How we manage and reduce flood risk

Environment Southland owns and maintains more than 500 kilometres of flood banks and other assets that help reduce the effects of flooding on people, property, livelihoods and critical infrastructure.

Our flood-infrastructure network includes:

• flood banks and earthworks
• detention dams
• bridges
• large culverts
• tide gates

Flooding is an ever-present risk in Murihiku Southland. We run a long-term programme to maintain and improve the flood infrastructure network. Our integrated catchment approach brings together data and modelling, land-use planning, nature-based measures and traditional infrastructure. The aim is to reduce flood impacts, keep key routes and essential services operating, and shorten recovery after major rainfall or coastal events.

Learn more about how this fits within the region-wide Flood Resilience Programme.

Data and modelling

Understanding how rivers, streams, and floodplains behave is central to managing flood risk. Environment Southland uses flood modelling to assess how rainfall, land-use changes and climate change affect river systems.

These models inform the design and sequencing of flood infrastructure works, guide planning decisions and help identify areas most at risk during extreme rainfall.

Learn more about Flood Modelling in Southland.

Maps

Southland Natural Hazards Portal (address-level hazard information)

Use the portal to search for an address and view flooding, historic flood photos, coastal hazards (e.g., tsunamis) and selected earthquake-related layers. You can also request a specific comment from Environment Southland via the portal if more detail is needed.

Flood Infrastructure Map (network and operations)

This viewer shows the flood-infrastructure network and operational layers — including alerts, flood banks, dams and drainage networks — across the region. It’s useful for understanding where assets are and current conditions, rather than for property-level hazard assessment.

National flood tool

Earth Sciences New Zealand (formerly NIWA) has released the National Flood Tool. The tool provides a consistent overview of where flooding from 1% AEP (one-in-100-year) rainfall could occur under the current climate and with +1, +2 and +3 °C of additional warming. It is zoomable to street level (not property level) and links users to regional or unitary council flood maps where available.

The National Flood Tool is designed for national-scale screening and awareness, not for property-by-property assessment or consenting decisions.

Learn more and access the viewer on Earth Sciences New Zealand’s website.

What happens when rivers rise?

Environment Southland's role

We monitor river levels and flows across the region. When water levels reach key trigger points after heavy rain or snowmelt, we issue flood alerts so people can take precautions. See our Flood warning page for current alerts and how to receive notifications.

Emergency Management Southland's role

If flooding may threaten life or property, Emergency Management Southland leads the emergency response on behalf of the four southern councils.

Follow EMS for official updates and verified information during declared emergencies.

A quick note on flood banks

During the February 2020 event, our teams used local knowledge, monitoring and models to support on-the-ground decisions. In many locations, the flood banks performed as designed, helping to reduce flood impacts on nearby towns.

Read the full Envirosouth story here.

How this work is funded

Our flood-risk-reduction work is funded through the Flood Infrastructure Investment Rate (introduced in 2025) and national co-funding such as the Kānoa-MBIE Regional Infrastructure Fund (RIF).

The new rate replaces multiple historic river-scheme charges with a single region-wide approach, providing sustainable funding for maintenance, renewals and improvements to the flood infrastructure network. This enables us to maintain agreed service levels, reduce the effects of flooding and plan long-term upgrades.

Documents

• Southland Flood Control and Drainage Management Bylaw 2020 – protects the integrity and safe operation of flood banks, detention dams, bridges, culverts and tide gates. It manages activities near these assets to ensure they continue to function effectively during floods.
• Infrastructure Strategy 2021–2051 – outlines how Environment Southland manages, maintains, and plans for the renewal of key flood-infrastructure assets. It identifies future challenges such as climate change, asset condition, and funding needs, and sets a long-term approach for sustaining agreed service levels and reducing flood risk.

Videos

View drone footage of the Wāihopai River after heavy rainfall in October 2020. The flood banks and the dam are doing their job, holding back the floodwater and letting it through slowly.

View a short flood bank and seepage video from Bay of Plenty Regional Council, which explains how flood banks are constructed, how they work and why maintaining their integrity is crucial.

Below is a video from 1984 about the devastating floods that struck Invercargill and western Southland.