River flooding

Flooding in the Waikato region

River flooding is a frequent event in the Waikato region

• The region is susceptible to storms of tropical origin.
• Our many steep river catchments get intense, localised rainfall that is also difficult to predict.
• The region has large river systems, as well as large areas of low-lying flood plains near sea-level that are intensely farmed or developed.
• We have large areas of land  that lack vegetation cover. This increases run-off and erosion.

River flooding is more likely to occur when:

• heavy rain runs off already saturated soils
• a river channel is no longer able to hold the volume of water
• damaged or poorly constructed stop banks fail to hold floodwaters back
• drains (such as storm water drains) are blocked by debris
• there is a high tide or king tide, increasing water levels in rivers that flow into the sea.

Climate change increases the risk

As a result of the projected effects of climate change, more heavy rainfall will increase the risk of inland flooding in the west and in river catchments in the Coromandel.  Increased sea levels (due to sea level rise) will also increase the risk of river flooding in rivers that are influenced by sea level, such as those that drain to the sea.

• Coromandel - due to its short steep catchments (where rain quickly runs into the rivers) and susceptibility to tropical storms. The Coromandel has frequent severe flooding when water levels rise very quickly, with little time for warning and preparation.

• Hauraki Plains - low lying farmland and towns are vulnerable to flooding along the Waihou and Piako river systems. 

• Farmland adjacent to the Waipa River – vulnerable to flooding, especially since the river is uncontrolled by dams.

• Lower Waikato River (from Ngaruawahia north) - properties on low lying land near the Waikato River are at risk. The River carries large volumes of water where the Waipa River joins the Waikato River.

• Flooding at the southern end of Lake Taupo - where the Tongariro and Tauranga-Taupo rivers enter the Lake.

Waikato Regional Council has responsibilities for managing flood risk in the Waikato region.

Our automated recorder sites constantly check on river levels and rainfall around the region. We track river levels to see how quickly rivers are rising during storms, and we have flood warning systems in place to help us manage floods to protect people and their property. We also keep an eye on how much rain is falling at sites around the region, to help us predict river levels and estimate how much more water the land can soak up before it runs off into rivers.

Our other roles and work to avoid or reduce the impact of flooding include:

• Education of stakeholders, including the public.
• Sensible planning by locating development away from flood pathways.
• Stopbanks - which keep water within the channel.
• Control structures - such as flood gates, which divert water to be held until it can be released when water levels fall and pumps which pump ponded water back over the stopbanks.
• Dams on the Waikato River - which allow flood peaks to be held back so they don’t coincide with the Waipā River peak flow where the two rivers join at Ngaruawahia.
• Catchment management - through planting, soil conservation and pest control. 
• Land drainage - which helps keep the water table low.