Water Management In and Near Quarries

BRUCE McCLURE, CMPA’s General Manager reports on the management of water around quarries which has been an issue for many quarry owners around Victoria over the last four months.

WATER is one of the basic ingredients of life. We personally cannot live without it and every part of our every day existence requires it to various extents.

Australia historically goes through cycles of drought and floods. We have just come out of a dry period which has lasted for around ten years. Th e wet spell that we are currently experiencing has been very severe. Whether or not it is the worst that we have ever experienced is open to debate.

Irrespective as to whether or not it is the worst wet season we have experienced, the flooding has been severe and has had major consequences on a number of quarries around Victoria.

The recent flooding has highlighted a number of issues. However, one issue stands out and that is the lack of construction of new and the maintenance of existing drainage systems throughout many areas.

This is an issue not just for some quarries but is reflected through the general community especially within various municipalities.

Water has made its way into quarry sites from adjoining properties, crown land such as State Forest and off road reserves. For some quarries they have the capability of storing such water, can use it in their operations and therefore flood water is not a problem. But for many others the excessive water from off non quarry sites has been disastrous and this problem needs to be addressed.

For some in our industry dealing with water is not a problem, but for the less experienced, dealing with large amounts of water can be very daunting. This article just touches on water management of quarries and will be followed by further articles in the future.

In recent times there have been a number of incidents in both quarries and mines resulting from significant rainfall events.

The incidents resulting from the recent rains have included:

• Embankment collapses – both quarry excavations & constructed embankments i.e. dams and dumps
• Inundation of excavations
• Inundation of fixed and mobile plant
• Loss of access to plant and stockpiles

The impact of these rainfall events has been exacerbated by the preceding prolonged drought which has in many sites caused the ground to dry out and surface shrinkage cracks to form. This has allowed the recent rainfall to penetrate faster and deeper into embankments contributing to loss of their stability.

The golden rule in quarries is that unless you are dredging:

Keep Surface Water Away From Quarry Operational Areas

This is usually achieved by:

• Diversion drains
• Levees in flood plains
• Perimeter bunding
• Sumps and retention basins/dams
• Spillways on dams

The risk of incidents and the scale of the incidents will increase the further downstream you are in a given catchment. Large excavations can fi ll up in a matter of hours in heavy rainfall events and then take months to pump out.

Hydrological advice should be sought as to the size, location and construction of drains, sumps and levees to ensure they are effective. In a floodplain situation accurate level information will be required over a large area for the location and design of levees.

This can also lead to expensive hydrological modeling to convince catchment agencies that you won’t adversely impact on neighbouring properties.

Operators should also be aware of new structures such as stream crossings downstream of their site which could cause surface water to backup into their operations. This would extend to changes to drainage upstream of their sites causing increased runoff and surface flows.

It is also important to be aware of the impact groundwater can have on the stability of embankments; particularly if there is a sudden change in local groundwater levels.

The design of constructed embankments such as dams, rehabilitated slopes, overburden dumps and stockpiles is critical to ensure their stability. The proper compaction and drainage of these during construction is essential to ensure their stability and provision of safe and stable tipping areas.

The structures outlined to keep surface water away from quarry operational areas will only be effective if they are properly:

Designed, Constructed and Maintained.

They may only be needed every twenty or thirty years but their impact on human safety and the operation of your business can be very significant.

Many thanks to Basil Natoli from Bell, Cochrane & Associates for his contribution to this article.

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