This news item caught my eye – Dangerous behaviour as people canoe on the Harvey Dam which could overflow any moment –
Seems counter what we would expect in view of the decade long propaganda from WA water authorities about low dam levels – “our drying climate” slogans – rain never filling our dams – Perth will die etc etc etc.
I see these dams are part of Harvey Water
Map Harvey Water dams –
Levels Harvey Water dams –
Harvey Dam at 56GL and Wellington at 180GL are the two largest and are both full. Is there a reason in rainfall ? or catchment factors why these dams are full now ? At the exact time Perth water supply catchment dams are struggling to average 40% full.
Harvey water is a privately owned irrigator cooperative. Which will make them pretty much immune to greenie pressure to not manage catchments for maximum runoff, unlike the Water Corporation. Although their website says the Water Corporation manages their dams for them.
One other factor that occurs to me is that their water demand can be managed – reduced allocations to irrigators. Which would indicate the full dams result from failure to forecast this wet winter. Although the dams have filled every few years in the past. Most recently in 2007.
Still you ask a valid question. Why are these dams full, while not too distant Water Corporation dams are far from full?
Harvey Dam catchment is 126sq km whereas the Wellington Dam catchment is a huge 2823 sq km (compared to 3500 for all Perth water supply dams). Obviously the Collie catchment that drains into Wellington dam is not all forested. Would be interesting to compare catchment rainfall to dam inflows over a couple of decades for Perth dams vs Wellington.
The Collie catchment has salinity issues and Wellington dam water is weakly saline – to improve dam salinity circa 20GL or more PA of higher salinity water from low in the dam is released from the dam foot and runs to the sea.
Do Perth readers recall from 5 to 10 years ago Agritech Smartwater and their proposed Wellington Dam Water Recovery Project to build a desalination plant to treat this waste water from Wellington dam and supply it to Perth as drinking water at the predicted cost of the then future Kwinana desal plant ? WaterCorporation successfully convinced Govt over the years to not allow this sensible project to see the light of day.
I see this marvellous page from WA Hansard 17 May 2007 where Premier Carpenter says – ” It has stopped raining in the south west of Western Australia. The rain no longer falls from the sky in sufficient quantities to fill the dams to fill the pipes to fill the cups for people to drink.”
A skim through this page gives a flavour of how years of WA Govt water authorities “pro-seawater salination – anti-rain” propaganda had coloured the responses of a normally sensible Premier. To mention the word “dam” raises the level of tension in the chamber somewhat. Not a subject that Labor could debate sensibly.
The Collie catchment is mostly wheatbelt. Less than 10% forested and that %age will not have changed much for decades. Don’t have any figures for wheatbelt runoff, but I’d expect it to be highly variable year to year.
There is no doubt that the catchments for the dams near Perth have not been maintained since the 1970s. This is despite Water Authority field staff wanting to maintain the catchments to a standard to allow effective run off. Factors that contributed to this “imposed” neglect were:
a) political, a desire to appease “greeny” supporters, b)The increased influence of C.A.L.M who although sharing the vesting of the catchment reserves over ruled decisions made by the Water Authority c)Pressure by the residents of the metro area to stop controlled burning because of the prevailing wind causing a smoke problem in the city.
It is conjecture, but it is possible that the Caddoux earthquake at that time damaged the dam structures and that the publicity given to Al Gore presented a ‘Convenient Untruth’ for the Water Authority Engineers who were monitoring the dams’ movement, to be able to take the oportunity to reduce the “load” on the dam wall without drawing attention to the wall’s deteriorated condition and cause concern to the residents down stream from the dams. After all Mundaring Weir is over one hundred years old and does have significant cracking.