Technical presentations

Video transcript

Chris Russell: Thank you for giving us the opportunity to talk about some technical issues in the drainage space, so we’ve called this ‘The Design Storm: Drainage challenges and design in TMR’. What we'll do is just present some typical flooding and drainage issues faced by TMR, we quickly cover our current approach, how the discipline is changing and how we're responding to this. We acknowledge our values and diversity policies and we are working with our teams to get those entrenched and that's something that we constantly work on.

So a quick outline, so we want to talk about the unpredictability of the storm events, that is, I beg your pardon, real storm events versus design storm events, current drainage guidelines, which Mike will talk about, climate change impacts and what that means for TMR drainage. Hydrology changes, there's big changes going on the discipline at the moment that we’ll talk about, urban drainage design, creeks and streams, a little bit on intersection safety and how that's changing and a bit of a wrap.

So let's talk about storm unpredictability. On the fifth anniversary of the 2011 floods it's timely to think about the importance of flooding and drainage issues. Traditionally we use a design storm to model drainage. What a design storm is, it’s an average storm, whatever that is, and the problem with storms is that they're not average – as the 2011 Toowoomba and Grantham floods showed us, and I’ll show you something in a minute on Grantham. These images are from Toowoomba and we remember the devastating impacts that they had – so let's have a look at Grantham.

This next slide shows you, what I’ve done here is taking the Helidon Stream gauge which is just upstream of Grantham and I've plotted on there the historical floods in Grantham from the time that that was operating, so it started operating in the late sixties, early seventies and so I put all the design events, sorry all the actual flood events on this chart and that's time along the bottom there and creek recorded water level going up the top. And what you can see there, I think you'll agree, there's a reasonable consistency, there and that includes the ‘74 floods which is a top dashed one, which was the biggest flood up until January 2011. And you're probably looking at that thinking, rate of rise – so how fast the stream comes up is fairly consistent there, yes? And so you probably think that as far as the people of Grantham goes, this was their understanding of flooding prior to 2011.

Ready for me to add the 2011 flood? Yeah wow, look at that. So two things really stand out of that, first of all have a peak was just so much higher than anything they've ever experienced, but the right of rise, look at that. If you look at that other floods they typically no more than about one or two meters per hour – 2011 that was over ten meters per hour that came up and of course as far as evacuation and that goes, you can't do anything in that other than basically as the people did climb on your rooms and hope for the best. So, but this is a real storm event, the variability in real storms is just staggering and and look at that that's a great example of what variability looks like. Also just to remind you that extreme events do happen. I was with a lawyer recently who said ‘Is a one in a hundred event really foreseeable?’ and I said to her ‘Yes’ I said ‘A one in 2,000 of entries that we foreseeable,’ so extreme events do happen and think back to the first of May 2015, that event was about 1,000 years and at the Moreton Bay Rail project and even more extreme heading towards Caboolture, so extreme events aren’t mythical things, they do happen and they happen all the time it's just that they don't happen anywhere regularly is the reality.

So storm unpredictability is a big thing, OK, Mike.

Mike Whitehead: Good morning, this graphic shows the documents, the guidelines, the standards TMR uses and the interrelationship with other guides used in the industry. On the left there is the Road Drainage Manual, that’s TMR’s document, it represents the department's policy for drainage. It's actually our primary technical reference for all people engaged in the non-specialised aspects of road drainage. So typical of what our regions do deal with on our road network and covers probably ninety percent of the drainage the department does. In recent times Austroads has expanded to give us a national approach and the Guide to Road Design has three parts, 5, 5a and 5b and those cover road drainage. TMR played an active role in the development of that and then in fact most of our previous version of the drainage manual has been incorporated, now as the national standard because of the work we did in it so it's quite successful. So we've now harmonised with that with the latest version of the drainage manual and those two documents work together. The other key document on the right-hand side here is Australian Rainfall and Runoff by Engineers Australia. That is the industry standard accepted right across Australia for hydrology. That document unfortunately the one that we're using, which is the current standard’ is dated 1987, so it’s around 30 years old and is desperately due for an update which we've been waiting for for now three or four, five years. So it is pending and it will have some significant changes to the way TMR is going to operate and and look at the hydrology and extreme events and Chris is going to elaborate a little bit further. There is a fourth document down here, which the Department of Energy and Water Supply look after, are the custodians of, that’s QUDM which is Queensland Urban Drainage Manual. It is predominantly around the urban drainage. For many years now TMR, and this document, have had a little bit of an informal relationship. TMR is focussed largely on the rural drainage which most of their network covers, while QUDM focuses more on urban drainage and the two documents share – one refers to the other. QUDM predominantly used by regional councils in the urban environment and developers.

Alright, the next one. Now a question comes up quite often with ‘Why is road driving so important? Why do we keep talking about it?’ Well road drainage is one of the most important considerations to planning design of all roads to ensure appropriate training is provided. Drainage is one of the biggest killers of our road. It can accelerate the depreciation of the asset if we don't get it right through poor pavement drainage – put a loaded vehicle on it, the pavement’s life is greatly reduced. It causes damage because the concentrated flows over our infrastructure, such as floodways, culverts and at bridge sites, and that is evidenced over the last number of years for the big recent events and we've spent a lot of money and repairing those sites. Adequate and economic drainage is therefore absolutely essential. Yes, as a department as an engineering organisation we could build infrastructure that could withstand almost anything, unfortunately it will cost too much to do that and is unrealistic. So achieving the balance of what is economical, what is the best the outcome, is something department has to continually grapple with and things unfortunately think change with public perception, community expectations and obviously the priorities of the government of the day. We need to look at accessibility issues and expectations of community and a good example is when the Ipswich Motorway was opened up – the community saw that there was an inconvenience to them for many years while that infrastructure was being built and they thought it was going to solve all their problems. Not long after opening, we had a very significant flood and the motorway was cut and the have community said ‘Why did we spend so much time and inconvenience building that piece of instruction the first bit of rain we get it’s cut?’ Again, it is an understanding issue with the community. Certainly for the protection of the investment that we make in the road infrastructure, again poor drainage can accelerate depreciation of that or force early replacement of that infrastructure. Safety of all road users is also critical. Almost every single rain event of significance that we have around the state is tagged with someone being washed off a road way and losing their life. Even people in the street down here can be knocked over by flows and curves and again hospitalisation, while it's not a death, it's still inconvenience and people suffer. And the last one is the protection of the environment. Again the water is a transport mechanism and our roads carry a lot of heavy metals, rubber particles and oils etcetera and even dangerous goods on the back of them. The road is a concentration of that, water hits it runs off into the environment and can cause considerable environmental damage so again, it's another challenge for the department. Back to Chris.

Chris Russell: Thanks Mike. So we'll just talk a little bit of that climate change and then hydrology methods which are changing both changing. Firstly climate change. Now sadly there is no good news in climate change as far as drainage goes – the two major impacts on TMR drainage are firstly increase in mean sea level and also with that storm tides so worse cyclones, more intense, more storm surges, so that affects our coastal infrastructure. Secondly, an increase in extreme rainfalls, so in that one year to 100-year ARI type rainfalls which is what we use for design – so they're going to get worse those events. The advice does come with degrees of uncertainty and changes with time, and the graphic on the right illustrates why that's so. So climate modelling is still an emerging science and there's a long way to go there, but it is getting better. But what you see there on the right is some the emission scenarios that are are in the system and alignment through the UN and you can see how widely they vary – they just don't know what future missions really look like because there are so many variables. So they look at what they call represented concentration pathways, and that's what they use for the modelling, but look at the wide variation and that they haven't really got a clue what it looks like. So that's why this advice keeps changing with time and we've got to be so attuned to the latest science.

Just looking ahead, the RDM has evolved with time. In 2010 version, our climate change impact assessment was a point three meter increase in sea level and no increase in rainfall intensity. The 2015 version that we released last year, now it’s gone up to point six of a metre increase in mean sea level by 2100, still no increase in rainfall intensity. AR&R has very recently come out now and said actually there is going to be an increase in rainfall intensity and you've got to allow for that in your future planning, so many projects that have a design life of more than a few years you've got to start allowing for increases in rainfall intensity. Now TMR has always taken it’s advice on these issues from AR&R, and so we will need to amend their advice in the very near future.

Changes to hydrology. As Mark mentioned, AR&R which is the bible for flood estimation is being updated for the first time in 30 years, so this 87 version came out the first year I started as an engineer so it's it's a document close to my heart and these methods we've been using for my whole career but they are changing and there are some big changes coming. We're getting rid of the rational method effectively, which is quite a change because the RDM uses the rational method a lot – so we've got to get across that. There's a strong bias towards computer based methods including a technique called continuous simulation, which is a really exciting method and I'll talk about that in a moment. Then we're using, rather than a simple design storm, we're going to what's called an ensemble of temporal patterns so we'll probably look at ten to twenty storm patterns per design event to try and model that real variability that in design storms, rather than assuming some simple storm represents everything, so that's a real improvement in the way that we're going to be modelling floods. We are also changing from ARI, Average Recurrence Interval, which we've used forever, like a 100-year flood, to AEP Annual Exceedance Probability a 1% flood, reason being is that the community when you say the 100-year flood that, they just had one they automatically think I'll we're not going to get another one of these for 100 years and that's really, really dangerous because this is all about probability so that's why we're moving to a one-percent flood so that people understand it can happen in a year and you can even get multiple events in a year.

Now I talked about continuous simulation, I just want to give an example where we've used this on the Flinders Highway just recently and the power of this method. When you use a design event method and you're talking about a whole road link, so this is from Cloncurry in the west to Townsville in the east, 770 kilometres. When you use a traditional design event approach all it tells you is for individual crossings what the annual average time of closure is. For someone using the link, it doesn't help them with ‘If this crossing is closed, is that one closed and is that one closed?’ It can't help you with that. Continuous simulation can however.

It's a method where we model the climate for a hundred years or so and we model the entire link and actual rainfall patterns and there's an example of, so that's a snapshot of the right on one day. We run the models for 365 days times a hundred years of actual climate data and we model the flows at each and every crossing it’s as though we've had a stream gauge in them and then we’re able to crunch the numbers about and we work at the threshold flows when crossings close and we can get a whole picture of how the link performs over a hundred years of real climate and that's very powerful. What you then do is include the traffic volumes, including freight, you can work out the cost of delay and then you can work out the benefit stream when you come to do upgrades. So this is a very powerful method for allowing you to look at a whole link in a way that we've never done before and you can see why I'm excited about trying to apply this to the Bruce Highway and that's starting to get some traction which is great.

Now on the poor old rational method. We've been using this forever, the rational method, in Australia and there's a strong backlash from Queensland to its loss. The development industry is not happy and neither are a number of the council's – reason is that it's a simple cheap method to use and people don't want to give up. However, as academics will tell you, the problem with the rational method is there's very little actual data that supports it and the fundamental assumption is actually wrong which is about this time of concentration and constant rainfall. There's no such thing as constant rainfall as looking at real design event shows us, so you can see why there's a resistance to get the letting it go that the academics are right, that it's really not a very good method. Now QUDM is being finalised at the moment and it's likely to retain rational method because of this backlash, for certain applications not for all applications but certain applications, so we're actually going to get a schism it would seem. For the first time that you actually have QUDM and AR&R diverging on preferred hydrologic methods which is a shame, and the question is what should TMR do? Now we’ve traditionally always taken our advice on flood estimation from AR&R and I don't think we should be changing that, however, we've also got to remember that we're in Queensland and Queensland Urban Drainage Manual may take a different view so that's something we've got to think about. Back to Mike for urban drainage.

Mike Whitehead: Right, the urban drainage design process as Chris has just mentioned, we currently rely on the rational method for all their routine designs and it is suitable or has been deemed suitable up until probably now and recently the small and simple catchments – other catchments though however, do need more complex are computer based modelling and consideration because urban drainage is considerably more complex than rural drainage and that and can be very much a challenging for any designers and unfortunately it tends to change in time. The rational method I’ve said has been prescribed in QUDM which we refer to, however, the question will be is will we diverge away from that?

Just to give a little bit of a not insight into the complexity and apologies for a very old document, but that's what. Underneath the development lots there we have on the dotted line what would be the catchment area if it was undeveloped. So any rainfall falling within the catchment area, will drain to say a culvert or something like that down here and away and we could assess that. When developers come through however and they start to look at their lots, they will change the shape of the ground. So therefore we have to be aware of that because the dark solid line is now the new catchment area for it and that any water that falls and they will contribute to the outlet. And unfortunately we could potentially understand that and cater for it, but in another twenty years when a new developer comes in here and decides to put in a new shopping centre all or redevelop this to a higher density or something like that they could do further changes and maybe include this block here, they could also do things that all this section here we're going to put a shopping centre in but we're going to pipe the water out to there which means that no longer comes back to the other area. So that's why I mean the challenge for us is to be able to cater for this in time. nothing there so they can entrap . The other thing is it increases the area of impervious area sorry so that is when the rainfall hits it can't soak into the ground or it's not retained so it runs straight off, so by increasing number of roads,paved areas, rooftops etcetera that water potentially can run off. Now in recent years, larger developments have used retention basins or detention basins to try and mimic the old or previous flow because there has been conditioned to put on which is called no worsening and we expect that any work gets done doesn't change the current output of that, but that has been a challenge for us because it's it's often landed the department in some legal debates and arguments with developers,ministerials can get involved with it as well when people become unhappy, so it's a real challenge for us.

That's it. So now just a very quick overview again. It is complex and could take considerable time to go through the overall process but essentially what we’ve got to do is look at the development for houses to workout with the water coming from. Is it coming to a yard back here, was it being part to the front street? The street obviously collects the water and can actually act as a channel and we have streams and creeks throughout the urban area. Typically we have the curve in channel flow as the water flows along it. We then have pits and pipes that we put in and that's just take the water off the right service, get off the road and pipe it to where we needed to go. Typically then it will discharge into some creek or stream and then taken away. We do have the use of detention basins again to mitigate flooding and then it often goes off to receiving waters, whatever that may be and we have various pieces of infrastructure that we need to build to cater for that. And again, it's the no worsening because nobody wants water in their yard. People expect all over the years the flooding in the area has only been up to my back fence and if they see an event that pushes it up to the back door, they get very upset about it. Again, we can only use a design storm for our modelling to try and predict what's going to happen, we can't predict an actual storm, So the no worsening is the real problem for us and nobody wants water in their backyard so it will be a continual challenge for the department to get that and it's a continual legal exposure to us and how we deal with that.

The system that we predominantly use in an urban environment what we call the major minor system. The major, the minor system, sorry, is really just for the smaller events that we typically occur so they are ARIs 10 to 20 years. They typically will be drained off the road into a pipe system and then taken away. So there's very little impact of those on the on the community and on the road system. When we get the major drainage we go up to the Q50s and the Q100 events and largely those type of events most people don't really want to be out and about in them. So we actually allow the road itself to become part the channel. The underground system will put on, take some of the water and the rest of it has to go up above and away and t and that’s a method that we can use. One of things that sometimes gets forgotten, is when this system fails due to blockage through debris and rubbish and all sorts of things, the water that would go in there now has to go across here which will increase levels and that can cause flooding, which again then can be a bit of a backlash on the department. So there is some consideration there and of course what we do with extreme floods? Do we actually try and model the worst-case scenario and design for that even though the probability of it is probably low? It's an investment strategy for the department, we are limited in funds – what is the balance that we could achieve?

Lastly on this area, water sensitive urban design is important for us and it is emerging and it's dynamic in the research that’s being done and the benefits that can give us. TMR does have a role to play in it, we don't have any specific guidelines and have referred to the Australian, Engineers Australian’s guide Australian Runoff Quality. Unfortunately that document, and others, are more aimed at development, urban developments, not really geared to the linear infrastructure that TMR has. So one of our challenges is that we would like to work with our environmental colleagues to try and develop some better guidelines that’s suitable for TMR moving forward in this area. While rights do represent only a small portion of catchments, they are one of the bigger contributors to the water quality concerns, particularly when we’ve got roads with large AADT. As saif before, with the types of vehicles that we have on, the dangerous goods that they could be carrying – if anything happens that gets washed off into the road network.

Here’s a little bit of example in the urban environment this was taken back in 2008 in Mackay, Glennella Road. The above graphic there, the picture there is actually the water running down, now the system here hasn't, the underground system hasn't worked or is this full and obviously the major system is running here. There’s high velocities on that and again it was more of an extreme event so systems wouldn't really designed to cater for this, but this graphic here is after that's all gone that was what we were left with and have to go and repair. So again, it comes back to what is the department prepared to pay to try and minimize that for repair costs in the future or do we accept that and hope that doesn't happen? It's a challenge for us differently. Alright,back to Chris.

Chris Russell: So just a moment on creeks and streams. So this is the part of the system now where our analysis is extremely good. Typically these days we use what's called two-dimensional hydraulic models to model creeks and streams because we got fantastic Lidar or other survey available from most of the areas that we're looking at. A key issue, similar to the urban area, is typically try to achieve a no worsening in urban areas and in some of the semi-rural areas to avoid legal problems. Just to remind you though, that even widening a road can cause the impacts that can have an adverse effects on adjacent land holders and be difficult to mitigate in limited space – we just got to remember that that achieving a no worsening is always a challenge, even in some of the semi-rural environments, but the modelling methods that we've got a very robust and an example is a job at the moment that we're looking at which is Sandy Gulley Upgrade of the Bruce Highway, just north of Mackay. So 2D modelling has been used to assess impacts and mitigate those and so that's something that's being in work through detailed design right now – but the modelling that we adopt is very, very good these days, Intersection safety.

Mike Whitehead: The last section for the presentation. Intersection safety is something that's very important to all of us in TMR and even to the community, to try to save lives and reduce serious injury. Intersections are an area of concentrated accident because of the conflict points of people crossing each, also the area has a high demand for friction, people are accelerating, they're breaking, they’re changing direction – so the demand between the tyres and the road surface is much higher than anywhere else on the road network. Wet roads are where that friction drops dramatically, in fact, between one mil and four mils of water over the roads surface you'll see the biggest drop in available friction that we have. So even for that there, in small rainfall events most of your friction is disappearing rapidly and drivers aren’t aware of this and so their braking distances are greatly increased because they have to, they just end up sliding, particularly if they lock up. So drainage in the grading of the intersection must be compatible and we must try and get it right, As we said, also with intersections because of the grading and the cross falls etcetera of the road, because we've got crossing roads, we tend to flatten them also cars aren't feeling a bumpy experience going through intersections. When you flatten that off, the water can flow anyway because we need positive grade to drain the water, so that is where challenge is. We need to watch for the spread of flow from the kerbside so when we have the extreme events or even larger events the water will flow out onto the road and increase the depth of water we've got to drive through. There will be ponding and we’ve also got to be careful of that. In time, when the pavement starts to sag or to sink or rutting starts to occur – that starts to concentrate and capture water so we end up getting puddles where we never had them before. Again, that can add to the the potential safety issues of the thing, of the instruction. And as I've already mentioned, aquaplaning is not typically associated with intersections because of the lower speed environment, but with smooth surface and people not really having that legal tires etcetera, under heavy braking aquaplaning my occur. However as I said, skidding is something that can occur, and it’s something that we’ve got to try and cater for. So therefore grading of our kerbs around intersections needs to be carefully considered. We certainly need to look at all of our pits and pipes and alternative methods to try and get the water away. Once we capture the water, we want to get rid of it. We do have examples around where we’ve captured water and then through certain mishaps, I might say, the water actually then comes back out on the road and it's something which we got to really be careful of. Also another element of this which we're not going to really cover is the road surface itself and TMR has been actively involved for the last few years through various research and development projects to improve the quality of our road surfacing, particularly for anti-skid and high areas like interections, where we can service the road and improve the grip that's available, so that’s a positive that we’ve got there.

So having a look at a particular intersection, this is out on Beaudesert Road intersecting with the Granard and Rowena roads. It just gives an example of a typical urban intersection that TMR has to look after, multiple lines, large areas. This one is a particular bit of a problem because it is in a low-lying areas so does flood, but ignoring that, the amount of water that will fall on the in a typical afternoon storm has got to get away.We have a lot of truck movements through here, and again, the area in that section there because you've got crossing roads is very flat and so it's difficult for the water to flow or if it does flow it's very slow – so thicknesses can build up quite quickly. It is a challenge for us. So therefore, where we can we've got to put a series of pits and pipes in and various locations to try to capture that water and get the water away as soon as we can. Otherwise we end up with very long flow paths and again that can cause a problem. The other example that's here is the queuing that can occur. One of the things we have to look at and and work with their modellers is, to actually try and estimate what sort of queues have we got? So that in wet weather we can look at how far back are surfacing or drainage might need to go to get more water off so that when drivers see a queue and have to stop they can actually slightly do it. If we just do it traditionally, say to the end of the stop line, it means the cars back here doesn't have enough space to stop and then run into the back of a car in front. So again that is a challenge because, traffic is a quite variable, we've got these estimates of what the queues are, and then from there back for stopping distance the servicing and extra drainage we might have to do. That’s a challenge. The other one there is pedestrian crossings. We don't often think about it but water can actually knock a person of their feet. So where water is travelling around kerbs, we actually have a relationship of the velocity and the depth, and once it gets above point four, it can knock somebody off if they step into it. So we minimize the flow width, we minimize the velocity, so that the pedestrian access across here is a lot safer. Now there are challenges with people with mobility devices and how it affects them because a lot of them are electric and they don’t like getting into water, so do we have to go further with our standards? There's more work to be done in that area. So that just gives you a little bit of an example there, and that said, road surfacing in here typically, we probably have to surface quite a significant area with high skid-resistant surfacing and then maintain that over the time. So that’s our challenges. Alright, and just finally in this area, here we do make mistakes, we do have challenges. This particular one here, we're not sure whether it was a design error or a construction error, it’s never been investigated, but it does highlight how important drainage is and that we really do have to pay probably a little bit better attention. What we have here, this is actually T intersection, we've got a curve on the road here and this is another section coming into it. So in actual fact the cross fall across here super-elevated, so the road, this is the high part of the road, and the low part of the road is down the bottom of the picture. And here's a typical kerb and channel, it's catching water and it's meant to take it underneath the guardrail and off into a swale over there, but have a note that there's a puddle of water which means it can actually drain out, we've got something wrong there. So at the moment, that's the normal outlet, there’s ponding there which means that channel is almost sitting at capacity, even though there’s no flow init. So when we have a, and cross fall is that way. So when we have additional flow, you can go back here and can actually break out, and get back on the road. So this is an example where we’ve captured the water but through whatever the mechanism is, where now pushing it back out. That will increase the flow that's going across the water there with vehicles running around here, so again, depending on the speed environment, skidding off into the guardrail, potential aquaplaning problems – in this case here we're actually exacerbating the problem not solving it. So again, that’s our challenge to spend a bit more time, a bit more care with our drainage consideration, our drainage design and building it right, and unfortunately drainage is historically – because we don't see it for many years, it's buried under the road, unfortunately we don't consider it as well, or we just clean it there keep what's there and we keep going. When we have an extreme event, it's all highlighted, oh, there’s a problem but then it dies down we don't look at it again. So it is a probably a bit of a culture for TMR that we don't consider drainage as well as we should and particularly in the urban environment, but also equally in the rural which is most of their own network, we should take the time to look at it and consider it as much as we consider other elements of the road design and construction process.

Chris Russell: So just to wrap it up and go over what we thought were the key points. Firstly the new AR&R is bringing in some really big changes that are more onerous but will improve their estimation of real floods and as a hydrology person, I’m excited really by these new techniques, it is going to be more work, but they are a lot of better, they really are. Continuous simulation techniques can be used to help us get a really good understanding of the Bruce Highway if we want them to. I'm presenting to the steering committee for the Bruce Highway next month a case that we would do this and I’ll be showing them the Flinders and and hoping that we can move forward on that – even if it's only for one of the links, so fingers crossed on that. We need to amend their climate change advice again, so we've got we've got an amendment there to the RDM that we need to make and we need to keep monitoring that it'll keep changing. The Paris agreement will mean that the carbon pathways are revisited and so on so we've got to keep monitoring that. We need to decide what their position is in relation to the Rational Method and that's going to take a bit of thinking through all the implications of that. We need to be very careful with impacts in urban areas and maybe even mandate methodologies for certain cases. Internal staff training is also critical there, so our drainage courses and also Mike and I are working on a new one for people, for managers, to have think about bringing in some case studies of issues and where things have gone wrong. We think a key to helping lift our game there and of course the dot point that we've got put in there which is on the water quality aspects. We think it is worth doing some R&D, coming up with some criteria that are relevant to linear infrastructure, rather than the other development stuff that we're using – which is nice, but not that relevant. So, thank you.