You are here

TasWater – Water Restrictions

Dr Rosalie Woodruff MP

Dr Rosalie Woodruff MP  -  Wednesday, 1 December 2021

Tags: TasWater, Water Restrictions

Dr WOODRUFF - Thank you, Dr Gumley, for your introduction. I read the report from TasWater in the paper today about the water restrictions that will be in place in Hobart over summer. I was surprised. I think many Hobartians would be surprised, given the level of rainfall that we have had, to talk about water restrictions.

From the releases, I know there are obviously some background issues. I would like to tease those out. We have had the wettest October since 1947. There is no doubt that there has been a lot of rainfall. You have said that this is due to heavy rainfall causing sediment and debris to run into rivers, and also gestured to maintenance issues that need to be undertaken.

Can you please explain how long it normally takes for water to clear after heavy rainfall? My understanding is that it is within four hours, two days - at the most a week.

Mr BREWSTER - It varies. Bryn Estyn is the key in terms of run of river supply into the greater Hobart network. There is an ephemeral creek there, which runs when you get a certain intensity. When that happens, you get very high-turbidity water, and that can slow down that plant for quite a while. It is not just a matter of the number of days. When we're looking the Bryn Estyn, for example, and the water quality coming down the Derwent, we're looking at the whole summer and all of our demand profiles.

We have analysis done on what's the local demand through the summer and what's the likely supply issue? Hobart is largely a run of river systems, as you would probably know with Bryn Estyn. Bryn Estyn's 60 per cent of the water supply, so when that's down you have very small overnight supplies in the network. You've got to be thinking, I have to catch that up, what's going to happen tomorrow? Generally, we don't look at it in terms of three or four days, we look across the whole summer in a demand/supply match.

The primary challenges we face are: whenever we have turbid water coming down the Derwent and we have to slow the plant down, particularly if the creek, which is unfortunately named Mikes Creek, runs right next to the water treatment plant and feeds in that turbid water. With the intense rainfall, we have challenges at Risdon Brook. That water supply is very difficult to use at the moment. The more intense rainfall we have, the more sediment is washed into Risdon Brook. We have the Ridgeway Dam lowered. We also have quite a bit of wave action when it's lowered; you get wave action when you get the wind, it pulls in the sediment from the side of the dam. That then restricts our ability to use it. Similarly, we have been upgrading the lower reservoir as well, that's another source on the mountain, and that's also turbid. Because of all the intense rainfall we also have turbid water coming out of our other primary supply, the Fenton Line.

Most of our alternative supplies are challenged at this point. We have to make a judgment. If I sign off on them after receiving all the information, I'm sitting there looking at, right, do I sit there and wait and one day we don't have enough water, haven't warned and prepared the community for water conservation and, suddenly, I pull it on on 20 December. We're only going to stage 1 at this stage, which is minimum restrictions.

Dr WOODRUFF - Thank you very much for that. You've said a lot of things. In the media release the reasons you've given the community are just about recent heavy rainfall causing sediment and debris to run into rivers. Why I ask the question about how long it takes is because, typically, I understand it would take a number of hours to a couple of days, at the most, a week at the most, unless there is something else happening in the catchment. There haven't been extreme bushfires with silt and sediment.

I would like you to provide some information to us about what's happening in our catchments. It sounds to me like the other reason you've given is not only turbidity, it's taste and odour. That is a question about the capacity of Bryn Estyn, which hasn't yet been upgraded, to deal with the drying in the upper catchments and the increasing algal growth as summer comes.

I would like to understand the real reasons behind these restrictions. Can you talk about whether it is taste and odour? Can you tell me whether it takes more than a week? What's happening in the catchment?

Mr BREWSTER - With respect, I think I just told you the answer. There's nothing there that I am trying to hide. It's exactly as I said it.

Taste and odour is a factor but it is very low at this time, so I am not seeing high thresholds of algae in the water. That could change; that often changes. When that occurs, again, that then challenges the capacity of the plant further. That's another factor but we haven't come out and said it's due to taste and odour because, right now, it's not.

As I said, when we look at it, we can't just look at Bryn Estyn. We have to look at the whole Hobart network because it's all interconnected. It's an overnight system so, in effect, there's very little storage apart from those storages I talked about. It's basically produce it, and as you produce it you store it overnight. If you can't replenish your storages - and we've had that - you're going lower and lower in terms of your storage in the network and, eventually, if you can't manage that, you end up on a boil water alert.

Dr WOODRUFF - To be clear, it's not sediment and debris that you're looking ahead to, into the summer period because that clears very fast. It is fundamentally -

Mr BREWSTER - No, I'm not saying that. That's not true. I am absolutely not saying that. I am not reversing our position. My position was clear. Sediment is an issue in all of the other storages, plus it's an issue at Bryn Estyn and it comes and goes at Bryn Estyn.

Dr WOODRUFF - It clears very fast. Within a couple of days.

CHAIR - Dr Woodruff, please.

Mr BREWSTER - Sometimes it would take longer.

Dr WOODRUFF - Does it clear faster?

Mr BREWSTER - Sometimes.

Dr WOODRUFF - So, if it doesn't usually take more than a couple of days to clear, I don't understand why you have water restrictions for two months.

Mr BREWSTER - I just explained why. I went through all of the other storages I said to you, it is a complete network. It is not one system. The Bryn Estyn system provides 60 percent of the supply to Hobart.

I was very clear about the system network. There is an issue at Bryn Estyn, otherwise we would not be spending over $200 million to address it. With the Bryn Estyn system, what we are intending to do is bring it up to 160 megalitres a day so it can ride through these things.

Having said all of that, I would have thought any message around water conservation and minor restrictions is a good thing, anyhow. At the end of that, it all costs. Fundamentally all this money has to be spent and then customers have to pay. We are always trying to balance these things.

Dr WOODRUFF - Dr Gumley or Mr Brewster, why aren't Tas Irrigation customers being warned about restrictions now, when Hobart residents are being warned about restrictions over summer? I understand that Tasmanian Irrigation and TasWater said they meet with you weekly, so why hasn't that warning been given to irrigators as well as residents?

Mr BREWSTER - First of all, they're not being put on restrictions at the moment, as I said earlier. If we put Tasmanian Irrigation on restrictions, that's a matter for them to decide whether they put their customers on restrictions, so we're not going to communicate directly with their customers. We communicate directly with Tasmanian Irrigation and it's up to them to make that decision. We are committed, with Tasmanian Irrigation, on a best-endeavours basis to keep that water going to them, as I've said.

That's really what it's down to, and I have no doubt Andrew and the team at Tasmanian Irrigation would be informing their customers as to what the situation is with the water. They would be across it, because we share that information, as you say, on a weekly basis.

Dr WOODRUFF - As I understand, the 25-year agreement between TasWater and Tasmanian Irrigation says that drinking water supply comes first?

Mr BREWSTER - Correct.

Dr WOODRUFF - And that irrigators can be restricted?

Mr BREWSTER - Correct.

Dr WOODRUFF - Can you table the agreement, please?

Mr BREWSTER - Chair, as long as Tasmanian Irrigation are fine with it, we have nothing to hide. No problem. I'm happy to table it.

Dr WOODRUFF - Thank you. From what you said before, it does sound like there's a bunch of things that are happening, that are leading to the Hobart water restrictions - accepting that they're just stage 1 at the moment; they're cautionary.

The communication to the community is about turbidity. It doesn't mention the other issues, and Bryn Estyn isn't online yet. Given that the price has changed - it was $160 million initially for Bryn Estyn, and now it's a $200 million upgrade - can you please give an update on the work that has been done on that so far, and how much of that money has been spent? I think it's scheduled to be finished in 2023.

Mr BREWSTER - Tony, did you want to cover that? Just before you do, I want to go back to the turbidity, because you keep implying that it is about the turbidity at Bryn Estyn, and I keep saying turbidity is impacting all of those storages. It is a broader issue, yes.

When you're making a media release and putting the communications out, it's always a judgment about how much detail you want to put in there. I've agreed to do an interview tomorrow. I'll open all of that out and I'll take all the questions, but there's nothing hidden here. These are the facts. All of our systems are impacted by turbidity.

Mr WILLMOTT - The Bryn Estyn treatment plant is currently around 20 per cent constructed. We've poured about 3500 cubic metres of concrete into the site, of 11 000 in total, and 800 tonnes of steel has gone into the site so far. It's a significant construction site that's underway. Those major components will be completed by mid-next year, and as we continue to create those structures we'll start the mechanical and electrical installations.

Dr WOODRUFF - Okay. Did you say it's still on track to finish by 2023?

Mr WILLMOTT - Yes, it is on track.

Mr BREWSTER - And it's on budget.

Mr WILLMOTT - Can I add that the total project budget is $243.9 million.

Mr BREWSTER - Rosalie gave the original number. The way our estimating works, as with everything, is that you do a high-level estimate up-front, without your detailed analysis - and this is one of the reasons we have the CDO, so you don't go in with under-cooked numbers. That's your first-cut number that you put into your price and service plan, leading in, then you undertake the next level of estimation.

Then we do a design estimate, so we work through all of that and we get a base design. When we have that, we go to what we call a 'TOC design' or a 'TOC level', so that's when we go to the market. We get all of the pricing and we do not sign a project off until we have a high level of confidence that it is going to be delivered for that price, and that stage includes a complete independent estimate by independent estimators.

That goes to the board when we are in that level. We have a total out-turn cost. That is where we get to the 243. It was slightly above that when it came back. I sent it back, and said we need to do another value engineering exercise, which we did. We hired someone independent again to come in and re-evaluate all the estimates. It held the project up three or four months while we engaged someone else to make sure we had extracted every bit of value judgment. We pulled out a couple of things we felt were not needed.

That is how the process works. One of the benefits of doing it this way is that we are building it in a modular basis. At the end of the 30 to 40 years of this current cycle, we would be able to add another 40 megs to it, with all the base infrastructure. That is why we have gone down this path, because we are thinking the next 80 years, not the next 10 or 20 years.

Dr WOODRUFF - The Ridgeway Dam was something else you mentioned as part of the reason there will be restrictions this summer. There is reduced capacity at Ridgeway because GHD recommended that it be lowered by 4 metres for safety reasons. The briefing we had with TasWater some time ago about this indicated that there was an inspection underway. Can you please tell me if that inspection has been completed? If there were any reasons to make changes to that dam they would be very costly as well.

Mr BREWSTER - Correct. The trouble with the Ridgeway Dam is classic: you don't know the dam fill. You know how the dam is constructed, but you do not know the condition of the dam. So, this is a prevention cable dam, from recollection. You do not know what the condition is. Engineers are making assessments without fully knowing the condition of those cables that hold the dam up. GHD Pty Ltd did an assessment. I think Entura did another assessment. Our people did an assessment. They did not come together, so there are differing views, as often happens with engineers.

Because of the amount of money involved, this will, potentially, be a significant expenditure. We are not rushing in. We will just take the last report we got, because that could cost our customers tens of millions of dollars. What normally happens is - and this is standard practice - we then go to international dam consultant experts to review it all. We are going through that at the moment, and then we will make a final decision on what we do with Ridgeway, to ensure what we do is value for money, and we do get the long term life out of it.

Dr GUMLEY - We have to remember the dam is 104 years old already.

Dr WOODRUFF - Yes. How long for the investigation before that decision is made?

Mr BREWSTER - The investigation is complete. It is with our people. They are working their way through that at the moment. It is probably another two or three months before we will sign that off in terms of the final results. Then we will re evaluate the estimate to assess what that means in terms of the final cost to upgrade that dam.

In the meantime, we have put silt curtains in to try to stop the wash-off. They help a little. As you can imagine, the water level is down, the banks are exposed, you get a bit of wind, and you get rain, and that turbidity washes in, so we put some silt curtains in.

We are looking at doing further things, because even if we chose tomorrow to upgrade that dam, it is not going to be upgraded in two or three years. We need to have a medium term solution.