Darwin Rural Groundwater Watch

In the Top End, most rural residents and growers access groundwater via a bore. In fact, in the Northern Territory (NT) 90 per cent of the fresh water supply comes from groundwater, compared to 22 per cent worldwide.

Groundwater comes from rainfall, water not used by vegetation filters through the soil until it reaches the saturated zone as groundwater recharge.  The water table or level in an aquifer will rise and fall depending on variations in recharge. Aquifers can also get water from rivers and streams draining into the ground. Due to the seasonality of rainfall in the Top End, the majority of rainfall recharge happens in the wet season. The groundwater systems that underlie the Darwin rural area 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. This year's wet season has been below average to date, although recent rainfall has seen water levels in some areas steadily increase.

What are the current aquifer levels?

In the NT, groundwater levels are monitored, through a system of 150 instrumented bores and 250 plopped bores. This information is compiled into hydrographs showing the depth from the ground surface to the water table over time. The Department of Environment and Natural Resources (DENR) website hosts the Darwin Rural Groundwater Watch. This is an interactive map which shows the main Darwin rural aquifers, hydrographs of the aquifers levels and lists the latest water level for that aquifer.

What can I do?

1. Use water wisely

   Being careful with water can extend its availability. Check your irrigation and fix leaks to reduce water wastage. Consider the crop water usage when planning your dry season crops.

   Know how much your plants are using and which ones can have their water reduced. Mangoes have a system where partial root zone dryness sends signals to the plant to close stomata and reduce water loss. Sapindaceae (rambutan) lack this signal and do not respond the same way to soil dryness.

2. Know your bore

   Specifically, what the groundwater level depth is in relation to where your bore screens are.  Bores may start to take in sand and silt causing bore failure so make sure you clean and maintain your pump.

3. Watch out for salinity
   
   When aquifer levels get low some systems (Lambells Lagoon and Middle Point) are potentially at risk of salt water intrusion into the groundwater.  If your orchard is in either of these aquifers, keep an eye on your salinity levels, the level of salt in water affects how suitable it is for irrigation. Read the information sheet on Agriculture Victoria's website on measuring the salinity of your water and what it means in an agricultural context. Monitor the pH and electrical conductivity/salinity levels in your water and keep track of how your water quality is tracking over the dry season. There are relatively cheap hand held meters growers can buy (Hanna or Eutech Instruments) as well as pH strips (like pool shop ones).

The following table from the United Nations Food and Agriculture Organisation (FAO) crop salt tolerance data lists some generic salt tolerances for different crops that can be used as a guideline, noting that varieties, rootstocks etc can change these figures.

Key: T- Tolerant, MT –Mildly Tolerant, MS- Mildly Susceptible, S- Susceptible,

Where can I get more information?

For agronomic advice, contact DPIR, Email: horticulture@nt.gov.au or phone Matt Hall 0422 938 529

For information on groundwater, visit the Darwin Rural Groundwater Watch on DENR's website

For water licensing information, visit the DENR Water Licencing Portal on DENR's website

For DENR publications on water, including a preliminary assessment of groundwater use in parts of Darwin and the Koolpinyah report, visit the DENR water publications page

Or for contact DENR’s Water Resources Division

Phone: 08 8999 4455

Email: waterresources@nt.gov.au

DENR release their groundwater level predictions for the end of the dry season in May, so keep your eyes out for that information. It can be found in a number of places, including the DENR facebook page, DENR website, local newspaper, NT Farmers E-news, ABC country hour, and the mid-year edition of Top Paddock.