Flood hazard modelling

Flood hazard modelling is an important tool for predicting the likely impact of extreme rainfall, runoff, and flooding risks. It involves the use of hydrologic and hydraulic models to estimate the range of possible floods that could occur in a catchment and the hazards associated with these events.

How flood hazard models work

The first step in flood modelling is to analyse rainfall patterns. These models are then combined with information from previous events to help determine where flood waters might go in the future.

We use these models to:

• produce flood hazard maps.
• plan improvements to our stormwater network.
• develop flood management policies, such as those in our District Plan.
• prioritise investment for growth planning.
• minimise flooding impacts on our community.

Local flood hazard models 

Flood hazard models are essential for identifying areas at risk and guiding infrastructure improvements to reduce flood impacts.

• Our Council’s models address flooding associated with local drainage and stormwater networks, as well as local streams.  
• We’re revising our models to include the Te Kowhai and Muaupoko catchments, and the latest environmental climate change predictions, groundwater modelling, recent housing developments, and major infrastructure projects such as stormwater network upgrades and major roading projects such as Transmission Gully to provide a more accurate understanding of flood risks within our urban drainage network.   

Our current flood hazard maps can be found here.  

Major river flood hazard models  

These models are vital for understanding the risks posed by large river systems and their potential impact on surrounding areas.

• Major river flooding is the responsibility of Greater Welington Region Council (GW). In Kāpiti, these models include the Waikanae River, Ōtaki River, and Mangaone Stream and their associated waterways.   
• Major river flooding can impact parts of the district not affected by flooding associated with the stormwater network and local streams.  

 Read more about Greater Wellington’s current hazard maps.

Greater Wellington is updating their flood hazard maps for Kāpiti Coast rivers and streams. You can be involved in this process.  

The National Institute of Water and Atmospheric Research (NIWA) models 

NIWA is undertaking a nation-wide flood hazard mapping project, with preliminary outputs expected in mid-2025.  Although the mapping produced by NIWA will not be as accurate as councils’ local models, it will inform Government responses to emergency management and other related policy reform.