Groundwater is water that comes from the ground that's travelled through the soil to underground 'aquifers'. Aquifers are porous geological formations often gravel and sand which act like a sponge, soaking up and storing water.
Poverty Bay Flats
Groundwater is the main source of water in the middle of the Poverty Bay Flats away from the Waipaoa River. The aquifers supplying groundwater were formed from gravel deposits left behind by the Waipaoa River over many thousands of years.
Groundwater in the Gisborne region is used for the irrigation of crops, water for stock and to provide vital backup drinking water when other sources are not available. Groundwater's particularly important as the rivers and streams of the region all typically have low flows in summer.
Almost all the known groundwater aquifers in the region are located on the Poverty Bay Flats. There's over 1400 bores on the Flats drawing water for irrigation and domestic use.
There are also shallow unconfined sand aquifers at Tolaga Bay, Tokomaru Bay, Ruatoria, Tikitiki and Te Araroa.
Groundwater of the Tūranga Poverty Bay Flats
Beneath the surface - understanding groundwater of the Tūranga Poverty Bay Flats, protecting our resources, the current state, testing the model, results and what's next.
For full view Beneath the surface
Aquifers in Poverty Bay
A gravel aquifer that can be encountered at depths of 45-80m depending on location and ranges in thickness from 5-15m.
- Aquifer is the most utilised in this region and is under some stress with water takes ranging from 100-6000 m3/day.
- Seasonal water level fluctuations tend to be within 5-10m, therefore submersible pumps are recommended as they are not limit by lift capacity.
- Surface pumps are not recommended as a reliable efficient extraction system during the peak of summer as generally they only have a lift capacity of 4-6m.
- Water quality is variable.
Refer to the Managed Aquifer Recharge project webpage.
A narrow gravel aquifer that can be encountered at depths of 90-140 metres in the subject area.
A shallow sand aquifer that can be encountered just below the topsoil and can be up to 20 metres thick.
- Aquifer is under little stress and has water takes ranging from 45-1850 m3/day.
- Seasonal water level fluctuations tend to be within 0.5-1 metres, therefore surface pumps are usually sufficient to extract water.
- Water quality is variable.
Gravels laid down within the meandering river channel cut into fluvial, swamp, lagoon and estuarine sediments.
- Aquifers located at depths of 15-30 metres
- Recharge likely to be from the Waipaoa River.
- Aquifer appears to vary in water level by 1-2 metres between winter and summer.
Shallow fluvial deposits are also found at depths of 0-20 metres at a number of locations around the Flats and can be up to 10 metres thick.
Gravels aquifer that can be encountered at depths of 10-30m depending on location.
- Seasonal water level fluctuations tend to be within 1-3m.
- Water quality is variable and further information is available by contacting our water resources team.
Bore permit and water take requirements
You need to apply for a bore permit to install any type of bore. We record all bore locations.
A bore permit doesn't mean a water permit will be issued to take water from the bore.
Water for your property
You're permitted to take water for your property, provided you meet the following:
- maximum water take is up to 10 cubic metres per day, and
- water must be taken at rates of less than 5 litres per second, and
- you must not irrigate more than one hectare.
Water takes over these limits require a water take consent.
Stock drinking water
Water for stock drinking needs to be taken at less than 5 litres per second.
To apply for a bore permit or water take consent - see Resource Consents forms
Using groundwater
A bore or well can be drilled into an aquifer and secured with a casing pipe which brings the water to the surface.
The cost of installing a groundwater bore depends on the depth and how the water is to be pumped. Pump testing of the bores is sometimes required to find out if it's having a negative effect on neighbouring properties. A pump test also provides council with valuable information that can determine the storage capacity and how quickly the aquifer can recover from pumping for an individual bore.
For bores that are used all summer, a submersible pump is recommended. This is because water levels can drop below the lift capacity of most surface pumps. A screen should be fitted at the bottom to avoid the pipe or pump from clogging.
Watertables
The groundwater travels through the soil until it reaches a depth where the sediments are filled with water - the 'saturated zone'. This process 'recharges' the groundwater supply. The top of the saturated zone is called the water table in an unconfined aquifer and may be very close to the ground surface or many metres down.
Groundwater can also be recharged when water from rivers or streams travels down through the riverbed to replenish the aquifer below.
In Gisborne, water entering through the groundwater system beneath the Poverty Bay Flats flow towards the coast through the sediments. Although - with the exception of the Te Hapara sand aquifer - the aquifers have no direct connection with the sea.
Potential groundwater contaminants
Groundwater is not protected from contaminants. Soil can act as a filter, although it's not able to filter out all impurities.
Contamination of groundwater can happen gradually and go unnoticed for some time. Most contaminants come from the ground surface, shallow watertable aquifers with thin soil cover are easily contaminated.
Contamination of groundwater can come from:
- animal effluent
- fertilisers and pesticides
- leakage from pipelines and underground storage tanks
- salt water intrusion.
Because the flow of groundwater is slow with little turbulence, contaminants are not easily diluted or dispersed. Pollution can therefore stay a long time in groundwater and can be very difficult or impossible to clean up.
Naturally occurring contaminants include minerals which dissolve out of the surrounding rock such as iron, calcium, magnesium and manganese. These are generally only a nuisance, at worst - clogging irrigation nozzles, rather than being a risk to human health or the environment.
Helpful link for consent holders
Ministry for the Environment's guide for measuring and reporting water takes