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The Waikato region has 20 large rivers and many small river systems. Flooding is frequent because of steep terrain, low lying flood plains and areas of high rainfall. Find out more about river flooding and how it is managed in the Waikato region.
A lot of the region's 20 large and 1,420 small river systems are prone to flooding. Many people remember extensive flooding in the Waikato region in 1958. More recently, back-to-back storms in July 1998 caused widespread flooding.
River flooding can threaten people’s lives and property and damage our environment. ‘Lifeline’ services such as water, power, telecommunication and transportation networks can also be damaged. Find out more about managing lifelines to deal with unexpected emergency or natural hazard events.
Environment Waikato has developed a strategy for river flood risk management which will assist all stakeholders (including district and regional councils) to integrate their respective responsibilities under different pieces of legislation.
Flooding in our region
River flooding is a risk in the Waikato region because:
- it is susceptible to tropical storms
- many steep river catchments get intense, localised rainfall that is difficult to predict
- it has large river systems
- it has large areas of low-lying flood plains near sea-level that are intensely farmed
- large areas of land lack vegetation cover, increasing runoff and erosion.
Controlling floods
Flooding can be controlled using:
- Control structures - such as flood gates, which divert water to be held until it can be released when water levels fall.
- Stopbanks - which keep water within the channel.
- Dams on the Waikato River - which allow flood peaks to be held back so they don’t coincide with the Waipa River peak flow where the two rivers join at Ngaruawahia.
- Catchment management - through soil conservation and pest control. Uncontrolled pests can damage vegetation, increasing the chance of soil erosion and flash flooding. Adequate vegetation cover stabilises the ground and absorbs water, controlling water and sediment running off sloping land.
- Land drainage - which helps keep the water table low.
Risk factors
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.
High tides can also affect river flooding, increasing water levels in a river where it flows into the sea.
Risk areas
- 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. Click here to find out more.
- 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.
The costs of flood control mean it is more appropriate to avoid development in at-risk areas.
What we are doing
- Environment Waikato prepares and implements risk mitigation plans, such as site-specific risk mitigation strategies for high-risk areas. These include our:
- We operate a flood warning system as part of our emergency response.
- We are involved in managing three major flood protection schemes on the Waihou, Piako and Lower Waikato rivers, as well as numerous drainage schemes. We also manage smaller scale flood protection river management and soil conservation works throughout the Waikato region.
- We provide information to increase people's understanding of flooding and related issues.
- We are involved in developing a river and catchment management plan for the Thames Coast. This project will look at river management, flood protection, soil conservation and the development of the Thames Coast River Flood Hazard Study.
- We are involved in assessing the erosion and flood hazards around Lake Taupo's foreshore
- We are currently developing a regional flood risk mitigation strategy which will define roles and responsibilities for stakeholders, outline decision making policies and guidelines, and set the requirements for flood related information.
For policy information on how Environment Waikato manages flood risk, check out the Regional Policy Statement.
Environment Waikato’s flood warning system
Environment Waikato operates a flood warning system, with staff dealing with system alerts activated by heavy rainfall and rising river levels. Environment Waikato uses the system to:
- monitor River Levels and Rainfall at over 50 automated recording sites
- warn landowners and communities about a flood
- collect data to improve our accuracy of flood prediction
- co-ordinate flood response
- maintain flood protection works, such as stopbanks, in low lying catchments.
Early warning: flood level and rainfall
When river levels at a site reach a set level or rain is very heavy, our early warning system is activated.
The early warning flood level indicates that a river’s level should be more closely watched. Our 0832 Infolines service provides telephone information about the various sites we monitor. This information varies between sites but can include:
- river level
- rainfall
- barometric pressure
- wind speed
- wind direction
- air temperature
- river flow.
River Flood Risk Management Strategy
River flooding is a significant hazard, being the most widespread and frequently occurring hazard within the Waikato region. Over time, many river systems within the region have been modified for the purposes of flood protection. River modification has:
- led to increased use of land in flood prone areas for both rural and urban purposes
- reduced flood hazard risks to both rural and urban areas
- greatly increased the economic productivity of land in flood prone areas.
While river modification has produced many benefits, it has not eliminated flood risks, and in some cases has encouraged the intensification of urban development within flood prone areas. River modification can also have significant adverse effects on natural river system characteristics, by altering the way in which rivers and flood plains would normally operate.
In recent years, issues such as population growth, land use change and the ever-increasing location of development within flood plains have compounded the risks associated with flooding. In addition, the frequency and intensity of extreme flood events appears to be increasing over time. This means that the provision of hazard information, land use policies and regulations, river and catchment management and related activities all need to be understood within the context of managing flood risks within a whole catchment.
As a result of the 2004 floods in the Manawatu-Wanganui and Bay of Plenty regions, the Government has recognised the importance of flood risk management to New Zealand. A significant amount of work has been completed by the Government, Local Government New Zealand and other key stakeholders to confirm national directions for flood risk management. As a result of this, national directions have become much clearer since 2004.
In order to achieve a reduction in the risks from flooding, all stakeholders, including district and regional councils, need to integrate their respective responsibilities under different pieces of legislation. This strategy intends to assist in this process. Download the strategy in PDF format below.
River Flood Risk Management Strategy
(473 kb, 67 seconds to download, 56k modem)
Thames-Coromandel river flooding
The Thames Coast Project is just one part of Environment Waikato's wider Peninsula Project. The Peninsula Project aims to deal with soil erosion, river management and flooding management issues throughout the Thames Coromandel District.
You can check out the following Thames Coast Project information in PDF format:
Find out more about
river and catchment management in the Waikato region.
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