Christchurch obtains all it's drinking water from under the ground.
Within the layers of gravels, silts, sands and clays that make up the Canterbury Plains, is one of our most valuable resources GROUNDWATER.
Christchurch obtains all it's drinking water from under the ground.
350,000 people drink this water, which is of very high quality. Christchurch is lucky, because in most parts of New Zealand water must be treated with chemicals before people can drink it. Not so in Christchurch. Our groundwater is a valuable resource which we should protect and conserve so we can continue to use it in the future.
Where does our groundwater come from?
Top
If you could follow the path of the water that flows through the plains, you would find that much of it is very old, and originates from snow, rain and ice of the Southern Alps and the foothills.
The groundwater flows eastward towards the sea through layers of gravels called aquifers. The aquifers are permeable, which means that there are small spaces between the gravels and this allows water to flow through them.
Between the layers of gravels are layers of fine sands, clays and silts which are impermeable. This impermeable layer stops the water from moving freely up and down. The result is that under the city there are a series of distinct layers or water bearing aquifers.
The aquifer nearest the surface is called the Riccarton aquifer. This aquifer contains water from the mountains and foothills, but is also recharged by water entering it from the Waimakariri River.
Schematic cross section of Canterbury aquifers.
Water drilling rig.
The water in the top aquifer which is where Christchurch gets much of its water, is not very old, perhaps in the 10s of years. The next layer, the Linwood Aquifer, is much older, in the 100's of years.
As Christchurch gets larger, more and more water is being taken from the top layer. This is causing concern as water levels may drop in this layer.
Spring-fed Streams
Top
Most of Christchurch's waterways are spring fed. This means that their base flow comes from ground water oozing up from below the ground surface.
Unfortunately, some of Christchurch's springs have disappeared, especially in the smaller waterways associated with the upper tributaries. These natural waterways are now dry except for when it rains when they carry rainwater. The lack of spring water can affect the habitat of plants and animals that live in our waterways, including eels, pukeko and damsel flies.
Issues that affect the groundwater resource
Top
|
Local effects Cumulative effects Effects on stream flows Saltwater intrusion Land subsidence |
Stormwater Hazardous substances and Chemical spills Underground Storage tanks Septic tanks |
Local effects
When too much water is pumped out of the ground it can effect the amount of water available to nearby users.
Cumulative effects
If the rate of water being pumped out of an aquifer is faster than the amount of water flowing into it, this can reduce the amount of water available for users.
Effects on stream flows
Groundwater levels determine whether or not our streams our fed by spring water. If groundwater levels are too low, natural waterways with permanent water flow can dry up.
Saltwater intrusion
If too much water is taken too quickly out of the aquifers and the water level drops to a level lower than sea level, saltwater from the ocean can then flow westward into our groundwater. Saltwater would then pollute the ground water making it unsuitable for drinking.
Land subsidence
This may be a problem in the built up parts of the city where there is a lot of construction.
Stormwater
Stormwater is rainwater, which runs off hard surfaces such as roads and roofs. This water can collect contaminants as it flows across the different ground surfaces and seeps through the ground, causing pollution of the groundwater. Contaminants could include chemicals on industrial sites, and fertiliser from farm paddocks.
Hazardous substances and Chemical spills
Hazardous substances can reach groundwater by:
Septic tanks
There are still some parts of Christchurch and also many areas throughout Canterbury that rely on this form of waste storage. Again if these tanks have been incorrectly installed or are damaged, they can pollute the groundwater.
|
Christchurch City Council PO Box 237, Christchurch, New Zealand Ph +64 3 371-1270, Fax +64 3 371-1384 |
©
Christchurch City Council |