<p>One cannot discount the fact that the northern islands
of Indonesia Timor island and Papua New Guinea are
very high precipitation areas.  It has been documented
that there is high groundwater movement under Sahul
shelf off Timor Island.  The same Sahul shelf is also
between Papua New Guinea and Australia.  Since there is high groundwater movement off of Timor Island there is
a high probability there is between Cape York and
Papua New Guinea shore line.  So GAB could be replenished by the Northern Islands of Timor and
Papua New Guinea.</p>

CC BY-SA 4.0
2021-11-25T10:28:21.713Z
I think Occam's razor applies here. The recharge zones and direction of groundwater flow can be determined by piezometry. Isotopic data can also tell us something about groundwater age and the conditions when it was recharged.  Without compelling evidence that the GAB water balance is poorly understood, there's no need to invoke hypothetical flows from the north, especially when there is evidence from drilling that the aquifer system doesn't extend right across the straits.
Andy M
CC BY-SA 4.0
2021-11-24T16:04:40.273Z
2021-11-24T16:04:40.273Z
tom
<p>Most of the underlying strata beneath the Gulf of Carpentaria seabed is part of 
the Great Artesian Basin (GAB).  It extends out to the Arafura Seabed and west
of the Torres Strait islands.  It may even extend or connect with paleochannels
of Papua New Guinea's (PNG's) coastal areas.  Geoscience Australia has maps showing the northern borderline or "country" maritime border areas of GAB.  One could assume that GAB probably goes all the way to the PNG coastline.  CSIRO and Geoscience do not provide maps detailing the geology  under the Arafura Seabed or Torres Strait seabed close to the PNG coastline.</p>

CC BY-SA 4.0
2019-08-16T14:37:50.420Z
2019-08-16T15:52:43.580Z
2019-08-16T15:52:43.580Z
George
<p>In the far north of the Great Artesian Basin, there is groundwater outflow to the Gulf of Carpentaria. Everywhere else the aquifer behaves as a closed basin with outflow in the form of vertical seepage (e.g. to the Mound Springs of South Australia), artesian overflowing boreholes, and pumped boreholes. There may once have been hydraulic connection to the Southern Ocean, but that ceased several millions of years ago - not such a long time when one considers that the longest through-flow time of groundwater, from east to west, is about two million years. </p>

<p><a href="https://i.sstatic.net/GJoUM.gif" rel="nofollow noreferrer"><img src="https://i.sstatic.net/GJoUM.gif" alt="enter image description here"></a></p>

CC BY-SA 3.0
2015-10-25T22:18:37.697Z
@GordonStanger what is the distinction between "Intake Area" and the GAB in that map?
Eubie Drew
CC BY-SA 3.0
2016-04-04T19:13:27.330Z
I take intake area to be that plan area where recharge exceeds discharge.
Gordon Stanger
CC BY-SA 3.0
2015-10-08T07:38:17.760Z
Appreciate! According to your answer, the GAB as a whole is not a closed basin. Is there a maximum sub-region of GAB that only has vertical hydrologic exchange? I want to know a maximum region that the boundary has no lateral hydrologic exchange.
StonerYancy
CC BY-SA 3.0
2015-10-09T09:38:49.953Z
Not quite sure what you mean. All of the GAB has a lateral component in the form of lateral inflow from the recharge zone on the eastern boundary. Do you mean 'how much of the perimeter is effectively impervious'?
Gordon Stanger
CC BY-SA 3.0
2015-10-10T01:25:52.490Z
Actually I got confused about the definition of "closed basin" or "endorheic basin". Sorry about that.
StonerYancy
CC BY-SA 4.0
2019-08-16T16:30:08.947Z
@StonerYancy I'm still confused about the difference between a closed basin and an endorheic basin (not my area). But I guess that's a different question!
Semidiurnal Simon
CC BY-SA 4.0
2019-08-16T16:36:18.250Z
....a different question that I've now asked at https://earthscience.stackexchange.com/questions/17758/what-does-a-closed-basin-mean-in-groundwater-terms
Semidiurnal Simon
CC BY-SA 3.0
2015-10-08T06:57:20.997Z
2015-10-25T22:15:36.987Z
2015-10-25T22:15:36.987Z
Gordon Stanger
<p>Areas where topography prevents the outﬂow of water are called closed basins. Is the GAB a closed basin? What if external bodies of water flowed in? Is that still "closed"?</p>

CC BY-SA 3.0
2015-10-08T00:18:04.427Z
See related question about inflows to the GAB: http://earthscience.stackexchange.com/questions/4466/source-of-water-for-the-great-artesian-basin-in-australia
Fred
CC BY-SA 3.0
2015-10-09T03:18:15.950Z
Are you asking about surface water flow or groundwater flow?
haresfur
<hydrology>
Is the Great Artesian Basin a closed basin?
StonerYancy
# Is the Great Artesian Basin a closed basin?

(Asked by: username_0 on 2015-10-07)

Areas where topography prevents the outﬂow of water are called closed basins. Is the GAB a closed basin? What if external bodies of water flowed in? Is that still "closed"?

**Tags:** hydrology

> **Comments:**
> **username_1**: See related question about inflows to the GAB: http://earthscience.stackexchange.com/questions/4466/source-of-water-for-the-great-artesian-basin-in-australia  
> **username_2**: Are you asking about surface water flow or groundwater flow?  

---

## 3 answers

### Answer by username_6 on 2015-10-08. Score: 3 | Accepted answer

In the far north of the Great Artesian Basin, there is groundwater outflow to the Gulf of Carpentaria. Everywhere else the aquifer behaves as a closed basin with outflow in the form of vertical seepage (e.g. to the Mound Springs of South Australia), artesian overflowing boreholes, and pumped boreholes. There may once have been hydraulic connection to the Southern Ocean, but that ceased several millions of years ago - not such a long time when one considers that the longest through-flow time of groundwater, from east to west, is about two million years.

[![enter image description here](https://i.sstatic.net/GJoUM.gif)](https://i.sstatic.net/GJoUM.gif)

> **Comments:**
> **username_0**: Appreciate! According to your answer, the GAB as a whole is not a closed basin. Is there a maximum sub-region of GAB that only has vertical hydrologic exchange? I want to know a maximum region that the boundary has no lateral hydrologic exchange.  
> **username_6**: Not quite sure what you mean. All of the GAB has a lateral component in the form of lateral inflow from the recharge zone on the eastern boundary. Do you mean 'how much of the perimeter is effectively impervious'?  
> **username_0**: Actually I got confused about the definition of "closed basin" or "endorheic basin". Sorry about that.  
> **username_7**: @username_6 what is the distinction between "Intake Area" and the GAB in that map?  
> **username_6**: I take intake area to be that plan area where recharge exceeds discharge.  
> **username_8**: @username_0 I'm still confused about the difference between a closed basin and an endorheic basin (not my area). But I guess that's a different question!  
> **username_8**: ....a different question that I've now asked at https://earthscience.stackexchange.com/questions/17758/what-does-a-closed-basin-mean-in-groundwater-terms  

---

### Answer by username_3 on 2021-11-24. Score: 0

One cannot discount the fact that the northern islands
of Indonesia Timor island and Papua New Guinea are
very high precipitation areas. It has been documented
that there is high groundwater movement under Sahul
shelf off Timor Island. The same Sahul shelf is also
between Papua New Guinea and Australia. Since there is high groundwater movement off of Timor Island there is
a high probability there is between Cape York and
Papua New Guinea shore line. So GAB could be replenished by the Northern Islands of Timor and
Papua New Guinea.

> **Comments:**
> **username_4**: I think Occam's razor applies here. The recharge zones and direction of groundwater flow can be determined by piezometry. Isotopic data can also tell us something about groundwater age and the conditions when it was recharged.  Without compelling evidence that the GAB water balance is poorly understood, there's no need to invoke hypothetical flows from the north, especially when there is evidence from drilling that the aquifer system doesn't extend right across the straits.  

---

### Answer by username_5 on 2019-08-16. Score: -1

Most of the underlying strata beneath the Gulf of Carpentaria seabed is part of
the Great Artesian Basin (GAB). It extends out to the Arafura Seabed and west
of the Torres Strait islands. It may even extend or connect with paleochannels
of Papua New Guinea's (PNG's) coastal areas. Geoscience Australia has maps showing the northern borderline or "country" maritime border areas of GAB. One could assume that GAB probably goes all the way to the PNG coastline. CSIRO and Geoscience do not provide maps detailing the geology under the Arafura Seabed or Torres Strait seabed close to the PNG coastline.


---

