If repairs are needed, you should check with your local council to see if consent is needed before you carry out the work.  Councils also have emergency powers under the Resource Management Act to carry out work if immediate preventive or remedial action is required.
In the case of an extreme weather event, some preventative or remedial work is possible on rural land without council consent. There are some limitations on these works, which include that they don’t cause significant adverse effects beyond the boundaries of the land. You’ll still need to get retrospective consent from the council within a certain time period.
Public roads