Our places: Coleridge Habitat Enhancement Trust
Pūteketeke Australasian crested grebe image: Steve Attwood
Fig. 1 Lake Coleridge, Lake Selfe, Rakaia, Wilberforce, and Harper Rivers. Some water is diverted from the Harper and Wilberforce Rivers into Lake Coleridge in order to maintain hydro-electricity generation. The Coleridge Habitat Enhancement Trust is involved in habitat protection and enhancement work in the area shown in this photo and extending up into the Korowai/Torlesse Tussocklands Park and around Lake Lyndon. (Image: Googe Earth).
Context, origins, and purpose of the Trust
Lake Coleridge Whakamatau, formed around 20,000 years ago when glaciers retreated from mountain valleys at the end of the Pleistocene glacial epoch, leaving behind a complex system of braided rivers, lakes, tarns, and wetlands.
The Lake Coleridge Hydro Electric Power Scheme (Lake Coleridge HEPS) was opened in 1914 and purchased by Trustpower in 1998. The power station operates by diverting water from the Wilberforce and Harper Rivers, and the Acheron Stream, into Lake Coleridge for storage. The storage and use of water for power generation causes lake level fluctuations.
Just prior to Trustpower purchasing the HEPS, the resource consents authorising the operation of the Scheme were renewed. As part of this process, the Coleridge Habitat Enhancement Trust (CHET) was formed to administer an environmental enhancement fund to mitigate some environmental effects that could not be anticipated or provided for during the consenting process. This money is available to put towards environmental projects that ensure freshwater habitats (braided rivers, lakes, and wetlands) are maintained, enhanced, or created, and high country grasslands and shrublands are protected and continues to provides habitat for Aotearoa’s unique wildlife.
Key Actions
The Trust has representatives on it from Selwyn District Council, the Department of Conservation, Forest & Bird, Fish & Game, Trustpower and a local landowner representative. It has worked with other agencies including Land Information New Zealand, Environment Canterbury and BRaid on a number of projects:
- Removing weeds across sections of braided river braidplains and around lakes and wetlands. For example, wilding pines and willows are two species needing targeted control. Not all willows are removed as grebes/kamana and tuna/eels and other native freshwater species need shade and shelter along stretches of waterways.
- Trapping predators, particularly around riverbed areas where braided river birds nest and to help protect Australasian Crested Grebe nesting areas.
- Installing signs and improving visitor facilities that help protect vulnerable habitats (Figs. 3, 4 & 5).
- Organising and supporting surveys of threatened species including Australasian crested grebes, insects, and braided river birds.
- Engaging with the community, including local schools, in helping to spread the word about native ecosystems (Figs. 6, 7 & 8).
- Helping to coordinate the efforts of various organisations that have responsibilities in the area by sharing information about what work is happening and what’s required.
How this helps mitigate and adapt to the impacts of climate change
- Heavy bursts of rainfall over the mountains will intensify as the climate changes. This means that more water will fill the braidplains more often. In places where weeds (including wilding pines and willows) have spread across the braidplain, the braids of the river are forced into increasingly narrower channels. Rather than the energy from the water being dissipated across a wide braidplain, water is forced into narrow channels, and so it flows much faster. During floods, there is simply too much water, so the river bursts out of confinement. It scours the riverbanks, tears out trees and structures like fences, and carries them downstream. This now becomes a potentially much more damaging and dangerous flood, as churning water and debris slams into bridges and other critical infrastructure such as electricity pylons, as well as private property. Downstream, fine sediment from eroding riverbanks is deposited as the river slows. This suffocates aquatic habitats and promotes the growth of unwanted algae, leading to a loss in downstream ecosystem services and mahinga kai.
- Maintaining weed-free or at least a very low levels of invasive weeds across braidplains helps mitigate these potential impacts from flooding.
- Braided river birds also need weed-free habitats to breed. Along with native fish and invertebrates, they are essential parts of a healthy braided river ecosystem. Protecting their habitats by weeding and trapping predators helps maintain essential ecosystem services including nutrient recycling and pollination.
- These ecosystem services include long-term carbon sequestration in the peaty carbon-rich soils of the lakes and wetlands, which have accumulated over thousands of years. Protecting them helps prevent the loss of this carbon and enables the ongoing draw-down of more carbon dioxide.
- Actively engaging in public awareness of the problems facing this environment helps the community make better-informed decisions about the role of native ecosystems, including their role in sequestering carbon, and the future management of these globally rare environments.
More information
Setting up and using the DOC200 trap