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Submissions open for Motueka flood control options

April 13th, 2011
[based on TDC press release]

Tasman District Council is investigating improving the flood control measures for the Lower Motueka River near Motueka township and Riwaka. After an initial round of community consultation and investigation five options have been identified for further consideration.

Members of the public are invited to have their say about their preferred option. Council has prepared some web pages with comprehensive background and information about the process so far, along with a facility to make submissions and "vote" for their preferred option online. View that information here »

Council says there are some options which seem preferable and will be subject to further consideration. These can be summarised as (in no particular order):

* Option A)  Status quo use the existing stopbanks only
* Option B)  Build secondary stopbanks (left bank only or right bank only)
* Option C)  Build spillway(s) at selected location(s)
* Option D)  Refurbish (improve) existing stopbanks
* Option E)  Rebuild (new) stopbanks.

The Council website includes diagrams to illustrate each of these options. Generic elements common to all options could include:

* Ongoing removal of debris and illegally dumped materials from river flood path
* Continued removal of Crack Willow which tends to break in a storm event
* Monitoring and redistribution of gravels within the river berms
* Inspection and rectification of damage caused to rock wall and stopbank footings by erosion and or human activity
* Improved river maintenance
* Improve channels around Peach Island.

Council considers that these last ideas should be considered as part of any future flood mitigation strategy.

An initial system of stopbanks was constructed around the Motueka River between 1951 and 1956. The original construction was designed to withstand a 1 in 50 year of flood with 600mm of the stopbanks still above water.

Significant floods were recorded in the Lower Motueka Valley in 1957, 1974, 1983 and 1990. The 1983 flood was recorded as a 1 in 69 year flood and came within 200mm of the top of the stopbanks in some locations. The 1957 flood is thought to have been larger than the 1983 event with one reported stopbank failure.

In 2008 the Motueka Flood Control Project was started to increase the flood protection to withstand a 1 in 100 year flood, while taking into account modern river flow information and the projected effects of climate change (sea level rise and more extreme weather).

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