Harvesting Water

The numerous granite outcrops throughout Western Australia’s agricultural regions are a valuable source of water if the runoff can be captured or ‘harvested’.

Many of these granite outcrops, particularly eastward towards Kalgoorlie and beyond, have had low walls, typically 300-500mm high, erected on a selected contour of the outcrop that channels water flow into another channel or a culvert and ultimately into a reservoir or tank located lower down the rock. Many of these reservoirs were roofed to slow down evaporation.

: Uprights are all that remains of the means to reduce evaporation. The reservoir was roofed.

The harvest walls that aggregate water from the rock and the channels that then direct the precious liquid into a tank or dam are invariably fine examples of stonemasonary.

Wave Rock (more correctly Hyden Rock) is probably the most famous rock to be harvested. Clever photographers avoid including the wall at the top of the wave in their photographs.

: A fine example of a harvest wall. This is at Cardunia Rocks.

Water harvesting and collection in tanks was often for community water supplies but the most common use was for the boilers on steam trains.

The amount of water harvested from a granite outcrop depends on the size, steepness and shape of the rock. Estimates of runoff at, for example, Karalee Rock are that a 25mm/hour downfall would have a runoff of 6200L per acre.

Reference
Laing, I.A.F. and Hauck, E.J., Water harvesting from granite outcrops in Western Australia, Journal of the Royal Society of Western Australia, 80: 181-184, 1997.

© Kim Epton 2019-2024
292 words, two photographs.

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Boab Trees

Boab trees are of the genus Adansonia. In Africa and Madagascar these trees are known as baobab. The Australian species Adansonia gregorii (named in honour of explorer Augustus Gregory) has been evolving for 190 million years. They are thought to have originated from plants washed ashore from Madagascar, although this is not universally accepted. They are now considered to be native to Western Australia.

It is sometimes claimed that the boab is the oldest living thing in Australia. But – stromatolites!

: The famous Gregory Tree near Timber Creek.

Boab trees grow to a height of 15 metres although 9-12 metres is more usual. The drop their leaves during the dry winter of northern Australia. These trees are found throughout the Kimberley, extending into the Northern Territory.

© Kim Epton 2021-2024
161 words, one photograph.

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Man in the Moon Crater

Shoemaker Crater is about 100 kilometres north-east of Wiluna.

This impact crater was formed some time between 500mya and 1.6bya, depending on which source you believe. At that time there were no plants, no animals and no fungi – only stromatolites. A very different planet from today. A 2600 metres wide asteroid hit outback Western Australia at a speed of 65,000 kilometres per hour, creating a 30 kilometres wide impact that was identified as an impact crater in 1974.

: At the centre of Shoemaker Crater.

It is estimated that the resulting explosion was the equivalent of 784 megatons (about 15 x larger than Tsar Bomba – the largest nuclear bomb ever detonated) and generated an 8.5 magnitude earthquake. The heat and thermal radiation would have destroyed any lifeforms for a 500 kilometre radius.

The crater was named after Eugene Shoemaker (1928-1997) a renowned US planetary geologist who was killed in a vehicle crash on the Tanami Track in the Northern Territory. His ashes were on the Lunar Prospector when it was deliberately crashed into Mawson Crater near the South Pole of the moon in July 1999. The International Astronomical Union then renamed the crater as Shoemaker Crater.

: Eugene Shoemaker

© Kim Epton 2022-2024
219 words, one photograph.

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Breakaways

Breakaways are a notable feature of inland Western Australia. In what is one of the oldest geographical regions on Earth, the Yilgarn Block, softer soils have gradually eroded through the repeated action of wind and water. Only those areas with a hard laterite (ironstone/granite) top have resisted this reshaping erosion.

Where the crust of these laterite layers has crumbled the hard top remains to form a ‘mesa’ while the continuing erosion of the surrounding softer soil and rock forms a steep ‘breakaway’.

The magnificent colours often seen in breakaways are a consequence of varying soil types with laterites giving the rusty reds and shales and sandstones the softer yellows and whites.

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Shipping Containers Disguised as Water Tanks

Travel any distance in the bush and you will come across one of more of these cube-shaped, rivetted iron water tanks.

: A ship’s container repurposed as a water tank. Ubiquitous throughout the bush.

However, they are not a purpose built water tank but were originally a ships’ tank used for transport of many varied items – the precursor to today’s ubiquitous shipping container.

Early settlers immediately saw the advantages of their size and sturdy construction, repurposing them as water tanks.

More information

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