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The South West Tragedy

South Yarragadee

The South West Tragedy

EPA Chairman Dr Wally Cox said that in giving qualified support to the proposal the EPA has recommended tough conditions that go much further than the actions Water Corporation proposed, to ensure risks to the environment are minimised.

We appeal against the approval of the use of the Yarragadee for the supply of Perth water. Our appeal is based on four main points.


1)We believe that the whole concept of using recharge to justify the approval to abstract 45 GL/yr. is not acceptable, and that the 150 GL/yr estimate of recharge to the confined Yarragadee aquifer is erroneous

2) The draw down estimates based on the modelling are highly reduced

3) The concept of River flow supplementation is flawed.

4) The concepts of transparent monitoring and base line information will never be respected.

The recharge quandary

The approval is based on the assumption that the rate of replenishment of the Yarragadee aquifer is around 150 GL/yr. Several models were used to estimate the groundwater recharge which is based on different methods of water balance and chemical methods. The estimates of recharge to the top unconfined aquifers were found to range from 302 to 306 GL/yr. The estimate with SWAM2 was 374 GL/yr. Although these recharge values are gross estimates, the modellers never showed how the recharge component of the Yarragadee aquifer was derived? There is not a single estimation of the recharge to the Yarragadee. The recharge estimate of 150 GL/yr to the Yarragadee confined aquifers was determined by modelling and has been an outcome of the model calibration process, which is based on several assumed parameters and concocted vertical hydraulic conductivities (as these were never measured or properly estimated).

As a matter of fact and based on the reports produced by the Water Corporation the only replenishment which takes place to the Yarragadee confined aquifers is in the outcrop area and this was estimated to be 35 GL/yr only, which is not even enough to sustain the environmental requirements let alone the local current and future planned abstraction rates.

Strategen in their response to the submissions went to great length to prove that the Mowen Member is formed of clay and silts and is impermeable in most of the South West. “The extensive drilling and down-hole geophysical logging clearly show that the Mowen Member is dominated by clays and silts, with minor sand bedding. The poor vertical permeability is conclusively demonstrated by the high water levels observed at the top of the unit and the large vertical hydraulic gradient through the unit. For these observed levels in water to be maintained in a situation of much greater vertical permeability would require a proportionally greater downward flux of groundwater and unrealistically high levels of groundwater recharge”.
They went further and mentioned that although the Mowen Member covers almost 3000 km2 of the plateau and in these areas, there is a very low risk of watertable changes resulting from pumping from the Yarragadee Formation.”
If all this is true, can Strategen and the modellers explain how 150 GL/yr of recharge is reaching the confined parts of the Yarragadee aquifer?
As for the fallacy of the rejected recharge, we might agree that the recharge will increase to the Superficial aquifer if this amount of water was discharged from the Superficial and Leederville unconfined aquifers. But as STRATGEN and the modellers emphasised the impermeability of the Mowen member, there is no way that this rejected recharge will reach the Confined aquifers.
Any way, the use of recharge to allocate groundwater is an archaic approach which was used in the eighteenth and early nineteenth centuries by conventional hydrogeologists. Numerous international researchers highlighted in several international publications that this antiquated approach caused the depletion of many aquifers in America, South America, Europe and Asia and led to many environmental catastrophes and is causing mayhem in the Gnangara Mound.

Drawdown estimates

The EPA mentioned that the Water Corporation’s proposed well field pumping would see a very significant increase (100%) above the current use, and it would also be much more concentrated than any existing pumping. For this reason, there remains conjecture regarding the confidence of the predicted drawdown.
There is no conjecture that the drawdown will be much higher than predicted for several reasons:
1) The high assumed values of hydraulic conductivities and transmissivity used by the model. These values were obtained by trial and error during the calibration of the model. The only aquifer test was of no use to give reliable value as it was conducted for a very short period of time and the well design was not appropriate to assign the derived values to any of the aquifer layers.
2) The assumed interconnectivity between the unconfined aquifers and the upper and lower parts of the confined aquifer which are contradicted by the presence of the impermeable Mowen member.
3) The assumed rates of recharge which does not exist in the confined parts of the aquifer.

The DoW which is the silent partner and schemer and the inventor of the 1 million GL myth, has advised that it generally considers the interpreted modelled drawdowns to be as sound a prediction as possible, based on the currently available information and knowledge. The DoW knows quite well that the available information and knowledge is not adequate to give this advise, they are also aware that these predictions are not acceptable based on their experience from the Gnangara Mound.

River Flow supplementation

The commitment of the Water Corporation to mitigate the decline in summer base flow in the Blackwood River and tributaries, St John Brook and Milyeannup Brook by supplementation from groundwater from the Leederville and Yarragadee Formations is preposterous. They stated that “pumping rates and annual volumes for supplementation, (if required) are small, being no more than 20 L/s for about three months (155.6 ML/yr) for the Blackwood River, and 5 L/s and 2 L/s for Milyeannup Brook and St John Brook respectively, again for about three months each year. The maximum total annual abstraction, if and when required, would be about 210 ML/yr, and would add about 0.5% to the proposed 45 GL/yr abstraction proposal”.

The important point is that pumping of water to supplement the flow will further increase the drawdown, cease the base flow to the Blackwood River and tributaries, St John Brook and Milyeannup Brook, and will lower the water levels to a point which will endanger all types of vegetation and will require more than the estimated amounts to sustain the flow, as more water will be required first to fill the space between the drawdown levels and the river flow level before flow will take place..
These estimates neglected a very important component, that when the water levels drop, the streams which used to be sustained by groundwater discharge (effluent stream) will become groundwater recharge (influent stream) and more than 100 to 200 times the amount of water which used to flow will be required to bring the water levels back to the river level before a flow in the river can be sustained. It is estimated that more than 2 to 5 GL/yr would be required to sustain the environmental flows.
This is due to the fact that recharge is only taking place in the unconfined parts of the Yarragadee aquifer, which was estimated to be only 35 GL/yr. This discrepancy will cause excessive drawdown which will require more water to fill in the voids.

It is also mentioned that minor treatment may be required to remove iron and manganese, and such treatment (using aeration) would ensure the required dissolved oxygen levels are met. The cost of treating 2 to 5 GL/yr of groundwater, control the temperature and manage erosion by the silt free groundwater at the rising power costs which would have to be arranged at each site would be prohibitive.

Transparent monitoring and baseline information
The EPA mentioned, that the proposal should only proceed after a rigorous and transparent monitoring programme and adaptive environmental management plan is established and implemented, including criteria under which pumping may need to be reduced or cease. It is expected with the severe effects of climate change that the environmental conditions of the South West will change dramatically even without the mining of water from the Yarragadee. It will be impossible to separate the effects of the pumping from the climate change which will be blamed for the change and no action will be taken.
The EPA also recommended that there needs to be a baseline information acquisition and investigation programme, to acquire and establish a comprehensive baseline of bio-physical and hydrological conditions for groundwater dependent ecosystems on the Blackwood Plateau. To establish this base line of information 10 to 20 years of data will be required, will the Water Corporation and the politicians allow for such a period? or it will be rushed after one or two years on the surmise that they discovered that there is enough base line data as is always the case and the project will go ahead with a set of site-specific mitigation and management plans for the Blackwood River, St John Brook, Milyeannup Brook, Poison Gully and Rosa Brook which will be of no use when the disaster occur.

It is not fair

It is not even reasonable to contemplate to import 45 GL/yr of water from the south west, while we in Perth are using more than 200 GL/yr to keep our lawns and gardens green. The south west will need every drop of this water for its own use and for the sustainability of the eco system and the environment.

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