Lower Kowmung River to be Destroyed!!

[DaveNoble]

The state government is going to announce the raising of the wall of Warragamba Dam by 14 m today for flood mitigation. So far on the news reports I have heard nothing about the destruction of a world heritage area. This will destroy the Kowmung River. For more information see - http://www.dontraisethedam.com. Here is one news report - http://www.smh.com.au/nsw/warragamba-dam-wall-to-be-raised-to-avoid-catastrophic-flood-event-20160616-gpkqly.html

This is very bad news.

Dave

[robl]

Perhaps the extra 14m will only be used for flood mitigation in that rare 1 in 500 year flood and will only be needed for a day or so.
Is the capacity going to be increased? My reading is that it is for flood mitigation only.
Interestingly they have just finished spillway work in the last few years to prevent wall failure for 1 in 700 year floods. (if I remember correctly.)

[jackattack]

I read this online today as well. Have not had the pleasure of seeing the Kowmung yet. What fence to I need to chain myself too? What I am really asking is what can be done, which group is best to work with?

[ribuck]

...they have just finished spillway work in the last few years to prevent wall failure for 1 in 700 year floods

Does this mean that each year there is a one-in-701 chance that the dam will fail? Are there any statisticians here who can interpret this?

[GPSGuided]

Perhaps the extra 14m will only be used for flood mitigation in that rare 1 in 500 year flood and will only be needed for a day or so.
Is the capacity going to be increased? My reading is that it is for flood mitigation only.
Interestingly they have just finished spillway work in the last few years to prevent wall failure for 1 in 700 year floods. (if I remember correctly.)

+1

What I heard too. The extra 14m is going to be for times of extreme rain to avoid spilling. Nothing mentioned about raising the storage level.

[Tyreless]

The Colong Foundation has some information - see the link in the first post. But it is based on a 23m increase in wall height, not a 14m increase. My understanding is that the concern relates to impacts arising when the higher wall is used for flood mitigation purposes and whether the areas then flooded will ever recover.

I'd like to see the "other side of the story" and find out what those impacts are, how often they occur, and whether they can be mitigated. Unfortunately, my google searches drew a blank. I am concerned about an anouncement of this sort of work if there is nothing published to back it up,

[GPSGuided]

The SMH reported that,

The Hawkesbury-Nepean Valley between Penrith and Sackville has the greatest flood risk of anywhere in NSW.
The government says up to 134,000 people who live and work there could require evacuation in the event of a large flood – a figure forecast to double in the next 30 years.
In 2012, Infrastructure NSW said a study it commissioned found that a one-in-1000-year flood in the area similar to the 2011 Queensland flood would cause damage estimated at $8 billion.
This included potentially putting 43,000 residents and 9000 local employees at risk, destroying 6500 homes and flooding 14,000 homes above floor level.

So there must be a completed technical analysis on this issue somewhere. Still, no mention that the managing authority wants to raise the normal water level but to assure control and safety at times of catastrophic flood. We need to see the environmental impact review on this before claiming assured destruction.

[davidf]

I have spent time in the zone. Damming absolutley destroys an area. When water is high it is beautiful. When water is low you get a muddy smelly mess. The creeks that already meet the Coxes into the catchment in anything but flood are foul. To think that the kowmung/coxes junction could suffer this is horrible.

I can handle the dogs, pelicans and horses living down stream but this must stop.

[GPSGuided]

What's the ASL for Kowmung/Coxes junction and what's the ASL of said dam?

This article has more convincing information.
http://www.dontraisethedam.com/raising- ... hwalker-38

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[Allchin09]

What's the ASL for Kowmung/Coxes junction and what's the ASL of said dam?

This article has more convincing information.
http://www.dontraisethedam.com/raising- ... hwalker-38

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I believe that the junction is the same elevation as the dam stored water mark

[GPSGuided]

Ummm... That'd be problem. Then the junction is already part of the catchment where each meter would count.

[clarence]

This brings to mind the proposal to raise Tallowa Dam / Lake Yarrunga by (from memory) 7 metres, about 12 years ago (in which I was somewhat involved).

As with the Lake Yarrunga proposal, one of the big issues is how impacts will be managed under the Wilderness Act (which effectively prohibits all such human impacts). Overlaid on this would be World Heritage legislation, which was not a case in the Yarrunga proposal.

It is always a difficult issue when two Acts clash (eg mine rehabilitiation under Mining/Environmental Planning Assessment Act versus Heritage Act).

Having seen how these conflicts are resolved in past experience, it seems to be a very political (rather than legal) decision- and the decisions seem to be kept as far from scrutiny as possible. It is far from a clear cut and transparent process.

At the time (about 2004) any conflict between the Wilderness Act and other legislation was unchartered territory. This is probably still the case.

Clarence

[robl]

It seems that those in power have decided to increase downstream safety from that described in the following webpage.
I can't imagine what happens when the "fuse plugs" go but it must be better than dam failure.
I guess that they have decided that the "fuse plug" solution was just temporary and heavy downstream flooding is now unacceptable.

http://www.waternsw.com.au/supply/Greater-Sydney/safety/warragamba-dam-auxiliary-spillway

Associate Professor Khan offers a different solution for this problem. I am sure there is other stuff on the web.

http://www.smh.com.au/nsw/warragamba-dam-disaster-warning-downpour-now-could-devastate-western-sydney-20150827-gj8wif.html

Global warming is increasing the risk of extreme events occurring, according to most scientists, so we must be thoughtful.

[DarrenM]

I regularly see the damage in low lying areas around the Hawkesbury etc. Loss of property, roads cut off for days and I've personally lost work in the areas prone to flooding. We've spent tens of thousands of dollars pumping water out of property and cleaning up after big rain events. Three or four in the last 12 months alone.

I'm all for conservation but there's a lot of people affected downstream and a truck load of money during cleanups.

[gayet]

What about moving the people etc out of the flood prone areas? Do it once and the problem is solved. Can't be more expensive than raising dam walls and potentially stuffing up other river systems up stream of the wall.

Why does a bad decision years ago take precedence over a solution now? Yes the people being moved may not like it, but they generally don't like the impacts of a flood either. Sometimes, human feelings should not come first.

[kjbeath]

...they have just finished spillway work in the last few years to prevent wall failure for 1 in 700 year floods

Does this mean that each year there is a one-in-701 chance that the dam will fail? Are there any statisticians here who can interpret this?

I think it was actually 1 in 1000 year floods, but it means there is a 1 in a 1000 chance of the dam failing in a year. That probably is a conservative estimate. There just isn't a lot of data for making this sort of estimate.

[GPSGuided]

We are getting a lot of 1:100 to 1:1000 years events around the world these days.

[robl]

I did some more searching.

This appears to be the latest report. A "must" read.

http://www.infrastructure.nsw.gov.au/news/currentnews/hawkesbury-nepean-flood-risk-management-strategy.aspx

And it evolved from the one below.

http://www.water.nsw.gov.au/__data/assets/pdf_file/0005/548987/key_hawkesbury-nepean-valley-flood-management-review-stageone-report.pdf

That valley might be an interesting place to live!

[DarrenM]

What about moving the people etc out of the flood prone areas? Do it once and the problem is solved. Can't be more expensive than raising dam walls and potentially stuffing up other river systems up stream of the wall.

Why does a bad decision years ago take precedence over a solution now? Yes the people being moved may not like it, but they generally don't like the impacts of a flood either. Sometimes, human feelings should not come first.

I'm conflicted on this one because of the consequences to the Kowmung.

If you are familiar with the general low lying western suburbs along the entire Hawkesbury basin you will realise the cost would be astronomical and the logistics almost impossible. The amount of working farmland, businesses, thousands of homes and people having to move etc. There has already been millions upon millions of dollars spent bypassing flood prone roads around the Windsor area and I have heard there are plans to raise the Windsor bridge.

There are also many side creeks that back up and take days to subside etc. Once again, the Damn is about to spill over at what cost downstream.

I'm not sure what other options there are really, and to think we were on water restrictions and a desal plant was built not that long ago. I'm not an advocate of destroying any wilderness areas but how do we get around the problem? It's a tough one.

[GPSGuided]

I agree with Darren, it's a very difficult situation given the historical precedent of human settlement in the downstream area and subsequent urbanisation. Of course, there's always that voting factor, that human can vote but plants and native animals can't.

[ribuck]

From nature's point of view, floods are not a bad thing. The floodwaters wash away lots of fertile soil, and it's much better for it to be dropped on the floodplain than washed out to sea or deposited within the dam. Of course there's the problem of how to keep people safe, but one large flood-proof elevated structure every square km or so should do it. We are talking about a once-in-decades occurrence, so people within the flood plain can't reasonably expect not to be inconvenienced to some extent.

If we decide to trap the flood in the Warragamba Dam (where it will dump its sediment), then I like the idea of keeping the dam at 80% capacity for this purpose rather than raising it. Then, we can re-draw the "3km from stored water" prohibited area. This will expand our bushwalking options, and allow for eventual regrowth in the freed-up area.

[GPSGuided]

We are talking about a once-in-decades occurrence, so people within the flood plain can't reasonably expect not to be inconvenienced to some extent.

In this age of extreme entitlement, you know this argument won't fly, right?

[Grabeach]

Then, we can re-draw the "3km from stored water" prohibited area. This will expand our bushwalking options ..........

Wishful thinking on that one. You may not realise that the original intention apparently was to keep bushwalkers out of the whole Special Areas Restricted Entry region, not just the No Entry '3km' zone. No way will the No Entry Area contract. However, if the stored water is increased, then the No Entry Area will likely be increased as well.

[Giddy_up]

What about moving the people etc out of the flood prone areas? Do it once and the problem is solved.

And it's been done before, whole towns have been moved to facilitate the Snowy Hydro program etc.......


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[Giddy_up]

I wonder if any of the traditional land owners have been consulted about this and if any of their sites of significance would be lost!


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[Grabeach]

.... whole towns have been moved to facilitate the Snowy Hydro program ....

The Snowy Scheme relocated about 1,000 people living in small easily movable wooden houses to unlimited land nearby. Not quite the same as 134,000 living in larger (many brick on slab?) houses in Sydney.

[Giddy_up]

.... whole towns have been moved to facilitate the Snowy Hydro program ....

The Snowy Scheme relocated about 1,000 people living in small easily movable wooden houses to unlimited land nearby. Not quite the same as 134,000 living in larger (many brick on slab?) houses in Sydney.

So your saying it can't be done, is that right.


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[Grabeach]

So your saying it can't be done, is that right.

Not saying it can’t be done. Technically I’ve no doubt it could. Whether everybody would want to pay for it is another question. I’m just pointing out some of the differences between what was done then and what would need to be done now.

[DarrenM]

.... whole towns have been moved to facilitate the Snowy Hydro program ....

The Snowy Scheme relocated about 1,000 people living in small easily movable wooden houses to unlimited land nearby. Not quite the same as 134,000 living in larger (many brick on slab?) houses in Sydney.

So your saying it can't be done, is that right.

I think you would need to spend time traveling along the entire area affected to truly understand the size and scope of the problem. It's massive in so many ways.

I wonder if any of the traditional land owners have been consulted about this and if any of their sites of significance would be lost!

This will no doubt be lower down on the agenda unfortunately. The whole of Sydney was built without consultation.

[Giddy_up]

[quote].... whole towns have been moved to facilitate the Snowy Hydro program ....

The Snowy Scheme relocated about 1,000 people living in small easily movable wooden houses to unlimited land nearby. Not quite the same as 134,000 living in larger (many brick on slab?) houses in Sydney.

So your saying it can't be done, is that right.

I think you would need to spend time traveling along the entire area affected to truly understand the size and scope of the problem. It's massive in so many ways.

I wonder if any of the traditional land owners have been consulted about this and if any of their sites of significance would be lost!

This will no doubt be lower down on the agenda unfortunately. The whole of Sydney was built without consultation.[/quote]

I know the area well, it's just money and a want to do it that's needed and a shame about the indigenous input but you're quite right on any consultation with them.


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