Nelson, like any city in New Zealand, is subject to hazards that we need to manage. One of those hazards is slope instability which is reflective of the varied geology of the city.
One of the areas that are affected by instability is the Tahunanui slump - a 26-hectare area of hillside overlooking Tahunanui Beach.
Council has a project to work on improving the stormwater management of this area, to potentially reduce the chance of a weather event causing issues in this area.
There are three parts to this overall project, Catchment 3, Catchment 4 and Catchment 9. There are 9 catchments identified in the Tahunanui slump area.
The upgrade of the stormwater network in Catchment 3 of the Tahunanui Slump (TS) aims to reduce the geotechnical risk in the area - both to the stormwater services and from those services. It will also aim to reduce the risk of surface flooding.
Compared with other catchments within the Tahunanui Slump, Catchment 3 is the most at risk from poor stormwater control.
It has historically had the highest degree of ground movements, and the piped stormwater network is particularly vulnerable to future movement.
The consequence of this movement has the potential damage to public and privately built infrastructure.
Council has been carrying out a multi-stage study of the risk to and from the public stormwater system within the Tahunanui slump.
Ground movement in the slump has the ability to damage below-ground infrastructure such as concrete pipes. The Tahunanui Catchment 4 stormwater upgrade project is a multi-year project. It is a key project for this Council that will improve the stormwater management in the Tahunanui hills.
An opportunity has arisen on private land that will allow Council to upgrade the stormwater pipe in this area.
The stormwater project in Catchment 9 of the Tahunanui Slump (TS) aims to reduce the geotechnical risk to, and from, stormwater services. It will also aim to reduce the risk of surface flooding.
Compared with other catchments within the TS, Catchment 9 is the biggest one.
Stormwater overflow from the current system may infiltrate into the ground at the boundaries of slump blocks. This has the potential to contribute to block movement. The consequence of this movement is potential damage to public and privately built infrastructure.