Halswell River landowner assistance sought to reduce flood risk

Environment Canterbury engineers are working with landowners and the community in the Halswell River rating district to repair the river system damaged during the September 4 earthquake.

Chief executive Dr Bryan Jenkins said co-operation from land owners was essential for work to be undertaken as efficiently as possible.

“It will be a considerable time before the river system achieves long term stability. To start getting back to how it was, we need to have access to the river and we need to avoid delays which will increase costs to ratepayers.”

The flood risk in the catchment has increased because of four changes resulting from the earthquake. Firstly groundwater tables have risen. Secondly sediment from sand “boils” has accumulated in the riverbed reducing the channel’s capacity. Thirdly lateral spread from liquefaction has reduced the width of the drainage channels due to banks collapsing on either side. Fourthly, there has been land subsiding.”

Dr Jenkins said Environment Canterbury is gathering information to understand the changes to the Halswell River’s drainage system. Engineers plan to discuss longer term remediation options with the rating district’s liaison committee at a meeting planned for November.

“Funding may be available from the Ministry of Civil Defence Emergency Management. However residents living in the district may be asked to consider rate increases to restore the scheme’s capacity, to continue farming and land use activities, and reduce the risk of high groundwater levels or flooding in the future.

“Environment Canterbury will also be liaising with other areas to address whether their land and waterways require repair work and how they can be adequately protected in the event of another emergency. There will be variations in the rating levels across the districts, related to their levels of reserves and earthquake damage.”