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Darwin Rural Groundwater Watch
The Water Resources Division is advising residents of the Darwin Rural area reliant on groundwater that water levels are low – and predicted to decline over the coming dry season.
Groundwater is recharged during the wet season, with groundwater levels rising and then declining through the dry season.
The decline is due to both natural drainage and use. Groundwater levels in the rural area are the lowest recorded since 2006, as a result of back to back poor wet seasons.
Areas most likely to be affected are Howard Springs, Girraween, McMinns, Herbert, Lambells Lagoon and Berry Springs.
These areas have high demands on water use and have underlying aquifers with limited storage capacity.
An aquifer is not a large underground lake. It is a body of rock that contains water in cracks, pore spaces and cavities.
They are also connected to and naturally discharge into rivers and springs such as Howard River, Howard Springs, Whitewood swamp, Black Jungle, Melacca swamp and Berry Springs.
As groundwater levels drop, properties with bores screen/slots at depths within a 10 metre range of expected end of dry season water levels are at risk.
Residents are encouraged to be careful with their water use to extend its supply, and to seek advice on the bore screen height records maintained by the Water Resources Division.
This information will help you determine bore failure risk, and be alerted so that you can make the necessary plans for a temporary water supply.
This video demonstrates how groundwater is recharged during the wet season. This information will help you better understand the water cycle.
Water level Information
Groundwater is the Territory's largest freshwater resource. The population in the Darwin Rural area has grown and so has the demand on groundwater. However, groundwater is not infinite.
Rainfall determines how much groundwater is available and the water table can rise and fall due to a number of factors:
- Rain will raise the water table;
- Lack of rain will lower the water table; and
- Intensive pumping of groundwater can lower the water table.
Hydrographs provide a picture of how the water table in a bore varies over time. As the name suggests they are graphs. They show the depth from the ground surface to the water table plotted against time.
The following hydrographs are from different monitoring bores located throughout the Darwin Rural area.
Map and factsheets
- Darwin Rural Groundwater Watch
- Map of risk area
- Bore construction in shale country
- Bore construction in dolomite
- How to read your statement of bore
- How to find a bore and bore report
- Groundwater Predictions Report
Contact Water Resources Division on 8999 4455 or send us an email:
15L/s Exemption Removal
The Northern Territory Government has amended the Declaration of Exemptions under the Water Act. The new declaration removes the exemption for bores pumping less than 15 L per second from licencing requirements under the Act.
This means people using water through bores, other than for stock and domestic use in the Darwin Rural Water Control District are required to obtain a Water Extraction Licence. Read more
What can residents do
Reduce your water use
The groundwater predictions for the end of this dry season are based on current estimations of water use. This trajectory can be slowed by careful use of water over the dry season.
A collective reduction in water use will extend the available water for this dry season, until the wet season rains fall again and recharge the aquifer.
Garden use if the largest users of domestic water supplied.
Use less water in the garden by:
- Mulching, it keeps soil cool and reduces evaporation by up to 70%.
- Wetting agents will retain moisture and help nourish lawn and plants during the dry season.
- Lawn, try reducing your watering, put a small sized tuna can on the lawn, once it is full your lawn has had sufficient water.
- Pump your bore at a lower rate if possible.
- Use pool and spa covers, they work by insulating the water from wind and evaporation, cover the pool or spa during the dry season or when not in use. This can reduce evaporation or water loss by up to 90%.
Use less water in the home:
- Take shorter showers
- Install dual flush toilets
- Install water efficient products, washing machines, dishwashers, toilets, taps and shower heads. Most products are labelled with a star rating (the more stars the more water efficient). www.waterrating.gov.au
Know your bore
Bores are a narrow hole drilled down into an aquifer to extract groundwater. Bores, like any plumbing device are subject to degradation and even failure. This can be due to age or improper design.
Domestic bores are typically lined with 150mm steel or PVC pipe to prevent the hole from collapsing.
The pipe is perforated with slots opposite the aquifer to allow water to enter.
Special borehole pumps are placed in the bore with their inlet located at some distance above the slots.
When the pump is turned on it causes a localised cone shape drawdown of the watertable around the bore.
The cone gradually expands away from the bore until a balance is reached between the amount of water pumped and the rate of inflow from areas of the aquifer surrounding the cone.
A domestic bore would typically influence the surrounding area by a few tens of meters.
When the pump is turned off the watertable gradually returns to close to its original level. Information about most bores is registered with Water Resources Division.
This information includes:
- Registered Bore Number. All bores in the NT have a unique registered bore number.
- Depth and type of construction
- Location of screens/slots
- Water quality at the time of construction
Problems with bores
Being aware of the signs of bore failure will allow you to plan for a new or extended bore or to plan for a temporary contingent water supply.
The following are signs of bore failure.
- Pump spurts (water and air)
- No water
- Change in water quality
- Discoloured water or sediment/sand in water
- Reduced pressure/pumping rate (less sprinklers running than previous)
- Pump switches off (overheat sensor)
What are the causes of bore failures?
Low water levels are not the only reason for bore failure or inefficiency, which can result from any of the following.
- Use of inappropriate materials or improperly placed screens/slots.
- Borehole instability – damaged casing and screens, borehole wall collapse due to, corrosion or excessive water flow in the bore.
- Biofouling – installing and pumping a bore in some aquifers can increase the amount of oxygen and nutrients in the water. Bacteria such as iron fixing bacteria, can thrive under these conditions.
This is quite common in bores throughout the Darwin rural area.
For more information on this topic please refer to our Iron fouling of Groundwater factsheet on our website.
- Corrosion – Some groundwaters are slightly acidic and can eventually corrode metal bore casings.
- Over pumping – This is the most common issue that leads to premature bore problems. It not only depletes the groundwater, but it rapidly increases the rate of corrosion, incrustation and biofouling related issues. It can also increase the amount of sediment particles moving toward the bore causing plugging of the screens or perforated casing where water flows into the bore.
What action can be taken?
Many problems with bores can be fixed either by the way they are operated or with maintenance.
In some cases the option may be to drill a new bore, reconstruct or deepen the existing one. The first actions to be considered include:
- Reduce water usage.
- Reduce the pumping rate if possible.
- Lower the pump if possible.
- Have the bore cleaned to remove sand and silt as well as encrustation in the slots
Be prepared, diversify your water supply
Now is the time to consider diversifying water supply and storage options, not just for this season, but for seasons to come.
Residents may consider some of the following options.
- Rainwater harvesting. Rainwater tanks are a great way to capture and store water for use in the house or garden.
- Install a smaller yielding pump into your bore.
- Install additional storage tanks to meet water requirements
- Shallower bores may need to be drilled deeper or replaced by one that taps into another aquifer.
- In the very short term water cart suppliers and options for emergencies should be considered.
Frequently Asked Questions
I live in the rural area, could I be affected?
Yes, everyone in the Darwin rural area is advised of the potential risks. Some areas are greater in risk than others as highlighted in the risk map. We have experienced two poor wet seasons and all local aquifers in the Darwin rural area have not fully recharge/refilled. Water Resources has monitoring bores in a number of strategic locations however there are some areas where we do not have these monitoring bores, which means these unmonitored areas could be at risk too.
Why is this suddenly an issue?
We have been very fortunate in the past 30 years to have had above average wet seasons and we have taken this for granted. We have now had two successive poor wet seasons. Rainfall in our region directly affects the amount of groundwater we have to use during the dry season. Every bore user needs to use this resource sparingly and look at alternative options such as rainwater tanks to diversify their water supply, reuse, recycle grey water and make water saving choices for their household and garden.
Where do I find out what the current groundwater levels are?
Water Resources will be providing regular updated groundwater level information on our website: https://denr.nt.gov.au/land-resource-management/water-resources
This information will also be published regularly in the NT News and Rural Weekly newspapers.
You can also phone us Tel: 8999 4455 or email: firstname.lastname@example.org
How do I determine if I will have a water supply problem in November?
The first thing you need to check is the depth of your bore pump and what the watertable level is. For most, the pump will be set just above the screens. It will also help if you know what your pumping rate is and how your bore performs at that rate. As a general estimate, wherever you are, groundwater levels will decline a further 10m. So, if you add 10m to the current water level and if this is at least a few meters above your bore screens, then you probably will be OK.
Where are the screens in my bore?
You can check your ‘Statement of Bore’ report as highlighted below. You can access your ‘Statement of Bore” from our website: denr.nt.gov.au/ by using our Find your bore report on NR Map guide: https://nt.gov.au/environment/environment-data-maps/natural-resource-maps-nt or contact our Darwin office on 8999 4455.
Add 10m to the current water level and if this is at least a few meters above your bore screens, then you are probably OK. If you are below you are potentially at risk.
What signs do I look for, that indicate my bore supply is failing?
The pump discharge is spasmodic with spurts of water and air.Usually, pumps are fitted with an overheat cut-off and so the pump will switch off automatically.Also, if you notice that the pumping rate has reduced (eg. runs less sprinklers than previously), then this may serve as a warning. If you maintain pumping at a reduced rate for too long, the pump may switch off due to overheating.
What options are available to get a water supply?
- Cart Water – commercial services are available or purchase a water cartage tank to fill from a standpipe
- Lower the existing pump (possibly)
- Install smaller yielding pump
Is my bore registered and how do I find out?
You can check on our website denr.nt.gov.au go to the “Maps” promotion box at the bottom and once in NR Maps as shown on the image deselect layers such as bushfires, flora and fauna. Select Water Resources open this and select bores, open this and select NT bores. This will show all bores on the map you can then zoom into the location and check if a bore is located on your property, it will also provide the RN number eg. RN031660.
If your bore is not showing up on the map it is not registered.
What are Power and Water doing?
Power and Water are licenced to take water for public water supply. They are currently using 68% of their licence entitlement. They too have been promoting through their Living Water Smart Program the wise use of water.
What are you doing about horticulturalists and commercial water users?
The majority of water users in the rural area are stock and domestic, large horticulturalists and commercial users are already licenced and their water is metered and accounted for. Everyone needs to use water efficiently and keep an eye on their bore performance in coming months.
What are you doing about private rainforests and forests of lawn?
Everyone needs to take responsibility for looking after our groundwater resources. In times like this watering gardens should be reduced to ensure you and your neighbours have enough water for drinking and household requirements. Residents are encouraged to investigate using grey water and recycling water to use on their gardens.
What is happening about sub-division developments in the rural area?
In some places where it is not sustainable to take groundwater from aquifers, developments are being advised to look at alternative water supply options such as linking to the reticulated supply or invest/encourage rainwater harvesting. Many parts of Australia have similar water issues where rainwater tanks are used widely to supply household water requirements.
Where do I get a water meter and how much would it cost?
Water meters are a useful tool to work out how much water you are using. They can be bought from irrigation, plumbing and pump supply businesses. They range in price depending on the size of your pipework. Ensure the meter is installed as per the manufacturer’s recommendations.
Is Water Resources interested in my water use information?
Yes we are, you can send in your meter readings via our website: www.nt.gov.au/environment/water/water-meter-reading-form of Email: email@example.com or
Phone: (08) 8999 3632. Supporting information we would require includes: Your name, property/parcel no; meter ID, reading date, meter reading.
Last updated: 20 April 2017