Leeston Stormwater Flood Bypass
Leeston Stormwater Flood Bypass Project
Leeston has always been prone to flooding, the Leeston creek is known to breach banks especially during high rainfall events causing the flooding issues in Leeston. Following the June 2013 flood event, a public meeting was held which the community asked the Council to look at options to divert flood waters from the farm land around the township and manage localised flooding within the township.
Following public consultation, a resident’s survey and the review of numerous options and design reports the decision for the bypass was approved by Council as the best option going forwards.
The bypass will redirect the main flow of floodwater away from the town centre for a 1% AEP storm event (1-100yr) through a specifically designed channel following the path indicated in the image below. This will restrict what goes through the centre of town while still keeping the base flow through the Leeston Creek protecting its ecological and biodiversity values.
The approval is for a multi-stage phased project which started with Stage 1 in 2014 and is expected to be completed around 2026.
Stage 1 Completed 2014/2015 by Grant Hood Contracting. Stage 1 was the connection of the Ellesmere Hospital drain to Manse Road and widening of the High St Drain. | Stage 2 Completed 2016 by Johnston Civil Ltd. Stage 2 was the upgrade of the Manse Road Drain and Reids Culverts |
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Stage 3 Completed December 2020 by Sicon / Blakely Construction
Stage 3 involved the replacement of High St culverts and connection of these into Volckman Rd Drain. This will increase the flow capacity to 8.1 m3 per second (from 4.3m3 per second). Existing Culverts were replaced with two parallel box culverts sized 2.5 m x 1 m and the base width of the drain immediately downstream has been increased to enable the bypass to operate effectively.
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Stage 6 Completed as part of the Karumata Oaks subdivision.
Stage 6 involved the creation of a wetland to service the new area of development from Pound Rd / Leeston Dunsandel Rd.
Stages 4 and 5 Work is planned to commence 2024/2025.
Stage 4 includes the Leeston Creek Diversion structure and the diversion channel which will protect Leeston Township from flood events. This stage also includes targeted improvements of the drainage network downstream of the township to minimise any adverse impacts on landowners.
Stage 5 includes widening and deepening of the Leeston Creek channel between Harmans Rd and the bypass diversion, as well as any targeted improvements to the drainage network upstream required.This shall provide additional capacity for high flows and minimise the chance of upstream breakouts which could affect the township.
Council is currently finalising land access arrangements with landowners and completing design and consenting details to allow construction
These stages are more fully described in the resource consent application and its supporting appendices, available here.