Darwin Rural Groundwater Watch
Where does your water come from?
Most rural residents access groundwater via a bore.
Underlying the rural area there are many different groundwater systems.
How are our groundwater systems different?
Groundwater is the water that fills the spaces, cracks and crevices in rock, sand/gravel. The different types of rocks that underlie the rural area vary depending on where you live. It is the rock type that determines how much water it can hold, how water moves through it and how much can be pumped out.
Our groundwater systems are fill and spill in nature
The groundwater systems that underlie the Darwin rural area rely on wet season rainfall to replenish each year. They are known as fill and spill systems as they do not have large storages. In above average rainfall years they will refill and the excess water will spill out into our waterways. In the past 30 years we have had above average wet seasons and we have taken this for granted. The Darwin rural area had two successive poor wet seasons in 2014 to 2015 and 2015 to 2016. Groundwater levels were low, if not the lowest, on record.
This year’s outlook
We had an above average 2017 to 2018 wet season. This enabled full recharge or refilling of our groundwater systems. Groundwater levels were predicted to return to average end of dry season levels for all groundwater systems except Berry Springs.
Berry Springs is now at moderate risk with groundwater levels dropping below average. Water supplies drawn from shallower bores in this area may be impacted.
Groundwater levels at Humpty Doo, Girraween/McMinns and Howard Springs are still declining. The risk is low but moving towards moderate.
It is important to stress that being careful with water use will extend its availability. Until the wet season rains fall again and replenish our groundwater systems.
Water level information
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.
The below hydrographs are updated at the end of the month, to provide up to date information in your area.
- Lambells Lagoon area
- Middle Point area
- Berry Springs area
- Howard Springs area
- Herbert area
- Humpty Doo area
- McMinns/Girraween area
- Howard Springs - Mt Partridge
Map and factsheets
- Bore construction in shale country
- Bore construction in dolomite
- How to read your statement of bore
- How to find a bore and bore report
What can residents do
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 metres.
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 possible 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 refer to the Iron fouling of Groundwater factsheet.
- 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.
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 wet season rains fall again and recharge the aquifer.
Garden use is the largest user of domestic water supplies.
Use less water in the garden by:
- Mulching, it keeps soil cool and reduces evaporation by up to 70%.
- Using a wetting agents to 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%.
- 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
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 carting suppliers and options for emergencies should be considered.
Contact Water Resources Division on 08 8999 4455 or send us an email: email@example.com
Last updated: 29 November 2018