Hinze Dam Stage 3

Just the other day I was listening to ABC radio and heard some GCCC representative (didn't catch the person's name) making a point about how the Stage 3 of the Hinze Dam had now doubled the water supply for the Gold Coast.

Well you know, its sort of got some basis in fact but at the end of the day its what the most optimistic would call "spin doctoring". Another way of looking at it is that its just not true.

In fact the Stage 3 of Hinze dam has only added something like 12% to the water supply of the Gold Coast.

So lets have a quick look at the facts. From the SEQWater site dedicated to the project one can find out fairly quickly some basic facts:

• Completed in 1976, Stage 1 of the Hinze Dam provided a storage capacity of 42,400 million litres,
• Stage 2 in 1989 increased this to 161,070 million liters.
• The Stage 3 project will raise the Hinze Dam embankment wall from 93.5 meters to 108.5 metres, providing a total storage capacity of 309,700 million liters.

So from basic maths one would simplistically think that 309.7 divided by 161 is pretty nearly double (without splitting too many GCCC hairs) The devil of course is in the details.

background facts:

Stepping back for a moment consider that a dam is just a blockage in a river to prevent the water that flows down the river from escaping. The intention is to trap that water for ourselves, to give us a water supply. Clearly then its the stream flow of the river which is most significant here rather than just how high the wall is on the dam. It may seem obvious but building a dam on a river which has no flow will not magically produce a wonderful water supply.

Because reality is not simple. there are other ways water gets out of the dam than by the pipes we put in to slurp out the water trapped by the dam. These include:

• evaporation losses from the surface
• seepage of water out from the soil into the area
• legislated environmental flows to keep some of that river flowing (noone wants to see the Nerang river turn into a dry river bed for example).

From my research (in my Masters of Environmental Science) I found that a "rule of thumb", in Northern Australia is that: the maximum utilization of average flows that may reasonably expect from a dam is around 50% to 75%. So having a bigger container to hold the water is not the significant issue, its how much water flows that counts.


So its not only about how big the dam is, but how much water it can yield. From the points above its clear that how much we can get out depends on how much goes and minus how much we loose while its sitting around. Seems obvious when you think of it that way.

With respect to evaporation one of the major factors is surface area. So if you fill the dam more, then as the water goes up its sides the area of the surface of the dam increases; which means evaporation increases.

The diagram here shows the sort of change in the width of the water surface as water fills a channel which gets wider as it goes up (like rivers tend to do).

As it happens back some years ago some engineers were engaged to determine what sort of yield we can expect.

During the drought crisis of 2003 it was demonstrated quite reasonably that we can rely on the Hinze dam (then at Stage 2) to cope with a yield of about 161 Million liters of water per day (but it was going down quite fast without rain to keep topping it up).

During that drought we started with the Hinze Dam (then at Stage 2) at 100% capacity, but the water usage of the Gold Coast brought the dam levels down to a smidge below 30% with just one missed wet season. Red warning lights were going off on the GCCC dashboard and emergency meetings were called.

Now if we had had Stage 3 in place back at that point the only thing that would have changed is possibly just how much water was in the dam, the rate at which the dam emptied would not have changed.

Its possible that the rains of January 2001 would have topped up the storage to greater than what the Stage 2 held, but looking at that graph, not much. Either way, you can see that as soon as those wet season rains stopped the levels of the dam started to drop, and fast too.

So since the amount of water available is a factor of the river flow, not the height one would not expect that the yield of Hinze Dam could provide much more water with simply increasing storage capacity.

In fact the Engineering analysis of the Hinze dam showed that the yield of the dam in Stage 3 rose from (an estimated) 191Million liters / day to 215 Million liters / day or an increase of 24Ml per day or an increase by about 12% Nothing like double is it.

I am certain that this information should now be well known within the GCCC.

For instance , this is the table of data presented to the Waterfutures Advisory Committee by the GCCC, when they were considering the water supply options for the Gold Coast. There is some variation (depending on who did the study) as well as effects on available water depending on assumptions of the effectiveness of water restrictions.

Summary:

Ultimately I think that its important that representatives of the Council present the facts to us about the planning, about the state of our water supply and about what the real results of changes are. Putting "spin" (nice word for bullshit) on things as critical to the community as water supply should not be entertained. Misleading the community is not something we should tolerate in our Local Government. If (alternatively) the speaker had not the faintest clue about what they were talking about then perhaps they should not be in that position either.

The population of the Gold Coast is growing fast, and in the time since the 2002 drought crisis the population has grown from 425,000 to over 591,000. Thats an increase of over 28%

Since that time we've also gained the Logan Pipeline and the Desalination plant, lets hope its enough for the next drought

water: planning for sustainability

The attention of the general public (as a group, not individuals) is generally focused on the present, but that should not be true of governance. One of the reasons for planning is to attempt to forecast issues and design around them, this is among other things the role of the town planners.

Water (as we all know) comes from the tap, and as long as it flows everyone ignores it. However it was (or so it seems to me) just a short while ago we were in the grip of a serious drought and water restrictions.

At that time (if you weren't yet living here) we experienced a drought where the normally regular summer high rainfalls failed to arrive. This resulted in a very worrying drop in the Hinze Dam levels to around 30% capacity:

As you can see from the data in the above chart the November 2001 through to Feb 2002 rains failed to arrive. Strangely this was regarded as the 2002 2003 drought (even though 2003 rainfalls were more or less normal). However people were (quite rightly) concerned about this as it was the first time that such a situation had occurred. Importantly though, it wasn't the first time such a weather pattern occurred.

Had we then had low rainfall for the 2007 year (I wrote my masters thesis on this in 2005~6) we would have been in a similar situation or perhaps worse. Looking at the last hundred and something years of data, we see rainfall in Southport and Springbrook (where the Hinze Dam catchment area is) like this:

Quite seasonal, and quite a significant amount of rain between Jan and April, but not much between June and Sept. The vertical bars on that graph represent the ranges of rainfalls, and the blue and green lines the average. You can see that 0 mm of rain in Jan Feb and Nov are not unheard of, so nix out climate change having an influence here ... Fundamentally this is about population growth, exceeding the carrying capacity of the existing paradigm and a lack of planning.

People started worrying and the Gold Coast City Council (amid a backdrop of hysterical media) succumbed to pressures and signed up to a pipeline to Logan to get some 35 Mega-liters of water per day from Logan to supplement the 180 Mega-liters per day being drawn from the Hinze (and to a lesser extent Little Nerang) Dam.

The GCCC responce also included an examination of alternatives which included the Coomera Pimpama Water futures plan. The Council was thinking in terms of Business As Usual (BAU) and obtaining more water (we always have to have more don't we) and began looking at alternatives like:

• getting more water from Wivenhoe (as if they have too much for Brisane's expanding thirst)
• pulling in more from a 'water pipeline'
• desalination (ask someone who lives in Tugun about that)
  

The council produced a number of documents suggesting that water demand would go up like this:



And offering suggestions on how to cope with this such as:

I however took a different point of view and thought that (basing my views on "Ecological Modernisation" concepts) that we could achieve more with less by moving into the modernisation process rather than just doing "Business as Usual"

As the population of the GC community is expanding, I undertook an examination of the water needs of the community via both the BAU method and looking at what could be done with a two pronged approach. 1) the inclusion of water efficiency in the home and 2) the suppliment of community water with rainwater tanks. Note that water efficiency is not just the simplistic (and unpalatable) "demand management" strategy where you use showers which produce an annoying mist or give people egg timers to suggest they have shorter showers.

I factored in a very modest 1% per annum reduction in community water requirement and I also added another "what if" situation of the rain water tanks. Factoring this in I came up with the following projection of water demand.




So, following the GCCC model of Business as Usual the water needs of the community grew exactly with the community population (as they projected) to nearly 480 Mega-liters a day, while the use of modernization principles to reduce water demands brought a growth to 250 Mega-liters per day but with a much slower peak. Adding in the water tanks with modernisation brought the overall use to a point lower than 2001 usage figures even with a population increase from 450,000 to over 1,100,000.

So there really is potential for the community here to cope with population growth via planning and modernisation.