Perth’s flooded gum

the boardwalk at Lake Gwelup wends through Eucalyptus rudis

The flooded gum (Eucalyptus rudis) is Perth’s river gum, growing along our rivers, lakes and water courses. Its range extends north to Geraldton and into the south-west of WA. These beautiful trees surround Lake Gwelup and as the water level ebbs and flows, they often stand in water in winter and spring. With this inundation from winter rains they flower and this month the first flowers are starting to open.

bud caps of Eucalyptus rudis with first flowers of the season

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world oceans day

don't let the sun set on our seas

Today is World Oceans Day. Our oceans cover 70% of the Earth’s surface and hold most of our water, but they are threatened on many fronts and need our help. Climate change is slowing but surely killing coral reefs.

“The magnificent Great Barrier Reef is already experiencing severe bleaching due to a 0.4°C rise in water temperature. Each year, about 60% of our reef is subject to some bleaching. Professor Ross Garnaut pointed out that we are ‘likely to see, by mid-century, the effective destruction of the Great Barrier Reef'” – Australian Conservation Foundation

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a glass of rainwater

glass of rainwater

I’m drinking rainwater again after 6 months of tap water. After my tank ran down over summer, I didn’t set up the filter again until now. Why did I take so long when my favourite drink is rainwater??

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Perth’s shrinking Groundwater

Most of Perth’s water comes from the Gnangara groundwater mound (aquifer), stretching from north of Perth to the Swan River, as far south as Fremantle.

The Gnangara Mound is an important source of water for public water supply, irrigated agriculture, parks and gardens, industry and groundwater dependent ecosystems. Groundwater levels across the Gnangara Mound have generally been in decline for the last thirty years. This coincides with a general trend of declining annual rainfall across the south west of Western Australia. [1]

decreasing groundwater levels across the Gnangara Mound
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Desalination in Cockburn Sound

A month ago the Perth Seawater Desalination Plant in outer suburban Kwinana had to cut its production (from 130 million litres of drinking water a day to just over 21 million litres) for about a week because low levels of oxygen were measured in Cockburn Sound [1].

Cockburn Sound The saltwater outlet of the plant is located in Cockburn Sound, a sheltered bay with marine life feeding grounds in seagrass meadows which are under ecological stress from industry on the Sound [2]. The outlet was not in the open ocean where water movement would disperse the hypersaline water faster, because the cost of a pipeline that far was considered too expensive. Two detailed field experiments were conducted under calm conditions (when oxygen levels are lowest) by the UWA Centre for Water Research and found that the hypersaline outlet is not effecting the environment of Cockburn Sound.

The combination of experimental and numerical modelling results demonstrate that the saline discharge is diluted to such an extent by the action of the diffuser and natural environmental mixing processes that the Perth Seawater Desalination Plant has no measurable impact on the oxygen levels in Cockburn Sound [3].

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A year of solar water heating

Hot water accounts for more than 30% of energy used in the home. [1]

the solar water heater on my roof I’ve had solar water heating for a year. I wanted a gas booster, rather than the electric booster which was installed. My dad (who is my landlord) has had bad experiences with a gas booster, so he didn’t get one. He also told me that the person who installed the system said electric boosters are better, but I wonder if that’s just what the installer likes, or something.

A brochure from the gas company said (admittedly this may be biased because gas it what they sell)

Solar power systems are the most energy efficient if you choose a gas-boosted system. Electric boosted solar systems emit nearly the same amount of CO2 as hot water systems which run [solely] on gas. [1]

From February last year when the system was installed, the booster wasn’t turned on until winter. The weather usually breaks in May in Perth, but April last year was very wet, so the booster was probably used then. June was very dry, so I think it would have been turned off for a lot of that month.

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Swales Saving Water

Every now and then I borrow The Earth Garden Water Book from the library and dream about the things I could do if I had a block of land. A few months ago I did this and came across swales. I loved the sound of the word and decided I wanted a swale. Unfortunately I read a bit further and discovered a swale is a ditch that follows a contour and catches water which would otherwise just run down the contour and be lost [1]. My small, flat garden won’t be getting a swale any time soon.

Kirsten and Nick at Planting Milkwood have got past the dreaming stage and have designed water into the landscape of their property. This week Geoff Lawton is teaching a three day earthworks course at Milkwood to construct the necessary dams, swales, etc. in order to

harvest that water and divert it across the landscape so that it seeps in gently and slowly, creating places for things to grow, rather than have the water pelting down the cleared gullies on either side of Milkwood, to swell the eroded creek and rush off downstream before the land and the soil has had a chance to benefit from it.

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Drinking Rain

Of course we all drink rain, one way or another. The water cycle eventually recycles all water into the sky and then back down to the earth, but some people drink their water a bit closer to when it fell as rain, than others. Sadly I’m not one of these people, but I look forward to the time when I have a rainwater tank.

the water cycle by John M. Evans, USGS, Colorado District

I just came across Greenfoot’s blog and her question about Sustainable House Day. Georgie commented on the Australia Street house in Newtown, Sydney.

The house incorporates all manner of sustainable features, including a ventilation stack and a low-tox or no-tox approach to paints and glues throughout. It also features a pool: a decadent, gorgeous plunge pool, tucked in a corner of the courtyard next to the living area, filled entirely by water from the house’s rainwater tank. [1]

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Rain, Rain, Rain

After Perth’s lack of rain in June (60mm compared to the previous average of 139.6mm*) Perth was facing a lower than average rainfall for July.

This map from the Australian Bureau of Meteorology shows the areas of Australia which experienced serious to severe rainfall deficiencies from 1 July 2006 to 30 June 2007. Perth is in the palest pink area, with a serious deficiency in rainfall. Rainfall in Australia July 2006-June 2007

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Winter in Perth

It’s been a very dry start to winter in Perth this year. I usually don’t have to water my garden at all from sometime in May on, but in the last two weeks I’ve been watering my vegies every couple of days.

The average rainfall for June in Perth is 139.6mm from the Bureau of Meteorology. If we’re going to get anywhere near the June average its going to have to rain an awful lot in the next ten days, because so far we’ve had 9.2mm on only four June days. Rain is forecast tomorrow and for the following week, so it might happen.

Perth’s winter rain usually starts in May. In May 2007 there was 61.4mm of rain and this only fell on thirteen days of the month. This is compared to the average for May of 91.5mm.

Australia is prone to drought and the El Niño event of the 2006/07 summer caused a severe drought. Some areas of Australia received above average rainfall in autumn and this has caused some relief. Other areas have ended the drought with too much rain. New South Wales is about to experience their third major storm this month.

The storms that hit the Hunter Valley region and the Central Coast several weeks ago left nine people dead and a clean-up bill that is already running into the hundreds of millions of dollars.

Rainfall in Australia March-May 2007
This map of the past three months rainfall in Australia is for rain in Autumn and the west of Western Australia is mainly pink and red, with lower than average rainfall. Perth is in a white area (average rainfall) because the lower rainfalls of March 6.2mm and May were added to April’s rainfall of more than double the average amount at 76.4mm. This high monthly rainfall was caused by one day when 40mm of rain fell, more than April’s monthly average.

Perhaps this means Perth’s rainfall has just gone a bit wonky.

NB. I mentioned El Niño above, but it affects eastern and western Australia differently. While it’s often linked to reduced rainfall in eastern and northern Australia; Western Australia, not being on the Pacific Ocean, won’t necessarily experience drought at the same time. El Niño is a natural phenomenon which is separate to human induced climate change, although the severity of El Niño events might be affected by climate change.

A few years ago I read a book called El Niño: The Weather Phenomenon that Changed the World by Ross Couper-Johnston (2000, Hodder & Stoughton). It describes El Niño events through history (determined by looking at historical weather events, etc.) and the differences between El Niño and its opposite La Niña, which (I have a vague recollection) causes more problems for Western Australia. Maybe I need to look at it again to fix that vagueness.