Viewing 8 posts - 1 through 8 (of 8 total)
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  • #859488

    PT48
    Participant

    For the past five weeks I have not been able to fish the streams of the Derwent catchment due to terrible weather and dangerously high flows. This is the first November and early December that I have not caught a fish in Tasmania. Very frustrating. And yet, Greater Hobart is soon to go onto water restrictions. I find this situation inexplicable and am wondering if there is a bright spark out there who can explain this state of affairs to me (and I mean the water restrictions and not the weather).

    With thanks.

    Peter

    #859519

    flylife
    Moderator

    South east irrigation demands with very dry conditions in the southeast?

    #859520

    PT48
    Participant

    So that explosion in vegetable gardens between Sorell and Forcett is to blame? But there is currently a huge amount of water at the head of the Derwent system, most notably in lakes such as St Clair and King William and rivers like the Tyenna are running at nearly six times safe fishable height (which experience has told me is 300 million litres per day). I just find it incredibly hard to believe.

    #859521

    flylife
    Moderator

    Must be using more than they can pump out of the Derwent. Demand for veggies, vines and orchards is over the top this season and irrigation allocations always run out in a drought year. ☹️ Craigbourne has been dropping fast too. Environmental flows are just wishful thinking in the new world order.

    #859531

    BarryJ
    Participant

    Yep, the pumping line from Bryn Estin(sp?) to Hobart is hopelessly undersized and even though plenty of water is flowing past & out to sea, Hobart reservoirs can’t be topped up!

    #859532

    PT48
    Participant

    Thank you Barry – now I understand. This will be a challenge for Minister Barnett. Perhaps they could encourage tourists to not take 30 minute showers!!

    #859572

    DrGraham
    Participant

    The situation with Hobart’s water is not as simple as it seems. Hobart, and east coast Tasmania generally, has come out of a dry winter and spring has been no better. Hobart had poor rainful in June and July, above average rainfall in August, but significantly less in the following months since; September 66%, October 29% and November 75% of long term average. Bear in mind that Hobart is Australia’s second driest capital city. October was also exceptionally warmer than the norm. Consequently, there has been a higher demand for water in all sectors, e.g. domestic, commercial, agriculture/irrigators etc, but they are not solely to blame. The bigger issue is the ability to supply water to Hobart, and the population is growing, albeit slowly. Hobart gets its water from three sources. Bryn Estyn normally supplies 60% of the water (85% in summer) from the Derwent River, Lake Fenton in Mount Field National Park supplies 20% (mainly in winter) and is rain fed, and Ridgeway Dam which is also rain fed through water collection off Mount Wellington. Risdon Brook Dam is backup storage from Bryn Estyn. Risdon Brook has only come back on line. Ridgeway is 100 years old and in need of repair and upgrade. Engineers are keeping that dam 4 metre below capacity for safety reasons. That is a substantial amount of water that cannot be held. Bryn Estyn is 56 years old and is also in serious need of upgrade at about $160M and that is about 3 to 4 years away. So we end up with the “perfect storm” situation of much lower rainfall than normal over winter and spring, a growing demand for water, and an infrastructure that cannot deliver even if water is plentiful in the Derwent system. As for the Tyenna, the water flow does change rapidly in response to systems passing through. For ten days prior to December 3, water flow was about 200-400 ML/day. It then shot up rapidly to today’s flow of 3144 ML/day thanks to the Low pressure system that parked itself south of Tasmania for the last 7 days, providing the miserable weather for the past week. The Low is finally moving but the water flow is still going up which suggests it’s mainly snow fed. It may take a while to clear. A pity, as it is normally about now that I start thinking about fishing the Tyenna.

    #859689

    PT48
    Participant

    Thank you Dr Graham, that is really useful information. Clearly, somebody has been asleep at the wheel in terms of seeing the problem coming. The big question is what are the authorities going to do to remedy the situation and which user groups are going to suffer in the interim?

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