Floods

The Region’s rivers begin their journey to the sea from steep, hilly and mountainous country.  Fed by high rainfall and storms, they flow rapidly and powerfully, carrying rock and other debris.  In these higher areas, much of the land is tree covered, which helps control the rate of run-off  from the land into the river channel.

Nearer the sea, rivers move more slowly, depositing their load of rock, shingle and sand.  These areas are called floodplains, natural features where floodwaters go when the river channel cannot cope with the amount of water. On an undeveloped floodplain, floodwaters seep into the ground, and swamps and wetlands help reduce the amount of extra water that needs to run-off downstream.

The Region’s rivers begin their journey to the sea from steep, hilly and mountainous country.  Fed by high rainfall and storms, they flow rapidly and powerfully, carrying rock and other debris.  In these higher areas, much of the land is tree covered, which helps control the rate of run-off  from the land into the river channel.

Nearer the sea, rivers move more slowly, depositing their load of rock, shingle and sand.  These areas are called floodplains, natural features where floodwaters go when the river channel cannot cope with the amount of water. On an undeveloped floodplain, floodwaters seep into the ground, and swamps and wetlands help reduce the amount of extra water that needs to run downstream.

Humans cause a flood hazard when they modify and develop the landscape, both by clearing forests and building on floodplains. Along with development comes more hard surfaces such as roads and buildings.  Water runs off  these hard surfaces quickly, and torrential rain in urban areas can overwhelm stormwater drains.  The combination of modified floodplains and heavy rain means the river cannot cope with the extra demand. Water flows onto the floodplain, and stormwater is unable to drain away. 

All floods can be dangerous to people and property, from the stream that runs past your house, to a big river that has many homes and businesses built alongside it (such as the Hutt  River).  Fast flowing water from even smaller floods can knock people off  their feet, move vehicles and damage bridges, phone and power lines, homes and other buildings. All floodwaters carry debris (such as parts of trees or wood from structures) that can cause further damage and hurt people. This is why you should not wade through floodwaters. Remember that even deeper, slow-moving water or ponding can be equally as dangerous. A large flood could break through or overtop stopbanks on any of our major floodplains, and cover extensive areas in water.

Flooding can affect essential services such as electricity, telecommunications, water supply and sewerage for days, if not weeks. A large flood could be more destructive than we have ever experienced before and the cost of a flood on a highly developed floodplain could exceed $1billion. Many people will be affected, causing a lot of stress and trauma. Communities are likely to be uprooted with hundreds possibly having to leave their homes. Many businesses would be out of action and schools may be forced to temporarily close.