Regional Council is responsible for the management of the LWVD Scheme and more information can be found about the history and the Scheme on the GWRC website.
Content on this page was last updated: 14/02/2017 11:12am