Mr Jeff Seeney

[Lynette]

I heard on the radio this morning jeff asking the question. Went something like this. " What happens if when you build the dam to its full height and we have a dirty great flood. How will the water get away?" I think he was asking Henry. Not sure.

That is right. What they are going to actually do is build an OBSTRUCTION across our river with a narrow outlet for overflow. What happens when the mighty Mary roars as we know she can and has done? And overnight!!!

What happens to the people in the second stage that will still be there? The last big flood we had was frighteningly close and we are one of the little bits sticking out.

I cannot believe I never thought of it like that. Burnout I think.

[westholme]

I asked this exact question (one on one) of the NRM guy at the Amamoor landholders forum. His answer did not take into account what I was telling him. He described the spillway design and the deep pool design and he still wouldn't comprehend the enormity of floodwaters in our mighty catchment. If the dam is full I cannot see how the dam wall can accommodate the volumes of water running out of the hills, gullies and mountains.
I liken it to putting a 2 inch poly pipe into a trough with a 3/4 inch outlet. Doesn't matter how well built it is, theres more water running in than going out. The dam will overfill and overflow, I have no doubt of that. If it won't, well, I'm no engineer and clearly some things are beyond me.

[stevem]

Lynette that is a very valid question.

My property is about 600 metres away from the exclusion zone and will be surrounded on three sides when stage 3 is completed. In the 1999 flood my back acreage went under water. I have asked the question what will happen when there is a great big wall slowing the natural flow of retreating floodwaters?

Looks like my tinny will be getting a little bit more use then previously bargained on.

[Darren E]

Lynette,
Jeff is asking the right questions.
I saw Beattie on TV last night saying "the water level will never go over 71m". But he has clearly described the 79.5m level as a "flood buffer". And during the high flow of a flood event, the back end of the dam will likely be a few metres over that level for a few days (due to the water gradient).
Sorry, I know that must be depressing news.

[Lynette]

Stevern maybe everybody in stage 3 should demand a tinny, floaties and flippers be included in the compensation. Or maybe pb can give a guarantee that nobody will drown.

Did a search on google long time ago for the highest depth of water to go over a dam wall when full in a flood. Forgotten the freaky number of mtrs and now google refuses to come up with the answer again. Found this when I was looking though








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A Safe Dam - A Sure Supply: The Warragamba Dam Auxiliary Spillway

Warragamba Dam
Warragamba Dam is vital
Water is a precious natural resource. We all rely on a safe and secure water supply. This is especially important in the nation’s most densely populated area - the greater Sydney region.

Lake Burragorang, formed by Warragamba Dam, holds 80 per cent of Sydney’s available water. This is equal to about four times the volume of Sydney Harbour.

Households, business and industry all need a secure water supply and Warragamba Dam plays a vital role in meeting this need for the greater Sydney region.

Planning for extreme floods

Warragamba Dam is the largest concrete dam in Australia. Since completion in 1960, regular reviews consistently confirm the dam as structurally sound.

But new developments in rainfall and flood estimation show that Warragamba Dam could experience floods much larger than previously predicted.

Warragamba Dam was designed and built to withstand floods with a one chance in 700 (1:700) of happening in any year. In fact, the largest flood on record in the Hawkesbury-Nepean River, in 1867, had odds of just one in 200 (1:200).

In 1985, a panel of international dam safety experts confirmed Sydney Water’s findings that Warragamba Dam’s ability to safely handle rare and extreme floods was below modern dam safety standards.

As it was, if such rare and extreme floods occurred, the volume and power of the floodwaters would ‘overtop’ the dam. Sections of the wall would collapse, releasing most of the stored water.

What would happen if the dam were to break?

A collapse of Warragamba Dam would have critical social, environmental and economic consequences.

Prior to dambreak, the Hawkesbury-Nepean valley, including the population centres of Penrith, Emu Plains, Richmond and Windsor would experience very serious flooding. Dambreak would flood around 4,000 houses and irreparably damage 6,400 more, leaving over 20,000 people homeless.

Severe water restrictions, unprecedented since the 1934-42 record drought, would be imposed while the dam was rebuilt. This process would take around five years, with a further three to five years for the lake to refill.

Dambreak flooding would cause an estimated $4.5 billion damage.

Ensuring Warragamba’s safety

Warragamba Dam must meet current international dam safety standards. It must also satisfy the NSW Dams Safety Committee, the State’s regulator. Because the dam supplies the majority of Sydney’s residents with drinking water, safety is a top priority.

To protect the dam, a second spillway was constructed to divert excess floodwaters around the dam. This will reduce the pressure on the dam wall and protect it in the event of an extreme flood.

Begun in late 1998, the $150 million spillway was completed in June 2002.

Initial dam safety works

Following the 1985 review of Warragamba Dam’s extreme flood capability, Sydney Water acted quickly to further improve the dam’s safety.

As an urgent first step, the dam wall was raised by five metres and strengthened by installing post-tensioned steel cables, effectively tying the upper part of the wall to its base.

These measures cost $29 million and lifted the safety level from 50 per cent to 75 per cent of the required standard.

Long-term safety options

A range of further improvements to dam safety was considered before the current, second spillway option was selected. These included:

increasing flow through the existing spillway
allowing a strengthened wall to be overtopped
temporarily detaining the excess flow upstream
diverting the excess flow around the dam, and
combinations of the above.
The various options were evaluated against the following criteria:

effectiveness in reducing the risk of dam failure
environmental impacts, and
cost.
Preferred option - auxiliary spillway

The plan to divert excess floodwaters around the dam through a second spillway, located on the east bank of the Warragamba Gorge, was selected as the preferred option.

The auxiliary spillway will ensure that the dam is 100 per cent compliant with the required safety standards.

Spillway benefits

The Spillway will:

prevent dambreak in extreme floods
protect Sydney’s major water supply
reduce risk of dambreak flooding
reduce potential flood levels at Windsor by up to four metres
be the most practical and cost-effective way to increase flood handling capacity
enable the dam to fully comply with modern dam safety standards
prevent an estimated $4.5 billion in damages
employed up to 175 construction workers during building
created additional off-site employment through production and supply of construction materials and equipment, and
stimulated the NSW economy with up to $160 million in flow-on effects.
Impacts of the spillway project

Like any project of this size, building and operating the auxiliary spillway has some local impacts.

All likely impacts of the construction and operation of the auxiliary spillway, including measures to ease those effects, were comprehensively detailed in an Environmental Impact Statement (EIS) undertaken by Sydney Water. (The spillway project began under Sydney Water but was transferred to the SCA along with ownership of all the dams in 1999). All likely impacts on threatened flora and fauna were addressed in a Species Impact Statement, a complementary document to the EIS.

Following approval from the NSW Minister for Urban Affairs and Planning, Sydney Water decided to proceed with the construction of the auxiliary spillway. In response to comments received after the public exhibition of the EIS, some changes were made.

How the auxiliary spillway will work

Warragamba Dam’s existing crest gates and central spillway will continue to manage the normal discharge of floodwaters.

In the event of an extreme flood, a series of erodible earth and clay walls or “fuse plugs” built across the upstream opening of the auxiliary spillway progressively wash away by the rising floodwaters. The auxiliary spillway then diverts excess floodwater around the dam. The “flip bucket” at the downstream end of the new spillway manages the floodwaters entering the river at the point where they, and the flow from the existing central spillway, meet. This minimises erosion of the riverbed and banks.

The auxiliary spillway operates only in the event of a flood with one chance in 750 of happening in any year. This is more than three and a half times less likely to occur than the record flood of 1867, which had one chance in 200.

Building the auxiliary spillway

The spillway was designed by the NSW Department of Commerce and built by Abigroup Contractors Pty. Ltd., a major Australian civil construction company. The project was managed by Australian Water Technologies Pty. Ltd.

Community and environmental concerns

Before work started, a rigorous process was set up to ensure all community and environmental issues were properly dealt with during project planning, construction and restoration stages.

An independently chaired Community Liaison Committee was established to exchange information with the local community and resolve issues affecting residents.

A comprehensive Environmental Management Plan was prepared and an Independent Environmental Management Representative appointed to ensure compliance with all environmental regulations and the NSW Environment Protection Authority requirements.

Construction and rehabilitation

Construction involved excavating 4.3 million tonnes of rock from around the eastern side of the dam. This created a channel some 700 metres long, 190 metres wide at the upstream end, 65 metres wide at the down stream end and with a maximum depth of 50 metres.

The excavated spoil (rock and soil) was removed by large off-road haulage vehicles, transported across the dam and placed on land on the western side of the dam. The disposal site contains erosion control measures and is being progressively landscaped and revegetated using native species.

The spillway is lined with concrete and features a dam access bridge. A series of earth and clay walls or “fuse plugs” approximately 14 metres high are installed across the upstream opening of the spillway.

The project also involves some extra works including modifications to the crest gates on the existing central spillway, further strengthening of the existing spillway training walls, and construction of a bulkhead wall around the valve house.

Heritage items

Construction of the spillway involved the removal of much of the overhead cableway across the Warragamba Gorge - specifically the head tower and lower tail tower, located directly in the path of the spillway and spoil haulage road.

The cableway played a unique and significant role in building Warragamba Dam and a number of initiatives are being undertaken to preserve its heritage significance.

The heritage significance of all items affected by the project is fully documented, including comprehensive photographic records.

Picnic areas

Haviland Park, the picnic area immediately next to the dam, is temporarily closed to the public. This recreational area will be restored, attractively landscaped and refitted with improved visitor facilities and an information centre prior to reopening.

A safe dam - a sure supply

The raising of Warragamba Dam by five metres, the installation of post-tensioned steel cables and the construction of the auxiliary spillway, collectively ensures the security of Sydney’s major water supply and protects downstream communities from the risk of dambreak flooding.





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ugh.

[elaine]

I think another point that we need to hammer at - ask questions of whoever you can - is to do with the effectiveness of the smaller 'saddle dams' that are now being shown as part of Henry's 'Sim City Dam Model' that was shown to the Estimates Committee yesterday. 'Gympie Times' had part of the pic on the front page of today's paper, showing a saddle dam on properties on the east side of Frayne Rd (on first appearance, it would seem that this diagram may be shown in the wrong place. That's what happens when you rely on desk-top studies that pay no respect to actual reality). There are probably another 3 or 4 of them planned for elsewher in the Valley. These would appear to be even higher structures than the main dam wall. No mention of these has been made before, and there's a lot of questions to be asked about them (placement, height, structure, etc etc).

[westholme]

Could you explain a saddle dam to me please Elaine?
I've looked at the Gympie Times site and they didn't have a front page picture like they have done in the past. When you say east of Frayne Rd, do you mean up our valley here on Frayne Rd, or do you mean on the other side of theroad from the Frayne Rd turn off?

[Darren E]

Saddle dam. Shaped like a saddle. Higher at each end than in the middle.

[Scott Thomson]

As a general rule in the past dams have made floods worse not better. They store the water till they cannot hod any more then they have to open the flood gates to prevent the wall being damaged. This releases megatonnes of water instantly downstream from the dam causing massive instant flooding.

So yeah I would be concerned about that issue too.

Cheers, Scott
_________________
Scott Thomson
Carettochelys.com
Skype Id: Faendalimas

[kevin.coppalotti]

The whole idea of stage 1 and stage 2 was a diversionary tactic to divide and conquer the dam opponents. The concept of 1000 drizabone clad horsemen swarming down from hills would be be to much for Beattie to bear.
So, this is his 'whatever it takes' strategy. He will just wait for the stage 2 people to swim to shore in the next flood, give them a set of dry clothes and $50 worth of food stamps and say "I'm sorry....BUT.."
Anyone who trusts these lying lowlife scoundrels has rocks in their head.
_________________
Kevin.coppalotti. www.razorsharp.smugmug.com
http://maxhr.zenfolio.com

[elaine]

In answer to westholme's earlier question, the 'Gympie Times' front page pic has a saddle dam on the east side of the Frayne Rd valley, so it is just upstream of the main dam wall.

[stuffthedamthing]

The saddle is to prevent an overflow when the dam is at full supply level or when it floods.
My opinion is these guys don’t know what they are talking about + they are unaware of the topography of the place.
If you see the map on the Gympie times the position of this saddle, is right under the mango orchard on the left as you enter in Frayne road.
I don't want to be an alarmist. But...
Unless the FSL is going to be higher then we have been told.
Then again; if it is to scale, it appears like a wall structure on the side of the hill. It doesn’t make any sense.

[SteveB]

Went down to look at the site of the proposed saddle dam on Frayne Rd this morning.

Either the drawing is wrong and they meant to have it a lot further down Frayne road where it dips down low, or they are worrying about a water level much higher than 79.5 metres. By my reckoning, the saddle dam would be about 90m above sea level if the location on the map is correct.

Happened to run into Mick Vernardos by accident and we spent some time looking at the air photo and map - it was the first he had seen of it and he was going to get the council to try and find out what is going on.

I also spent some time talking to Scott Smith about it - he claims that he had not seen these photos and drawings until this morning and was a bit taken aback when I told him that they had been published on the front page of the Gympie Times. He could not give me elevations for this saddle dam, or for any of the other saddle dams that are on the drawings (there may be 2 or 3 more needed).

My question is, if this is the height of freeboard that the engineers are suggesting will needed for flood control at the downstream end of the dam, what will the predicted flood heights be for the upstream ends of the dam? Considerably higher than 79.5 metres you can bet - the 80m countour does not need any saddle dams to stop the water from flowing where it shouldn't.

If we get any answers we will let people know.
_________________
"Bad luck ... you dickheads. Suffer in your jocks". (from: the Castle)

[Darren E]

You're right, stuffthedamthing, it makes less and less sense the more "information" they release.
According to the contour maps I've seen, the height above sea level at that location is 85 to 90 metres - well above 79.5m.
Maybe Mr Palasczcuk is saving taxpayer's money by getting the kids at his local Inala primary school to do these drawings... "who will know the difference - just make it look like we're doing something".

[stuffthedamthing]

I have worked with an altimeter al the contours in Frayne road. (I re-checked several times.)
I'm 100% sure a saddle in frayne road is not needed.
Unless the FSL is going to be higher then 79.5.
If higher than that... bye bye not only Kandanga, but the whole of Imbil as well