Environmental Flows

Australia has developed this procedure for water storage dams whereby a quota of dam water labelled "Environmental Flow" (EF) or "Environmental Release"  is periodically released to maintain wildlife values downstream - a concept that on the face of it sounds all well and good.
The exact specifications of  the releases can vary seasonally,  from dam to dam and  I expect the various  States have their own guidelines too.
Andrew Bolt has an interesting blog article drawing attention to the Victorian Govt plan to release 10GL of water into the Yarra River at a time when the river has reached minor flood levels due to above average rain in June. All this at a time when Melbourne dams  are only 36% full  with consumers  on water restrictions - not to mention high priced water which will only increase in price further as seawater desalination comes onstream.
Melbourne Water has a webpage tabulating Thomson Dam EF for most of the past decade - I was very surprised to note that for the years 2002 - 2008 - EF averaged 35% of inflows or almost 4 times minimum EF beneath the dam.  No wonder the dam levels can not recover  -  the Govt is constantly pulling the plug.
I have a blog article myself titled - Are we being conned with excessive water charges ?      which goes into the way Australian water policies have changed over a decade in the direction of more expensive water.
Living in Canberra I have tried to get a handle on  EF as applied to the Canberra water supply - this is not easy - the water and electricity utility ACTEW publishes  at intervals a   "Water and wastewater performance report" (look down the left side) which gives a monthly graphic for each dam covering maybe a year - and the EF usually exceeds the target  amount.  A few ACTEW Annual reports - 2004, 2005 and 2006 have a graphic showing EF for a few years.  I can find no data in Annual Reports post 2006.
Then in the 2007 report there is a graphic showing several years of dam inflows.    Oddly for an engineering and science organisation that no units are specified for the graphic - but we assume they are thousands of Mega Litres ML or Giga Litres GL.  So the six year average is just over 50,000 ML or 50 GL per year.  ACTEW do not make it easy by sometimes quoting data on a finacial year basis and at other times on a calendar year but lets compare the six year of EF from  2000/2001 to  2005/2006 with the above 50 GL per year average inflow 2001-2006.   The answer is 45 GL per year average EF.   So for the period of years typified by below average rainfall the Govt is tipping 90% of inflows out as  Environmental Release - no wonder our dam levels have been dropping.  Now the average EF figure is influenced  by the 2000/2001 number being 88 GL so lets take that out - the 5 year average EF is then 36.5 GL. Still a whopping  73% of average  inflows.
I wonder if the entire policy surrounding EF would stand up to proper scrutiny.
We must remember that all our dam infrastructure has to be so much larger and higher impact - capital and operating costs  etc have to be so much higher than they need be to cope with these extravagant environmantal water releases.

27 July 2010