Wednesday, September 19, 2012

QC7 - Is water quality likely to be the biggest natural challenge if a causeway is contructed?

Probably. (Noise at certain times ? See much earlier posts for visual impact )

Well published water pond planner Nick Romanowksi is, like many,completely opposed to the idea of changing the lake in any way at all ( Colac Herald 31st August)
As an ecologist I have a lot of sympathy with his view that managing water quality will be a difficult issue.I don't however think we should not modify the presently highly modified systems  just because its seen to be interfering in nature . The water quality is very poor NOW because plants and animal can't reliably use its huge nutrient load.  Decomposers are the main functioning biological elements  operating in the lake at any one time.
What we do need , in my opinion,  is to make sure we are working with nature , not against it ; That we are working with natural systems,  not presuming they will not change and that we cannot  be part of that change to more diversity too .As stated previously the water body does not function as a stable ecosystem because its very shallow ,wave prone with its dispersive clay content not allowing consistent algal growth .
I can't see any real reason why we can't have a  more " natural " lake up north than we have ever had and a more diverse stable water body to the south by planning development and design systems  that are thoroughly committed to managing nutrient loads  and using the earthworks for a road to do much more diverse things to the water bodies adjacent . There will be no other time we could afford to consider anything else. 

Time for your questions? 

Tuesday, September 18, 2012

QC6 How deep is the soft mud and quicksand ?

The map shows the  approximate key sources for sand and sealing type basaltic clays
Preliminary surveys surveys done in 2008 by the government suggest a slightly consolidated average depth of mud of around 800mm .The high organic content of this material  can be expected to limit its usefulness near causeway foundations .  It may be that soft materials extend deeper but such softness can be dealt with, in many cases by the use of engineering fabrics and water proofing.  The actual viable foundation depth is a question is best left to Vicroads to continue to clarify.
There are old sandy beach ridges underneath the basalt type clays laid down in recent centuries, but they are assumed to be small in overall extent ( eastern banks and near creeks  for eg )  .
The sound water holding capabilities of surface clays is a positive sign for both designing  to preventing sands from becoming unstable and to prevent surface water leaking away easily .
None of the above speculation is sufficient to make clear the difficult task of finding foundations. Readers will note  that the recent design options for a causeway ( 41 million ) do not suggest high cost of foundations is an issue.  

Q5 How fair is it to say its not a natural lake ?

 In my letter to the paper last week,  I should have perhaps put "natural"  in inverted brackets .   As a scientist I find it difficult to know what the commonly used word" natural"  means ( it has philosophical implications too ) because natural processes ( a clearer term)are always adjusting and accommodating to change. I don't accept the common perception that natural means unchanging and final - nature is more about processes and life cycles  than it is  about a static state . Its not sound , for example,  to try and preserve things in a museum as some evidently want to. Natural processes  preserve and protect by seeds and spores and eggs and by adjusting to pressures of change.  Perhaps the most accurate way to describe what we have before us right now  is "not entirely natural" because of the higher water level maintained over the last 30 years at least.

Lunette ( shown in blue) type lake systems are by nature shallow and ephemeral,  and our artificial raising of the water since settlement has meant, that its more like a lake than it would otherwise be.( thankfully no one drained it like they have others )
Some people imagine we can go back in time " to nature",  but I don't think  its that simple or desirable to try and do that . Nature is always changing and life cycles are short in "our lake systems - incl streams and sub surface flows ".  I think its better to ensure that we work with nature not against it ; Better  to move forward than assume we can go back to a time when things were" better".
As throughout its history,  the lake forming processes have been a changing and interchanging thing( climate , season , drought, grazing , daming,clearing)
The low lying area around Lake Colac formed when lava flows occurred to the north, west and east and blocked off (filled in old creek channels) the natural drainage to the Barwon River system .
The area became a lake , like so many in this area to the north , in  a very dry period several thousand years ago. The clay floor was exposed during the long summer and blew into the clay lunettes ( shown as blue )

Q4 What would happen if we could raise the water level of the whole lake ?

Basically just erode the banks back into the lake esp the eastern ones. Self full filling action .

Notice how wide the beach barrier is now on the eastern shore .  This erosion of wind blown eastern banks is  infact what happened in the twenty or so years prior to it drying right out .

Q3 What functioning water ecosystems are there?

Only very unstable ones . One's that eels can cope with.

Because of its very shallow depth, high wave action and dispersive clay floor , our magnificent expanse of water seldom operates as an ecosystem. The murky muddy water that kills off recreational interest in our lake, is the very same dark force that keeps it largely unproductive as an ecosystem. In those brief periods when the water is calm and the fine dark clay tends to settle, algae proliferate rapidly because the nutrient store in the water  is very rich . But there is no reliable light source to keep the systems going.  The water is too shallow to easily prevent its choppy habits and the temperature goes up and down too much to encourage fish. When the wind picks up, the clay below is resuspended through the water column; the algae die and so do the animals that live nearby. It is these unique lunette type ponds that create the unique risk of blue green algae death ; its building up on the shore;  and the killing stock who eat it.   

Thursday, September 13, 2012

QC2 The Bad news First

A causeway across Lake Colac is needed to save it from dying.   A causeway bank provides a way to provide the deep water that has never been reliably there before.  It’s time to do something about Lake Colac, and for the first time in our history, we can.  
This sort of feature will still occur when the northern part of the lake dries out 

Sure we can keep raising the exit levels at Meredith  Park,  but the swamp effect will increase as vegetation takes over from around the edges , as less and less runoff comes in ; The shallow water and rich nutrients drive  rooted plants to thrive ( picture of grassy beach near the boat ramp ) Deep water, by its very nature,  becomes less fertile   . As many have said, there will be some visual and audible impacts from a causeway bypass and there is a need to ensure new water bodies do not generate algal blooms too easily.  The actual location and development of any causeway basin works will require a lot more planning to make sure the outcome is the best possible one for all concerned. New beaches, pipes, deep water holes  must be designed to work well without much maintenance ;--the nature of sustainable systems. Everyone of us has questions so ask them here.

Q1 Why will current Lake Colac never fill reliably again?

About 700mm of water comes in from the sky and 1400mmm goes out in evaporation. That means there is an average  shortfall each year of 700mm.  To get this water requirement from the catchment land ( 7 times the lakes area), would take 100mm off each hectare of land in the catchment     That is still a huge amount of water.  ( about 10 times water stored in the West Barwon or 100 times the water stored in Colac storages) However we  could reasonably expect , to get 50mm average each year in run off,   so some doubling of effect would change things.  It is not unreasonable to get an average of 50mm of runoff off the catchment, but it’s impossible to get 100mm. The 2 creeks flowing into an about 1/3 reduced size southern section could be expected to fill that area every other year because the catchment to evaporation ratio would be more than doubled.
. There has never been enough water available to raise and retain the water level above the evaporation deficit, so about 18 out of every 20 years , the lake level is lower than we would want it to be - around swamp depth .  There has never been enough water coming in each year to keep it above 1600mm, even when the catchment had more runoff with fewer dams and much closer grazed pasture.
Something drastic has to happen to increase the runoff ratio and the only way is to reduce the southern lake size.

Tuesday, September 11, 2012

Autumn 2012

Sunset August 2012

The lake might not be filling up much but we are getting our normal rains

Feb 2012

Great to see Pelicans back for a while during February . They used to be so much a feature , even though their main food source was the tip.-Innovative recycling has been a tradition around here for decades .
The current group travels in packs , but when feeding , often seen in a circle,  diving together - a beautiful circular synchronized swimming dive " put your twin beaks in and your twin beaks out, keep your wings together and shake the back bit about" . Lots of food and birds near the edge at Yacht club ramp , but habitat diminishing as vegetation is eaten off.The water looks clear from here but even though the water is only 200mm deep you can't see the bottom.An eel or fish lives happily disguised in 150mm of muddy water directly under the Yacht pier ( where Cranes can't get him?)