Rangitaiki River: A History of Land Drainage and Power Generation
The Rangitaiki River has undergone significant transformations over the last century, evolving from a natural wetland system into a highly managed landscape of productive farmland and renewable energy hubs. Through legislative action and engineering feats, the region has been reshaped to support agriculture and provide electricity to the surrounding areas.
The Transformation of the Rangitaiki Plains
Following the arrival of Europeans, extensive efforts were made to drain wetlands and low-lying areas along the river to create viable land for horticulture and agriculture. This movement was formalized by the Rangitaiki Land Drainage Act 1910, which facilitated the conversion of approximately 40,000 hectares of wetland into farmland.
A pivotal change occurred in May 1914 when a new channel was cut near Thornton. Previously, the river had dual discharges flowing toward the Whakatāne River to the east and the Tarawera River estuary to the west. The new direct outlet to the sea caused the river level in the lower Rangitaiki Plains to drop by roughly 1.5 metres (4.9 ft) within a single day. This dramatic shift encouraged further agricultural expansion after World War I.
[ไม่มีภาพประกอบ]Flood Control and Mitigation
To protect productive land and human settlements, various flood mitigation schemes were implemented under the Land Drainage Act 1908, the Soil Conservation and Rivers Control Act 1941, and specific legislation including the Rangitaiki Land Drainage Acts of 1910 and 1956.
Downstream of Te Teko, the landscape is protected by stopbanks (also known as floodbanks). These engineered barriers are designed to withstand a 1% Annual Exceedance Probability (AEP) flood, commonly referred to as a "100 year" flood, ensuring that the surrounding community remains secure during extreme weather events.
Hydro-Electric Development
The latter half of the 20th century saw the Rangitaiki River become a source of renewable energy through the construction of three hydro-electric schemes. All three operate as run of the river schemes, meaning they have limited storage capacity and rely on the natural flow of the river.
Matahina Power Station
Commissioned in 1967, this station features the 86 m (282 ft) high Matahina Dam, which created Lake Matahina. The facility is capable of generating up to 80 MW of power.
Wheao and Flaxy Power Scheme
Commissioned in 1980 and located within the Kaingaroa Forest, this scheme diverts water from the Rangitaiki and Wheao rivers, as well as Flaxy Creek. It powers two stations: the 24 MW Wheao Power Station and the 2.1 MW Flaxy Power Station.
Aniwhenua Power Station
Commissioned in 1981 above the Āniwaniwa Falls, this station uses a 10 m (33 ft) high dam at the confluence of the Rangitaiki River and Pokairoa Stream. This created Lake Āniwaniwa (unofficially Lake Aniwhenua), which supports a regionally significant trout fishery and various recreational activities. The station generates up to 25 MW.
[ไม่มีภาพประกอบ]Recent Challenges: The 2017 Flooding
Despite extensive flood control measures, the region faced a severe crisis in April 2017 due to remnants of Cyclone Debbie. On April 6, at 8:30 am, the Rangitaiki River breached the College Road floodwall at Edgecumbe, leading to widespread flooding throughout the township.
The event triggered a state of emergency for the Whakatane District, resulting in the evacuation of approximately 2,000 people to Kawerau and Whakatāne. More than 300 homes were damaged, with some rendered uninhabitable. A formal review of the disaster was subsequently conducted by a panel chaired by Sir Michael Cullen, alongside Kyle Christensen and Charlie Price.
Key Facts
- Wetland Conversion: Approximately 40,000 hectares were drained for farming.
- River Level Drop: The 1914 Thornton outlet caused a 1.5-metre drop in river levels.
- Flood Protection: Stopbanks are designed for a 1% Annual Exceedance Probability (AEP) event.
- Energy Capacity: Three run-of-the-river schemes provide power, with the Matahina station being the largest at 80 MW.
- 2017 Impact: Cyclone Debbie caused a breach at Edgecumbe, damaging over 300 homes.
| Power Station | Commissioned | Capacity | Key Feature |
|---|---|---|---|
| Matahina | 1967 | 80 MW | 86m high dam / Lake Matahina |
| Wheao & Flaxy | 1980 | 26.1 MW (Combined) | Located in Kaingaroa Forest |
| Aniwhenua | 1981 | 25 MW | Lake Āniwaniwa / Trout fishery |
Frequently Asked Questions
What is a run of the river scheme?
A run of the river scheme is a type of hydroelectric generation where the facility has limited water storage capacity, relying on the natural flow and current of the river to generate electricity rather than a large reservoir.
How did the 1914 channel cut affect the region?
The cutting of a channel near Thornton provided a direct outlet to the sea, which lowered the river level in the lower Rangitaiki Plains by about 1.5 metres, making the land more suitable for agricultural and horticultural development.
What is a 1% Annual Exceedance Probability (AEP) flood?
A 1% AEP flood, often called a "100 year flood," is a flood event that has a 1% chance of being equaled or exceeded in any given year.
What happened during the Edgecumbe flood of 2017?
Heavy rainfall from Cyclone Debbie caused the Rangitaiki River to breach the College Road floodwall, leading to the evacuation of 2,000 people and damage to over 300 homes.
Which hydro-electric station has the highest capacity?
The Matahina Power Station has the highest capacity of the three schemes, capable of generating up to 80 MW.