Mulgrave Landcare – Mulgrave Aquifer


Mulgrave Aquifer

Please be advised that the content on these pages is the sole responsibility of Mulgrave Landcare & Catchment Group.

Cairns Regional Council (CRC) intends to harvest underground water from the Mulgrave Aquifer to contribute to existing city water supply from Copperlode Dam and Behana Creek at Aloomba. As this could affect the dry season water levels of the Mulgrave River and Behana Creek in particular, you may be interested.

What is an aquifer?

Aquifers are underground layers of permeable rock or uncompressed sands & gravels that contain enough mobile water that they can be tapped into by wells and bores and the water removed from the spaces between the rock or gravel particles. Some aquifers, like the great Artesian Basin of Western Queensland are naturally pressurized with water flowing up to the surface unassisted once a bore is sunk down to the underground water level. In our coastal areas they are usually not pressurized and the free or available water has to be sucked out of the gravels and brought to the surface by pumping. The quality of underground water varies greatly, depending largely on the type of the surrounding rock and soil and on the land-uses within that water catchment.

Where is the Mulgrave Aquifer?

Just south of Cairns, the Mulgrave Aquifer underlies all of the alluvial plain from the southern side of Trinity Inlet, under and east of Edmonton, under Greenhill and Gordonvale and under the full length of the Mulgrave River Valley from Little Mulgrave to Russell Heads.

The aquifer sections under the present Mulgrave River are the result of thousands of years of sedimentary deposits, which loosely hold the underground water, accumulating from river movements and floods across the valley over that time. The deposits north of about Greenhill (north of Gordonvale) occurred in the many millennia before that when the Mulgrave River apparently ran North into Trinity Inlet instead of south to Mutcheroo Inlet as it does now.

Click here to download a map of the Mulgrave Aquifer (10Mb file).

The current issue.

The Cairns Regional Council intends to harvest underground water from the Mulgrave Aquifer to contribute to existing city water supply from Copperlode Dam and Behana Creek. Unfortunately though, it appears that even the deep aquifer layers have connection with surface streams, and this is the basic problem – whatever is taken from underground in the dry season will effect the river system by the same amount by altering the near-surface ground-water table.

Because water demand from the population is highest in the dry season and natural-supply is lowest, the amount of water extracted, the location from which it is extracted and time at which it is extracted are of critical importance. If investigations into such harvesting have any error in them at all, the risk of adverse effect upon the water dependent environments of the Mulgrave Valley, and Behana creek in particular, are very high.

It should be noted that though Queensland’s Water Act 2000 provides for the protection of water resources through Water Resource Plans, this landmark groundwater development will be occurring before a Water Resource Plan is in place for the Mulgrave Catchment.

Mulgrave Landcare’s concerns with ground-water harvesting.

There is a history of failed groundwater developments around the world where natural, agricultural and even built environments have been disastrously affected by unforseen consequences of lowered water tables. These problems are usually only obvious after a period of years, by which time it is too late to retreat from the development, reverse the effects or repair the damage.

In Australia, the problems of the Murray-Darling system which include groundwater over-use, the Lockyer Valley in Southern Qld and the Burdekin area south of Townsville are examples. In all cases it appears that early warnings by environmentalists were ignored, investigations into the proposals were not adequate or well scrutinized and now that the long-term effects are obvious, it is too late to do much about them.

With the Mulgrave, our basic concern is that harvesting of groundwater in the Aloomba area as proposed, will result in a significant lowering of the dry-season water table that supports the Mulgrave River, Behana Creek and other streams as they cross the alluvial plain above the aquifer.

Potential effects are:

• Severe reduction in Behana Creek’s dry season flow every year and possible total loss of surface flow in very dry years. (Behana has never previously run dry.)
• Loss of aquatic life in Behana;
• Loss of Behana’s swimming areas;
• Reductions in Mulgrave River dry-season flows (up to 34% lower than previous low flows);
• Critical changes to dry-season fish-breeding & survival in the Mulgrave;
• Loss or critical changes to the riparian (stream-side) vegetation on both streams;
• Loss of critical dry season water levels for the lower Mulgrave Wetlands;
• Changes in water quality resulting from less dilution of contaminants from the licenced waste dump on Behana, a proposed Quarry on Behana, the sewage treatment plant on the Mulgrave,farming activities and storm water from the Gordonvale urban area;
• Ingress of salt into the aquifer from salt-water wedges from Russell Heads (& possibly Trinity Inlet).

These effects would add to the existing pressure imposed on Behana by current surface-water harvesting in Behana Gorge and exacerbated in all streams by the longer and more severe dry seasons that are occurring with climate change.

Below are photos of Behana Creek between the Bruce Highway and the Aloomba causeway. With the aquifer harvesting occurring from as little as 400 metres away, the very low dry season flows could become normal flow for most of every summer (instead of for short, infrequent periods) and could disappear entirely in really dry periods.

Mulgrave Landcare – Mulgrave Aquifer

Aquifer Behana Good flow
Behana Creek: Good summer flow
Aquifer Behana Low flow
Behana Creek: Dry season flow

The proposal to take water from the aquifer

A brief history

Since 2005 CRC , through its Cairns Waste &Water unit, has been investigating the harvesting of underground water from the Mulgrave Aquifer to supplement existing water supplies to the council area to cater for a burgeoning population. Similar use of the Barron River (North of Cairns) has been under investigation simultaneously. Other supply options were considered during this period with some discounted & others relegated as secondary options. All options were primarily considered within the context of a Cairns Regional Council, “Least Cost Water Supply Strategy.”

Both the Mulgrave Aquifer and Barron Schemes were proposed to be developed in two stages, with options ranging from one or the other, to various combinations of the 4 stages, as possibilities. The Barron River option was initially highest preference, but Cairns Water maintain that they were informed that permits to take water from the Barron would not be given until the Mulgrave Aquifer option was investigated & shown to be an unviable alternative.

Subsequently, a number of background ‘studies’, dating from 1998- 2007 were used to construct a Mulgrave River Aquifer Feasibility Study. This was expanded upon to produce the draft MRAFS- Public Environment Report (MRAFS-PER) in mid 2008.This document was released for public comment with submissions due Oct 2008. After supposedly addressing public comment on the draft, a revised and final version was made public in Feb 2010. The MRAFS-PER is the primary document used to by Cairns Water and the Council as justification for the aquifer proposal.

The Mulgrave Aquifer Feasibility Study – Public Environment Report

The core elements of this report are the investigations into understanding the interactions between the ground and surface water systems in the catchment, how they will be effected by aquifer harvesting and how that will in turn effect the catchments’ environmental values.

Our most basic premise is that the quality of these elements within the draft PER were so poor that few if any of the conclusions made in reference to environmental impact could be accepted, and that Cairns Water’s lack of understanding of the dynamic physical system and lack of rigour in applying current best practice to such essential items as environmental flow determination and computer modelling, supported that assertion. Though the final PER has some additional information and comment on concerns raised by public submissions, our opinion is that the quality of content has changed very little and our criticism of the draft report still applies to the final report.

The MRAFS-PER is primarily aimed at the requirements of the Federal EPBC (Environmental Protection & Biodiversity Conservation) process which the aquifer proposal has to adhere to.A feature is that environmentally, it only has to address the potential impact on 13 identified threatened species and any relevant World Heritage areas, collectively known as matters of National Environmental Significance (NES).It does not assess impact on the general environments of the Mulgrave Valley alluvial plain overlying the aquifer, particularly the Mulgrave River, its permanent tributaries, aquatic ecology, riparian habitats, lower catchment wetlands or other groundwater dependent ecosystems.

Click here to view the final MRAFS-PER

Below is our comment on the draft report which is still relevant to the final report. A major concern even before meaningful review could begin, was the unwillingness of the Council to make available essential background reports needed to validate conclusions made in the reports. Click the link below to view our response to the reports. (275KB). Look for the summary of concerns on Page 14.

A very telling aspect of the reports is that the main conclusion made in the text ie that there will be no environmental impact by a 15ML/D abstraction, is contradicted by a table on the bottom of page ii of the executive summary, that shows a predicted drop in water tables of between 2m near production bores and 0.5m at a distance up to 3km from them. Behana Creek is often less than 0.3m deep over much of its length during the dry season and is less than 500 metres from the proposed borefield. A large portion of the middle reaches of the Mulgrave River are also in this radius.

Click here to view Mulgrave Landcare’s submission regarding the MRAFS Public Environment Reports (275KB).

Before the proposal to extract water from the aquifer can proceed, an application by the Council has to go through both a federal process administered by the Department of Environment, Water, Heritage and the Arts (DEWHA), and a Queensland process outlined by the Sustainable Planning Act (SPA).

Click here to view Mulgrave Landcare’s most recent submission to DEWHA 2010.doc.

Where are we now?

As of end February 2010, DEWHA have accepted the final MRAFS-PER for assessment. The result of that assessment is not yet public and indications are that it will be released only after the State SPA process has run. Under DEWHA requirements the PER now has now been publically advertised, though there is no mechanism for further formal public submissions.

It is expected that CRC will very shortly apply to have the State SPA process initiated. Unfortunately, like the DEWHA process, the SPA process will not force assessment of the impact on general environmental values. This is due to the fact that CRC was granted a water allocation (not a development permit), in 2000 under the Water Act 1989, which did not require any assessment of environmental impact. Though the current Water Act 2000 which the SPA process will be considering does include environmental assessment, the conditions of that water allocation will not be re-assessed. Without consideration of the impact of the actual extraction of water on the environment, SPA will only be assessing the totally insignificant impacts of construction works and infrastructure ie. bores, pipelines and small buildings, etc. A very remote chance is that the Minister for DERM (Dept. Environment & Resource Management), can be convinced to intervene.

What can you do to help.

Please take a look at our ‘submission on the MRAFS-PER reports, to gain an understanding of our well considered concerns over the standard of the report behind the application.

If you see or hear comment on the aquifer proposal in the local media, please write or ring in to provide support for our stance.

The relevant departments to write to with your concerns about the Mulgrave Aquifer are;

Cairns Regional Council
Department of Environment and Resource Management (DERM)
Department of Environment, Water, Heritage and the Arts (DEWHA)

Send your letter to us and we will forward it on to them.

Contact Us

Mulgrave Landcare PO Box 215 Gordonvale Q 4865
Ph. (07) 40 561 205; Fax (07) 4056 1205