The greatest threats to the springs in the headwaters of the Ōpāwaho Heathcote River are from:
- over-extraction of water from the aquifer
- pollution of the aquifer
- earthquakes, climate change and the natural evolution of the aquifer
Threats and protection
Threats to springs
Over-extraction
While Christchurch has extracted water from its aquifers since European settlers arrived on the plains, the amount extracted by industry, in particular by farming, has soared in recent years. This is due to the use of irrigation to make intensive farming possible on the dry soils of the Canterbury Plains.
The trouble with high levels of extraction is that:
- it can reduce the pressure in the aquifer resulting in lower flows to springs, or for springs to dry up altogether
- the reduced pressure can allow the saltwater in the sea to intrude further up the aquifer affecting the quality of water in the system
Pollution
The water in the aquifers comes from rainfall and irrigation water infiltrating through the soils of the plains, and from leakage from the Waimakariri River. If there is excess nitrogen and phosphorus being placed on the surface soils in the form of artificial fertilisers or urea from cow urine, this is dissolved in the water and makes its way into the aquifer. These chemicals in very low concentrations are toxic for stygofauna and micro-organisms that form the basis of the ecosystem food chains in the streams which these aquifers feed. These chemicals also cause the over-development of algae in the streams which has flow-on effects on the health of the streams.
Christchurch’s water – what’s the story?
Around 369 million cubic metres of groundwater flows out of the Christchurch aquifer system annually. This is made up of:
- 208 million cubic metres that enter spring-fed streams such as the Ōpāwaho Heathcote and the Avon Otakaro Rivers which flow to the estuary and the sea.
- 9 million cubic metres which flows underground to the sea or other springs.
- 152 million cubic metres which is allocated for use by Christchurch for industry (including farming) and for city water supply. Not all of this allocation is used but the proportion of it reserved for industry has been over-allocated.
You can read more about how Environment Canterbury manages the allocation of freshwater from the Christchurch aquifer here
Earthquakes and other natural changes
The 2010 earthquake sequence in Christchurch showed that ground disturbances caused by earthquakes can result in the creation of new springs and the closing down of previously flowing springs. This is a natural part of the evolution of the land and water interface. Springs can also appear as a result of the slow ingress of groundwater that gradually weakens a semi-permeable layer of gravels and clays.
Climate change may also reduce the amount of rainfall that contributes to groundwater recharge.
How to protect our springs
There are many things that we can all do to help protect our springs. We can:
- Understand where springs come from and value them
- Support regulations that control and seek to reduce the impact of farming on groundwater
- Encourage Environment Canterbury to take effective action to protect groundwater from pollution
- Encourage Environment Canterbury to take effective action to reduce the over-allocation of groundwater
- Encourage national government to enact legislation that helps farming and industry to reduce pollution of groundwater
- Make sure that you and your family make effective use of all water used and do not waste it
- Reduce the chemicals that you use on your property
- Help to reduce the impact of climate change by reducing your family’s carbon footprint