Managing flood risk in the current District Plan
The current Selwyn District Plan identifies and manages the following rural flood areas:
- Waimakariri Flood Category A Area
- Waihora/Lake Ellesmere Flood Area
- Lower Plains Flood Area.
Within these rural areas the use, development and subdivision of land is restricted through consent requirements including:
- site-specific assessment of natural hazard risk;
- minimum floor levels for new dwellings and other principal buildings (eg commercial buildings); and
- controls on earthworks.
Within townships, only Tai Tapu and Rakaia Huts are currently subject to flooding controls. In Tai Tapu, new dwellings and principal buildings are subject to minimum floor heights, while new dwellings or principal buildings on the lower terrace at Rakaia Huts are automatically a non-complying activity. This means that a resource consent would be required and would be difficult to get.
Key issues with the current District Plan
The key issue with the current District Plan is that the flood maps are based on information that is now over 20 years old and in several instances relies on information dating back to the 1970s. Also, the maps identify only areas known to have flooded in the past and areas at risk of flooding during a one-in-50-year flood event.
In the new Proposed District Plan we are required to identify and manage areas at risk from more extreme events: a one-in-200-year or a one-in-500-year flood. When identifying areas that could be susceptible to flooding, we also need to account for climate change effects over the next 100 years, such as increased frequency and intensity of rainstorms.