Abby:
We are going to start this November Soil Network of Knowledge webinar. Welcome everyone. I am going to get on to introducing Sally
McInnes-Clarke who is from Office of Environment and Heritage where she has worked as a soil
scientist for over 20 years. Sally’s background is in soil and landscape
assessments or surveys or monitoring and soil health. In addition to this she currently manages
the NSW Soils Knowledge Network which is a group of retired citizen scientists and that
group aims to promote the importance of soils through knowledge and expertise and we’ve
actually had a view of those members present really fantastic webinars for us so they have
a facebook page and webpage stuff so it is good to look into that if you are interested. So today’s webinar, After the Fire, is an
ongoing project on soil loss recovery in the Warrumbungles National park and that draws
on Sally’s specialist skills as a member of the NSW and ACT burned area assessment
team, and they are looking at the post fire soil and hydrology risk assessment in the
park and that is what Sally is going to talk to you about today. Sally:
Good morning everybody. I’d like to begin by thanking Abby and Luke
for inviting me to give you this presentation this morning and I hope that this presentation
that you are going to see here today covers everything I hoped it would and that you all
get something useful out of it. So we will begin. As Abby said this is titled: After the fire
in Warrumbungle National Park NSW – an ongoing project in long-term soil loss and recovery. This project is important because the lessons
that we learn here will have a direct impact on the recovery program in the Warrumbungles. They have broad application for risks and
impacts and post fire monitoring of wild fires and also in the management of hazard reduction
burns. I would also like to acknowledge the contribution
of several people which have contributed to this project that includes Mitch Tulau, Robin
McAlpine, Charlie Carruthers, Xihua Yang and Bofu Yu and of course you know everybody in
the burned area assessment team, those that are here will notice that some of the photos
are familiar. So the purpose of this talk is to tell you
particularly about this project which is one of only several post fire recovery projects
which are currently ongoing in the Warrumbungles. Over the next 20 minutes or so we will cover
a bit about the fire, the rain event which happened, what I am doing with soil monitoring,
fluvial monitoring, erosion modelling and then I will finish up with what are our impressions
are so far but also that they are not conclusions cause as I said earlier this project is still
ongoing. So background for the fire; is that on the
12 January 2013 a fire began in Warrumbungle National Park. In one day it extended over 39,000ha in extreme
fire weather. It destroyed 53 houses and a wide variety
of other assets. The fire was contained at 56,290ha, 22,000
of which were actually in the park and the important thing here is that 76% of that fire
was at high to extreme burn severity. This slide here is just to give you an idea
of the location we are talking about. The study area is in North West NSW and Warrumbungle
National Park is just west of the town of Coonabarabran. The burn area was over 56,000ha, that small
map in the right hand corner up here is just to give you an idea of what that burn, how
big 56,000ha is actually and what that would look like if it was actually laid up over
the map of Sydney. These images here which you can see are just
a variety of images from the fire. This one on the top right here is actually
was a pretty famous photo it was actually taken by a commercial airline pilot flying
over the burn area. This one to the left is just indicating some
of the out buildings around Siding Springs which is of course the astronomy station. And the bottom two are some photos from the
burn area itself. This one here was taken from a 7 News helicopter
showing you, can you imagine standing there at the edge here looking at this fire coming,
extraordinary. The burn, the fire was so intense, this photo
is actually a very typical one of what it looked like afterwards. There were places in the park where there
was 100% consumption of fuel and you can see here that it was pretty intense, there is
nothing left of the litter although there are still some finer fuels left in this one
it is pretty typical. The other point to note here with this photo
is actually the absence of the erosion. This photo was taken about 2 weeks after the
fire began, the fire was actually was still going in some places of the park but in the
days immediately after the fire and the next sort of 10 days around 20-30mm of rain did
fall on this landscape and yet if you have a look there is actually no erosion. This is a copy of the burn severity map, this
is actually the original burn severity map, it has been updated since this. The yellow line is the park boundary and looking
at the statistics on the right hand side there that 70% of the burn was high to extreme so
that is the black and red areas and if you notice how concentrated they are in the centre
part of the park. And then in the afternoon of the 1st February
approximately 100-125mm of rain fell over the park in an area in the time of less than
40 minutes. The BOM data from the nearby weather stations
didn’t record anything like that amount of rain. In the top left corner there is a copy of
the radar from the BOM station out there and if you actually have a look here with Warrumbungles
this little black area up the top here, that’s where the Bungles are here and that is where
we are talking about. There is also a rain gauge at the Strathmore
Depot which is actually just down this road here, down to the right here. We based our estimate of 100-125mm on that
rain gauge but not matter how you look at it, it’s a lot of rain, and it is an enormous
amount of rain and it fell on a vulnerable landscape. So all that rain basically led to runoff and
huge amounts of runoff as you can see here. I should mention that these photos taken here
were taken by Dave Brill a National Parks Officer in the Coonabarabran Office, so he’s
taken all these flooding, these immediate photos are actually Dave Brills photos. There is some more run off for you, a landscape
that just doesn’t cope with all that rain and it all had to go somewhere. So that much run off leads to flooding and
there was, there was some intense flash flooding that happened around, that is actually the
depot, in the right, this is actually the rain gauge that we are talking about here. The next slide. This is behind the depot. That image there contains a picture of a shipping
container, and that was actually a fully loaded shipping container. It actually contained, I believe, helicopter
fuel. So that gives you some idea of the energy
in the water there. So all that water led to some erosion, I’m
sure that is not a surprise. This is actually a photo of the Wambelong
Creek just on John Renshaw Drive near the middle of the park. This photo here we can see that the flood
waters actually came to just below the road here, just along here and the energy actually
ripped off the concrete support under there road here, so it stripped it off here. This photo down here at the bottom left here,
Mitch Tulau took this photo, it comes from about 15km downstream on the western boundary,
past the western boundary of the park and there is a flood marker here we can see at
the top here and that measures at about 3, it hit 3.47m which is a significant flow. This is another photo by Mitch, it clearly
shows some of the scorch marks from the fire and then you can see just along here, and
there is this fresh exposed rock which happened after the rain. So this is in 40mins, this is the sort of
the erosion that happened on this site here and if we think about average soil bulk density,
1cm of soil loss across that area is going to be equivalent of 165t/ha of erosion. In this photo here using the ruler we can
see that the soil loss ranges from about 3-6cm on this rock which is in the range of 495-990t/ha/yr
which is anyway you look at it is pretty close to apocalyptic levels of erosion. So all that material if it has left the slopes
it had to go somewhere and it built up in the lower parts of the landscape. This is just a foot slope near what used to
be the old visitors centre and there is over 1m of material that has been deposited above
the original soil layer there. Another consequence of the rain was that first
order streams were scoured to bedrock, and the lower levels of those streams then commonly
contained debris flows particularly in the areas of the sandstone country which are underneath
the volcanic areas. The burned area assessment team made a series
of recommendations after the risk assessment and their recommendations were that there
would be increased frequency and intensity of runoff in all areas until the vegetation
in the park recovers. The sandstone areas below volcanic upper slopes
were at the greatest risk of sheet and gully erosion and particular hazards occurred where
drainage lines and roads cut across these areas, and both of those things have been
seen to be true. The other point that they made was that the
fire and subsequent severe rain was a massive event and the result lead to extraordinary
soil erosion, landscape change and long term damage to infrastructure and soil resources. Moving on to, that’s the background for
what happened with the fire and the rain so moving on to the recovery and what we are
doing out here. We have divided our project up in to 3 approaches. The first thing is to look at closed erosion,
closed soil erosion monitoring plots and which we are collect real soil loss data which is
quite an old fashioned approach to take these days, most people do a lot of modelling so
we are actually collecting data. We are actually monitoring the bed level change
in the creeks which drain into the area around Blackmans camping ground and the temporary
visitors centre. This was at the request of the National Parks
staff, they were really concerned about access to the catchment, there was sedimentation
which filled up the creeks, there was flooding so they want to know how long that’s going
to be an issue for them. The 3rd part of the project is the modelling
component where we are doing comparison of post fire remote sensing imagery before and
after the rain event on 1st February and then we will be calibrating these images using
real data from the soil monitoring plots. Then the next step will be to develop a time
series for long term soil loss and recovery. We have established 12 plots. We stratified them based on burn severity
and parent material. We reduced it to 3, burnt, unburnt, low-moderate
and high to extreme and then we kind of we bulked the parent materials into sedimentary
and volcanic. Unfortunately 2 of the sites the geology turned
out to be not what we planned for and then the burn severity map was updated from 4 classes
to 8, so we have had a drift from our original stratification but ultimately it didn’t,
I don’t think it makes much difference because we didn’t have a lot of choice about where
we were going to locate the plots. Access was severely reduced in the park, a
lot of the burn areas were consistent in terms of severity so we placed the sites where we
could and tried to achieve the best spread where we could. This one here is just to show, a location
of where our plots are, the 12 plots and their spread across the park. Coonabarabran to the east and we have got
sites, the first one here up at Siding Springs we have got 2 down here in the Strathmore
valley, our highest site up here at the TV tower, Gunneemooroo our driest / wettest site,
and they we have another 6 up through the main central valley and then the northern
fire trail. These shots just show you what some of our
plots look like. The plot area was 8m2, the slopes range from
between 20-38% with most sites are in the 20-30 28% slope range. Sediment erodes from the plots which falls
into the trough, you can see with this trough down here, and then it collects in the box
and then we collect it, we dry it, we weigh it and then use it to calculate t/ha/yr. The rainfall. Now the rainfall is a complex story and one
which we are struggling with. It is extremely variable across the park and
it varies both in spatial distance and it varies in its intensity and it presents the
biggest challenge we are facing in this project. The little table at the bottom is just to
show you, give an indication of, what the diversity of the rain in the spread is like. That’s just up from May last year to November
14, just those 3 periods there, the rainfall variability is enormous as you can see. We expect this, because a lot of the BOM stations
aren’t actually right in the park, they might be close to it but they might be on
the surrounding plains and with the terrain of a shield volcano being so different and
so high above the surrounding plains you have got to expect it to be different. On the positive side we have developed good
relationships with local landholders who are welcome to and willing to share and record
their trove of valuable rainfall data with us. This table here is just to give you an indication,
just to show you what cumulative erosion we’ve measured out there since June 14 till August
this year. The colours represent the various sampling
periods what I want you to see here is that the wide range of sediment collected over
a single period highlighting that variability in the rainfall volumes and intensity which
I was just talking about. Some of these sites are quite close to each
other they are within a few hundred metres of each other. For instance plots 2 and plot 10, here and
plot 10, they are quite similar on similar parent materials and yet quite different erosion
rates, likewise plots 7 & 8 are very close to each other but yet very different trajectories. This table is the measured erosion rates which
we have calculated for each of the plots and from June 13 till August this year the highest
erosion is at site 12 with 29t/ha/yr, down here. This site is on a sandy leptic tenosol with
a low fire severity, so did we expect this or not. The second site is at Gunneemooroo, it is
a red dermasol and rhyolite which was unburnt and yet look at the erosion coming off here. The third site, No 8, Scabion Hill, sedimentary,
conglomerate, it is a steeper slope, but you know it’s a high burn severity, so what
we can say about this erosion is that in the Warrumbungles erosion story is a complex thing
and what you expect to happen often isn’t what does happen. The ground cover is changing at each site
and we are recording fractional cover and we are using that to calibrate the remote
sensing imagery which will do that feedback for us as well. Part of the project is the fluvial monitoring
which I mentioned earlier. We have got 68 fixed points where we measure
relative changes in the height of the stream bed and over time we are seeing changes in
the sediment movement down the catchment. This is a graph of the middle branch of Buckleys
Creek from June to August. So June the red line and August the blue line. Overall there is a trend of bed lowering which
you can also see the shape of the bed is changing as well and there are slugs of material which
are moving down the slope. This actually records plus, we are recording
plus or minus relative change, it is not the exact elevation we are talking about here
and this is actually centimetres not elevation. So the next step in this project is, we are
trying to get a differential GPS to accurately measure elevation and we can identify residual
terraces in the bank deposits of the channel and then we can use the dimensions of the
channel to estimate total volumes of sediment which have been transported in this catchment
since the fire. We are doing stream cross sections as well,
which is looking at geomorphology and how that has changed. We have got 5 cross sections across the Buckleys
creek sub-catchment where we measure the height of the bed from a level string line between
2 fixed points. Again, the trend is a reduction in the height
of the bed and the sediment catchment over time, generally. It was reducing up here and then we come along
to August up here and back down again but it all depends on the rainfall and the intensity
and how much movement we are getting. So the Impressions, which are not conclusions
so far was that the enormous wildfire was a massive event. In terms of likelihood of its occurrence is
being recorded as being a 1 in 10,000 year event for the erosion. The result was extraordinary soil erosion
and landscape change. The second point so far importantly, is that
rainfall and therefore the erosivity and the energy in the rain to cause erosion is thus
far the dominant factor influencing erosion and recovery in the park and it is vital that
our, what we are doing with the rainfall we can then fill in some of those data gaps. There is 9 months to go for this project so
we have got a lot of data and we are embarking on seriously crunching it and seeing where
we are going. Which leads to the next point, was that we
missed it. The project began, the fire happened in January
13, the rain event in February, we didn’t actually get money and the authority to begin
this project until May the following year so there is 14 months where we are trying
to fill in that story. And the last point is that the data that we
collect at the erosion plots and the fluvial sites will inform the modelling and the long
term erosion in the next stage of this project. So this wraps up this presentation, I hope
that you have found this story about the way that fire and water movement through landscapes
to be an interesting one. Our findings will help inform the recovery
the park and management and guide management into the future. Personally though, my participation in the
Burned Area Assessment Team and then continuing in this post fire monitoring has forever changed
the way I feel about fire in the landscape. The force of fire and the scale of change
can’t be underestimated. Abby:
Thank you very much Sally, that was fantastic and very sobering. Now we have time for questions. Luke:
Fantastic talk thanks Sally. What hits me is are events like these, these
extreme events the ones that actually form the landscape that we see, these quite rare
events, are they the ones that you know really leave the landscape the way we see it today? Sally:
Thanks Luke. I think that, what we do know for certain
is that these sorts of scale events have happened before. There is plenty of evidence as you drive around
the park of old debris flows. And once you get your eye in and you recognise
what you are seeing, virtually every second drainage line is a, contains an enormous debris
flow. There are places in the landscape where whole
creeks have been diverted by flows. It is just, landscape change like this has
happened, they are a long time coming I guess, but we know that there has been so much erosion
happening out there, in the visitors centre, if anyone has been out there, there is a map
on the wall at the door which actually shows what the Warrumbungles used to look like hundreds
of millions of years ago, where the height of the landscape there was probably 2 to 3
times what it is now. And at the moment the top of Siding Springs
is about 1100 metres so imagine if it was about 3000metres what that would have looked
like. There are places too where there are alluvial
gravels underneath a bit of volcanic material a bit of trachyte at the top at the highest
point of the TV tower which can only have been there by recognising that that used to
actually be the lowest point in the landscape. The change out there over time has been enormous
and certainly there is a lot of carbon, there is a lot of charcoal in these debris flows. It is a project that Mitch wants to look at
more and we’ll hopefully get a time to get on to that in the next couple of months by
get some samples and sending them off to the lab and get some dates going and then we have
an understanding of the frequency of these sorts of events and because we can see they
definitely been, they have definitely occurred. Does that answer the question? Luke:
Yeah thank you Abby:
Rebecca has got a question Rebecca:
A really really interesting talk. I guess it’s hard to say because you don’t
have the data from immediately after the fire, if they didn’t have that massive storm there
is still presumably would have been erosion because the soil was so vulnerable and uncovered
from normal rainfall, would there? Sally:
Yes, it would have been. If you have got a landscape that has steep
slopes and no cover and it rains there is going to be movement. I think the key to what I was trying to say
earlier is that, the fire happened in February and there was 20-30mm of rain which was obviously
light rain, it was gentle rain and the landscape was so dry it just soaked it up like a sponge. So whilst on some of those photos I showed
initially when you were looking at these landscapes saying where is the erosion I don’t understand,
subsoil moisture was actually increasing and when the big event did hit the soils were
pre-saturated and ready to go. So they were heavier on the slopes and when
the rain came they were off and running. And to see so much soil washed away and leave
the catchment and basically its gone to Gilgandra now, but that treatment has been happening
for millions of years, that’s why the plains are like that, that’s why the mountain in
only a 1/3 of its original height. Rebecca:
Also I’m wondering in your soil plots the impact of vegetation returning on erosion
rates versus obviously you have got some very rocky areas that don’t look like they have
got a lot of vegetation potential. Have you got some interesting figures on that
at all. Sally:
Yeah we do. Every time we go out, I couldn’t cover everything
in my 20 minutes. We do measure ground cover every single time,
we taken photos of the landscape every time we visit, we usually time our visits based
around when there has been a bit of rain. We do have a series of photos showing how
ground cover is changing at each of the sites, and in some of them it is changing quite dramatically
and others less so. Of course the success of the vegetation is
an interesting thing as well. Initially there is basically rock and a few
baby acacias sticking up and then you come back 6 months later and the acacias are 3
metres tall and you can’t find the plot, we are wandering around going where is the
plot? It is here somewhere. So there is the changes that are happening,
they are all different, each site it is different things are happening at different times, so
I think, ground cover certainly plays a role, but growing ground cover I should clarify
too, because of course that provides vegetation rainfall interceptions, stem flow which moves
into the ground as opposed to rain that falls on bare soil rain splash impact which is like
that bomb going off. And rain splash impact we have seen is a significant
factor for a lot of these soils, when you get there the tray which is at the bottom
of the trough is just covered in dust and rain splash. So I think the story isn’t finished with
ground cover, because one of the sites that I named that has some of the worst erosion
at Gunneemooroo which was the unburnt site has no green material but actually has a lot
of litter all over it in the 80-90% of litter but only 5% of green cover that is actually
growing and other sites that seem to be doing so well it’s a complex thing and we are
talking to some of the plant people doing the plant monitoring to come out and have
a look with us and see what think might be going on. Possibly it’s related to springs and water
flow sub surface, position landscape, at this stage I haven’t got a trend for you to show
only we have got a lot of data and it is tricky. Rebecca:
Thank you Abby:
Thank you for the question Rebecca. Sally I have a question for you from Stephanie
Alt who doesn’t have a microphone so I will ask her question. She is interested in what she says here is
the development of the newly exposed soil surface and biological activity. So she says presumably a more biologically
active top soil layer has largely been lost in this soil erosion event and is there any
monitoring of that soil biology in that top soil and if so is it recovering? Sally:
Good question. I would agree that if we lost 1-5cm of the
surface soil pretty much across the National Park and the whole burn area, the biodiversity
that would have been lost was extraordinary. That said, we aren’t specifically monitoring
biological stuff other than the ground cover and in they we are monitoring cryptograms,
we are just seeing what % of the ground cover is green grass, dead litter, is cryptogram
or is it rock as a protection for the soil surface. That is not my expertise is the biodiversity
stuff, but it certainly would have made significant changes but yeah we aren’t monitoring it
at this point. Abby:
Ok, thank you. It would be interesting to know if National
Parks is looking into that too. Sally:
I don’t think they are. The other monitoring programs, are the water
stuff, there is biodiversity issues associated with the water and the water quality. There is fauna people, there is flora people
there is about 20 different projects all going on up there. The one person who might know something about
that is Yoshi who is monitoring sediment cores and looking at algae and pollen in from Crater
Lake, which is in sort of a this high elevation ephemeral lake in the top of the park and
he might have something to say about that. Abby:
I would like to take the opportunity to thank Sally for that presentation it was really
very interesting and all of you also to for participating today and Sally’s e-mail is
there on that slide at the end so everyone can see that and her phone numbers, so if
something occurs to you or you have another query a bit later on then you could do that. Please feel free to forward your invitations
on to anyone who you think might be interested for any of the webinars that you receive and
invitation for. Thank you very much. Sally:
Thank you Abby.