Monday, February 26, 2007

Incidental Water Recycling at Richmond

As we have discussed previously on this blog, many communities undertake potable water reuse in an ‘unplanned’ or ‘incidental’ manner. This occurs where treated effluent from a sewage treatment plant is discharged into a waterway, which is subsequently a drinking-water source for downstream communities.

The case of the Hawkesbury-Nepean River system seems to have become a point of political disagreement in the up-coming NSW State election. So I thought it might be helpful (to all parties), to take a closer look at that particular situation. A couple of weekends ago, I placed a fresh pair of AA batteries in my ailing digital camera for a quick tour around western Sydney. This post provides a run-down of what I saw.

Click the image below for an overview of the Hawkesbury-Nepean River system.

The upper-reaches of the Nepean River extend well south of Sydney to the Southern Highlands. They include the Nepean, Avon, Cataract and Cordeaux Dams and the tributaries downstream of those dams. As the river winds north towards western Sydney, a number of sewage treatment plant (STP) discharges contribute to the overall flow, including West Camden STP.

However under current conditions, environmental flow releases from the Upper Nepean Dams (and STPs) often do not make it as far as the Wallacia Weir, which is just upstream from the Warragamba River junction. Significant wet-weather events are required in order for there to be any measurable water flow over Wallacia Weir.

For around 40 per cent of the time, the only water-flow into the river downstream of Wallacia Weir is that which is intentionally released from Warragamba Dam via the Warragamba River. The Sydney Catchment Authority is normally required to release at least 43 megalitres per day (ML/day) from Warragamba Dam to keep the Nepean flowing. However, under the current drought conditions, the interim flow release has been decreased to approximately 22 ML/day.

The first photograph below is the Nepean River perhaps 10 kilometres downstream of the Warragamba River junction. The view from ‘The Rock’ lookout near Mulgoa is spectacular and the silence is eerie. Practically all of this water has been released from Warragamba Dam and it moves very slowly along the valley floor. However, a large rain event a week earlier appears to have washed a considerable load of mud and silt from the upper river reaches. This shot is looking North East, downstream towards Penrith.

Between the junction of Warragamba River and Penrith Weir, the Nepean River receives inflow from a number of tributaries and surrounding catchment. One of the best-known views of the Nepean River is that from the Nepean Rowing Club, beside the Victoria Bridge. This photo was taken from the boat ramp behind the club and is facing back upstream towards Warragamba.

A few hundred meters downstream from the Nepean Rowing Club is Penrith Weir. The weir helps to maintain stable volume upstream. It was built in 1909 to provide Penrith with a permanent water supply. The weir forms a long pool on the upstream side of it, which extends for a distance of around 18 km and holds around 6000 ML of water. Dry weather flow releases from Warragamba Dam typically have a residence time in the weir pool of around 6 months.

Approximately 62 ML/day flows over Penrith Weir under very low flow conditions (95th percentile). Under median flow conditions (50th percentile) approximately 146 ML/day flows over Penrith Weir.

Not shown in this picture is the innovative ‘fish ladder’, which allows migratory fish to swim upstream, around the side of the weir.

Another significant source of water to the Nepean River is the Penrith Sewage Treatment Plant (STP). This plant has a dry-weather flow rate of around 22 ML/day.

Treated effluent from the Penrith STP is discharged into Boundary Creek, which is a small creak that runs along the side of the plant. As you may be able to see from the submerged reeds in the photograph below, this is a particularly fast flowing creek.

Boundary Creek flows towards the Nepean River, which it meets about 500 metres from the Penrith STP. Boundary Creek joins the Nepean about 50 metres downstream of Penrith Weir. This shot shows the creek as it is about to arrive at the river.

Here is the actual point of confluence of Boundary Creek and the Nepean River. While the volume coming from Boundary Creek is relatively constant, the relative mixing ratio is quite variable since the volume flowing over Penrith Weir is variable.

Regardless of the additional influx of water from Boundary Creek, the water depth decreases markedly downstream of Penrith Weir.

As we go further downstream, this area around Emu Plains is particularly degraded and suffers from a lack of water flow. The river reach has been significantly modified due to sand and gravel mining, producing artificial low flow velocities, which has impacted on habitat conditions. As can be seen in the photograph below, the water is highly laden with silt and numerous small islands have been formed and stabilised with trees.

This next picture is more than 10 kilometres north, taken from the end of Coolamon Road at Agnes Banks. Sadly, its quite difficult to find public access points to the river between Penrith and this point. Apart from the river banks themselves, much of the land on either side is privately owned with very few public thoroughfares. It is along this stretch of the river that another small waterway meets it from the western side. This waterway carries an additional 15 ML/day of treated sewage effluent from Winmalee STP in the lower Blue Mountains.

The river is, of course, an important source of irrigation water for many of the farms. From what I can tell, the major farming industries appear to be turf farms, citrus farms, horse studs and beef cattle studs. I couldn’t actually tell what was being irrigated in the photograph below. It appeared to be a weed farm, but was probably something more valuable.

The character of the river changes quite a bit around Yarramundi. The river narrows and the bed becomes quite pebbly. This is another major zone of the river that has been affected by in-stream gravel extraction, which occurred here between 1927 and 1989. The narrower river means that the water flows noticeably more quickly along these stretches, even during periods of relatively low flow.

The view from beneath the Yarramundi Bridge provides an instant indication of the variability of water flow along this stretch of the river.

The shot below was taken from the Yarramundi Bridge facing north. This seems to be about the point at which people stop calling it the Nepean River and start calling it the Hawkesbury River. Just around the bend to the left is the junction with the Grose River (see the next photo).

The only significant waterway to meet the river between Penrith and Richmond, which is not predominantly comprised of treated effluent is the Grose River. The Grose River is a rather underwhelming waterway, especially if it hasn’t rained in the last couple of days. In many places, the water is ankle-deep, tea-coloured and rather stagnant. A large rain event, which occurred a week prior to the below photograph deposited a large amount of silt in the lower reaches of the river. This photo is taken from Navua Reserve, a few hundred meters upstream from the Hawkesbury. In low flow conditions, the Grose River contributes around 60 ML/day.

Here we have the Richmond Bridge over the Hawkesbury River. This photo is of the southern side of the bridge looking from the western bank towards the eastern bank. It is the site of the first bridge built across the Hawkesbury. A timber bridge was built here in 1860 by the Richmond Bridge Company. The present 214 m structure was opened in 1905 and was Australia’s largest reinforced concrete bridge for over 25 years. Later widened in steel, it carried the railway extension to Kurrajong from 1926 until 1952.

It is at about this point that the river becomes tidal. In fact, when I took this photograph, the surface of the river was flowing southward (ie. back towards Penrith). I thought this was a particularly interesting observation since a number of significant sewage treatment plants (eg St Marys STP and Quakers Hill STP) discharge treated effluent into waterways that join the Hawkesbury River further downstream. In fact, the North Richmond STP discharges into the Hawkesbury little more than a kilometre downstream of the bridge. It seems inevitable that some of this water may then be pushed back to Richmond by rising tides, before subsequently being released north again by falling tides.

Roughly a kilometre upstream of the Richmond Bridge is an intake for the North Richmond Water Filtration Plant, which is owned by Sydney Water. The plant treats up to 50 ML/day by filtration through granular activated carbon and chlorine disinfection.

After treatment, the water is stored in this reservoir in preparation for reticulation. It is supplied as high-quality drinking water to 16,000 lots in the Hawkesbury region, including North Richmond, Richmond, Toorah, South Windsor, Pitt Town, Wilberforce, Kurrajong and Glossodia.

Of course, the Hawkesbury-Nepean doesn’t stop at the North Richmond Water Filtration Plant, and supplying drinking water is not its only important function. Many stretches of the river are astoundingly beautiful and, in my opinion, widely underappreciated by Sydneysiders. We have a responsibility to maintain a high water quality in the river and –very importantly- a healthy flow of water. The significant water flow is essential to keep it moving, keep it oxygenated, prevent the build-up of silt, prevent stagnation and provide an attractive habitat for native fish.

I hope you enjoyed the journey. Perhaps we’ll do the Murray River next time!

PS. I received a question from a commenter with the pseudonym ‘Interested’, who wanted to know about the ‘innovative fish ladder’, as I referred to it. Well, it looked fairly innovative to me, but a quick Google search suggests that the consensus is that it is relatively ineffectual. It is reportedly designed for trout (so that they may swim upstream). But apparently fish passage “is hindered through its design and detached aquatic vegetation and debris blocking the upstream entrance”. It certainly didn’t look blocked the day I visited, but perhaps it had recently been maintained (and of course, I couldn’t see what was below the water surface!) Here’s what it looks like:


interested said...

What does the "innovative fish ladder" at Penrith Wier look like and how does it work?

Stuart Khan said...

Hello Interested,

I’ve now added a picture of the fish ladder to the end of the post. Does anybody here know more about how they (are supposed to) work than I do (which is practically nothing)? Obviously they provide a gradual water gradient for the fish to swim up, but how do they handle variations in water flow?

Alexandra Golab said...

Hi Stuart,

Thanks for the informative look at Indirect Potable Reuse on the Hawkesbury Nepean. I would indeed be very interested to see something similar for the Murray.

Good luck with the conference.


Stuart Khan said...

Thankyou Alexandra,

As a resident of Canberra, perhaps I could begin at your kitchen sink and we could follow the water via the STP back into the Molonglo River, joining up with the Murrumbidgee before reaching the Murray. After a short stop-over in Mildura, we would make our way to various drinking water filtration plants in and around Adelaide. Maybe not this weekend...

Anonymous said...

Stuart, Why begin at Alexandrias kitchen sink? Why not her toilet???

Stuart Khan said...

Fair call, Anonymous. We’ll start at Alexandra’s toilet. I hope that with a bit of advanced notice she will have it looking respectable for camera.

Anonymous said...

It would be better if she didn’t clean it for the cameras. That would give a more honest representation of what actually goes into the toilet.

Stuart Khan said...

Okay. No advance warning, Alexandra.
However, if her toilet is anything like her desk, its bound to be unrepresentatively spotless anyway.

alice said...

That's an excellent work on your part Stuart, Thanks for the History of Nepean - Hawkesberry river - for a person, unaware of the River histories in Austalia !!!!

Anonymous said...

Great blog. I enjoyed the feild-trip!

Anonymous said...


I am a engineering equipment supplier and I would like to have the opportunity to introduce my product range to the different waste water treatment plants in the Sydney metropolitan area.

My company is called Stauffpumps and if you could provide to me the list of the treatment plants with contact details.

I greatly appreciate it if you could assist me.

Carlos Gonzalez
(02) 8787 1400

Leonard said...

Stuart, that was an interesting tour of the Hawkesbury-Nepean indicting the location of STPs a WTP, weirs, a fishway etc. We are happy to hear that NSW government has diversified, water industry from depending on dams only, to dams+ recycling+ desalination+ water efficiency.

Now a comment about fishways. Fishways in NSW have been built for the migration of native fish (not for trout). The native fish populations in the Hawkesbury-Nepean consist of fish species that migrate to the sea from the freshwater (catadromous: e.g. Australian bass) and vice versa (anadromous: e.g.Australian grayling) for spawning. Some other species move extensively in the freshwater system and others between freshwater and sea, though not for breeding. So, Aussie fish are great travellers. Hence, the fishways are expected to increase biodiversity and enhance recreational fishery.

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