Why all the wastewater from Black Rock ( Geelong ) would be of no help to keeping the lake up

Even if we could afford the pumping and piping costs, the extra water would only last a few hours at this time of year . While the lake remains a permanently large open water body,  its evaporation volumes will be huge . Drying out  is part of its life cycle 

The 50 or so megalitres  a day ( The daily volume out of  Geelong area) would only add a few centimetres a month  and cost a fortune to get here . 

Pipes alone would have to be at least 750 mm diameter( some would argue less, but the friction would be higher  ) with multistage pumping and very high risks of failure because of the huge energy and heads involved .
Even at 20 cents per KW,  the pumping cost alone would be over a million dollars a year.
 
Total yearly evaporation from the lakes surface is at least 1300mm  We don't notice the lake dropping because our 700 plus  rainfall comes over a wide part of the year (like this year ) and we do get some runoff . The runoff is not nearly as much as we used to get-- see previous posts where the permanently changed character of the catchment runoff capability is described.

To raise a  cubic metre of water( one tonne ) up one metre takes,in theory  a  kilowatt of power .In practice any pump will use more than that to do it   
 
Lake Colac is 115 metres above sea level. 
We have a wonderful  but very large lake,  but it remains an unpredictable unreliable and changing deathtrap while we try to maintain its height across all sectors,  all of the time. Its water is so rich that it will grow  anything  in it,  in the brief  moments when the wind stops.

Vote at your local corner store to get Vicroads to , at the very least, investigate properly the cost of earthworks that would work to save and improve the Lake  .  Maybe you have questions. List them below 

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Why Lake Colac won't ever fill again reliably unless we do something something drastic

 This item was posted originally in September 2012

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) . Most of the runoff comes in through the two creeks to the south . 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 size of the lake elements..

Stop blaming the discharge agents - Eutrophication of Lake Colac happens readily without any extra nutrients

Past Pollutants aren't the reason our lake is Eutrophic . Lake Colac is one of the most fertile lakes in Australia. Its unstable and highly nutritious nature is natural 
 Avoiding the high risk of lake death from eutrophication is hard enough without being distracted by ongoing criticism of pollutants. Colac herald 17th January 2021 .
 
Shallow water  will find and use enough Nitrogen and Phosphorus( the key factors )  to grow the algae WITHOUT bringing and blaming water and drainage authorities . 
The CCMA could put in another 100 pollutant traps and it would make no substantial difference to the water quality in Lake Colic . 

To be more useful and practical , it would really help the progress of the discussion if the agencies like CCMA DWELP  and the Shire accepted the big picture of a dying lake needing help. 
 That way , instead of dreaming up impossible, ineffective half baked solutions ( like dumping sand ) that  suit noone including the  natural  processes, Colac and district can greatly improve its surroundings for the future. .