Understand flood risk in your region

Northland can experience intense subtropical rain, short-notice river rises, surface flooding and coastal effects. Short, steep catchments can respond quickly, while low-lying floodplains and estuaries may hold water longer.

Auckland’s dense urban catchments can produce rapid surface flooding when intense rain exceeds pipe or inlet capacity. Overland flow paths, flood-prone depressions, streams and coastal inundation can all matter at property level. Major earthworks and development can change local topography, so use the latest available mapping and site observations together.

The region includes large river systems, the low-lying Hauraki Plains, steep Coromandel catchments and exposed coastlines. Flooding can involve rivers, local drainage, coastal water levels and long-duration catchment runoff. Waikato Regional Council’s Flood Room uses real-time rainfall, river levels, soil saturation and models, and manages assets including floodgates and pumps.

Major rivers and coastal lowlands mean river, drainage and coastal flooding can interact. The region’s river schemes include stopbanks, floodwalls, floodgates, pumps and drains. Heavy rain in steep upper catchments may take time to move downstream, so local weather alone does not tell the whole story.

Steep terrain, intense rainfall and fast-rising rivers can create short warning times. Flooding may be accompanied by slips, debris and road access problems. Gisborne District Council provides rainfall and river observations, river forecasts and camera feeds, but communications and cameras can be disrupted during severe weather.

Large rivers, alluvial plains, steep headwaters and smaller fast-response catchments create several kinds of flood risk. Stopbanks and drainage schemes provide important protection, while extreme events can still involve deep or fast water, erosion, debris and changing river channels.

Many Taranaki rivers are short and steep, draining from higher ground toward the coast. Orographic rain can produce rapid rises, and urban surface flooding can occur where local drainage is exceeded. Regional monitoring includes rainfall and river levels, with stations able to transmit more frequently during events.

The region contains large river systems, hill-country catchments and low-lying plains. Manawatū and Oroua river levels, smaller streams, urban drainage and coastal conditions can all affect local risk. Horizons manages numerous river and drainage schemes. The Moutoa floodgates can divert Manawatū River water through the floodway toward the sea, relieving pressure on the lower river. Near Feilding, the Makino floodgates are another visible part of the local flood-management system.

Flood risk varies from fast urban runoff and short coastal streams to major rivers such as Te Awa Kairangi/Hutt, Ōtaki, Waikanae and Ruamāhanga. Steep terrain, constrained valleys, high tides and stormwater capacity can combine. Some urban flood information is held by city or district councils rather than Greater Wellington.

Tasman includes wet western catchments, major rivers, low-lying floodplains and coastal areas. Heavy rain can affect the Aorere, Tākaka, Motueka, Waimea and other catchments, while slips and road isolation may accompany flooding. Council monitoring covers rainfall, river flow, groundwater and tides.

Nelson’s steep urban catchments can concentrate runoff quickly into streams and the Maitai/Mahitahi River, while low-lying areas can also be influenced by tide and stormwater capacity. Council operates near-real-time rainfall and flow monitoring across local freshwater management units.

The Wairau system, Ōpaoa and other rivers can respond to rainfall across large upstream catchments. Floodwater may affect floodways, fords, roads and low-lying land before urban areas. Marlborough’s Floodwatch combines rainfall, river flow, level data and local thresholds, with data refreshing automatically.

The West Coast is exposed to very high orographic rainfall. Short, steep rivers can rise rapidly, while the Buller/Kawatiri, Grey/Māwhera and other larger systems can produce widespread flooding. Coastal conditions, slips, debris and transport disruption may occur at the same time.

Canterbury’s flood risk includes large alpine-fed braided rivers, foothill catchments, low-lying plains, urban surface water and coastal drainage. Rain in alpine headwaters may be far from the property it later affects. Snowmelt contributes to seasonal flows, and warm rain on existing snow can add runoff in some catchments.

Otago combines alpine lakes and rivers, the Clutha/Mata-Au and Taieri systems, smaller steep catchments, and low-lying urban areas including South Dunedin. Flood drivers range from prolonged catchment rain to intense urban rain, high groundwater, tide and snowmelt contributions.

The Mataura, Ōreti, Aparima and Waiau systems drain large catchments into low-lying plains and estuaries. Heavy rain, saturated ground, local drainage constraints and, at times, snowmelt can combine. River levels may continue to rise after rain eases in the immediate area.