Wivenhoe Dam and Mt Crosby Water Treatment Plant

12 Sep

The other week we went on an awesome homeschool excursion

to Wivenhoe Dam and Mt Crosby Water Treatment Plant.

It was a very big day with lots of driving.

We arrived early so we could stop off and see the spillway gates

(which weren’t part of the official tour).
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How impressive would it be to see all 5 gates open and spilling water out into the river!

I’d love to take the boys out to see this one time.

(However, I have concerns that the roads around Spillway Common

and the carparking facilities at the lookout

wouldn’t cope well with too many sightseers and that’s a major deterrent for me.)
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I wonder how far up the water reaches when the 5 spillway gates are open.

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On the day we visited, the only water we saw running was this little tinkle,

which I assuming is just the tiny continual release that keeps the water moving and healthy.

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Of course, I positioned the boys for the mandatory ‘I’ve been there’ photo.

Don’t they look thrilled.

Okay, well it had started to rain.

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The morning certainly made us worried about the weather for the day.

It was drizzly and rather miserable looking.

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But we continued on anyway,

stopping to check out the dam wall before meeting up with our tour group.

Did you know that Wivenhoe Dam is an earth and rock embankment wall dam?

Only the spillway section is concrete.

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As you get your first view of the dam,

it’s kind of a ‘wow’ moment,

especially when you stop to think that it was once a valley

that man flooded to create a dam.

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Oh and this view shows only a very small part of the dam.

At a guess, using a map to estimate, I’d say this is about a tenth of the dam.

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That white building you can see in the distance is Wivenhoe Hydroelectric Power Station.

They pump water up from Wivenhoe Dam into Splityard Creek Dam,

and then, during peak demand,

they release the water from Splityard Creek Dam

through the turbine generators.

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Yep, more ‘stand there and smile’ family shots.

The kids just love them….NOT!

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After an hour of exploring on our own,

we met up with our homeschool group and our education guide,

who would be with us for the day.

After a discussion about the dam and why we need it,

our guide sent the children into the information centre to search for information about 5 things.

1) How long is the dam wall?

2) How high is the dam wall?

3) How does the dam operate?

4) The name of a special fish that lives in the dam

5) Why that fish is special?

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The children hunted around the centre

and discovered that the dam wall is 2.3km long and 50m high.

They watched a video about how the dam works.

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Then they found the lungfish.

(Isn’t it ugly?!  And this fella is just a baby.

On average, they grow up to about a metre in length.)

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It’s special because it has an unusual swim bladder that allows it to breath air

when it is unable to breath using its gills.

That’s kinda cool.

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After the children reported their findings,

the group headed down to the banks of the dam

to do some water quality testing.

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They received their instructions and supplies

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and then found their own locations

to begin testing.

First they collected some macro-organisms from the water

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to examine and identify.

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This little fellow is a water snail.

He’s a very tolerant fellow and is happy to live in dirty water.

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I think this fellow is our mayfly nymph

and he’s a very sensitive fellow,

who hates dirty water,

which told us that the dam water was lovely and clean.

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Once the children had finished investigating the critters,

they turned their attention to the water itself.

First, the boys tested the turbidity of the water.

Even at the top of the tube, they could still see the cross on the bottom of the tube,

which told them that the water was clear.

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Then the boys collected samples of water

added their testing tablets,

and measured the level of dissolved oxygen, the pH levels and the phosphate levels.

All of the children’s results showed that the dam water is in very good shape.

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After the water testing, our guide explained the purpose of the auxiliary spillway

which was located beside the information centre

where we had gathered.

Apparently it’s like a fuse plug.

If the water gets too high, the middle section of the auxiliary spillway

(it goes first and is then possibly followed by the others)

erodes away and releases the excess water

that threatens the integrity of the whole dam.

During the 2011 flood crisis, the dam waters were only 70cm from eroding that middle section.

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Before leaving Wivenhoe Dam, our guide showed us a Whistling Kite nest up in a tree.

A Whistling Kite is a bird of prey so, after eating, there are lots of bones and feathers and such to be disposed of.

But these birds do not drop their rubbish beneath their nest.

That would attract goannas to their babies in the nest.

Instead, the Whistling Kite takes all of their rubbish and disposes of it in the same place

away from their nest.

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Our guide took us to the Whistling Kite’s rubbish dumb

and the kids found all sorts of fascinating (gross) things.

Bones, skulls, jaws,

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and plenty of pellets

– that’s the fur or feathers that the bird of prey vomits up after a meal!

(There’s always something terribly gross to be found on my blog.)

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And how do you follow up a discussion of vomited up pellets?

With lunch of course.

We left the dam just before lunch and drove to Mt Crosby

and enjoyed lunch in a park across the road from the water treatment plant.

The tour through the Water Treatment plant was really interesting.

I mean, how often do you get to do this kind of thing.

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The rules inside the plant were quite stringent.

The children had to obey instructions immediately

and everyone had to walk inside the blue lines at all times.

(See, children don’t need 12 years of institutional schooling to learn these things.)

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How our water is treated is really quite interesting.

It’s sucked up out of the Mt Crosby Weir

(I finally understand what a weir is!)

and filtered through this big brown ‘inlet screen’.

There are two.  One is in use while the other is cleaned.

These filters catch the really big stuff – leaves, twigs etc.

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The first stage in the water treatment process

involves adjusting the pH levels by adding Caustic Soda

(if necessary; and in order to help the next process).

Then aluminum sulphate, a coagulant, is added to the water.

It makes the dirt and gunk clump together

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into what they call a ‘floc’.

Isn’t it gross?!

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As the flocs get heavier,

they sink and settle to the bottom of the sedimentation tanks.

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That lovely sludge is then ‘vacuumed’ up

by this big vacuum system that slowly rolls down the tank.

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Then water is pumped into a building

where the water is further clarified

through the process of dissolved air filtration.

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Air is released into the tanks at the bottom of the pool

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and as it rises to the top,

it brings with it even more gross stuff.

Doesn’t it look like sea foam from the beach?!

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This ‘foamy grossness’ sloshes over the end of the pool

leaving behind even cleaner water

but still not clean enough to drink.

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The remaining water is then dropped down through a sand filter

to remove any remaining impurities.

Of course, they’ve only removed the dirt and organic matter.

The water is still full of micro-organisms.

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These pipes are beneath the indoor pools

and it is down here (I think)

that the water is disinfected with chlorine,

the pH is corrected with Lime

and the fluoride is added (for our teeth).

(Later, at the water reservoir, they add Chloramine – a combo of Chlorine and Ammonia

– to make sure nothing new can grow as it travels along the pipes to our homes)

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So now the water is drinkable,

but we mustn’t forget the sludge that was removed from the water.

It is also treated.

These are sludge thickening tanks.

They add a chemical to make the sludge once again sink to the bottom,

separating it further from the wastewater.

The wastewater can then be sent back through the treatment plant

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while the remaining muddy sludge

is pumped to a centrifuge tank (hard to see in this picture)

to remove even more water

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and the almost water-free mud cakes plop out of the tank

to be scooped up and left in the drying pans

before being scattered over land.

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And that’s the process of how ‘clean’ water gets to your taps.

So what do you reckon.

Does it make you feel better or worse about what comes out of your taps?!

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(The Up A Dry Gully website has a brilliant virtual tour

of both the dam and the water treatment plants,

as well as other water-related locations.)



Posted by on September 12, 2016 in Field Trips, Science, Technology


2 responses to “Wivenhoe Dam and Mt Crosby Water Treatment Plant

  1. Amanda

    September 12, 2016 at 12:41 am

    Loved this post – although it did leave me with a sense of “ew” about drinking town water… Did you know the dam has a Wikipedia page? I just looked it up after reading your post, and there’s a 13 second video of the 5 spillway gates in use. There was also a pic in this article from the Brisbane Times just a few weeks before the 2011 flood:

  2. Petra

    September 15, 2016 at 12:41 am

    Dams are so interesting. That looked like a great excursion 🙂


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