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um but what I've been looking at is how
bedrock rivers are transporting coarse

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sediment and I'm looking at a series of
rivers across Taiwan one of the things

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that you can see in these drone videos
is that the rivers are incredibly

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variable so we have these incredibly
coarse sediment this is up to 10 meters

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in diameter um and actually I'm gonna
come on scale on screen in a moment

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first scale oh there I am and so you can
see that there's spatial patterns in the

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grain size we also have patterns and
where it is relative to the banks and

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patterns relative to bedrock exposure as
we move down these different rivers so

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one of the things that we're interested
in is how these bedrock rivers are

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transporting sediment and are roading
the banks and eroding into the bedrock

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and we need to look across the full
range of variability and understand how

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is this changing over space and also how
is this changing over time so what are

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the variability in the spatial locations
of sediment transport capacity and also

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how is this changing with different
flows different flow events

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so the way

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that we're approaching this is with a
series of drone surveys so on the left

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is the drone survey from the field and
on the right is the photo realistic 3D

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model that we can actually make of the
exact same site so these are not quite

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exactly aligned but you can see that
these are highly photorealistic they're

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representing the full 3d geometry of the
channel we're able to pull out the full

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grain size distribution and actually see
what's going on here

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we can then go

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through these different rivers to
systems this is an animation of another

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3D model and we can move up and down
stream throughout these channels and map

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just like we were in the field we can
actually pull out things that are more

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difficult to map in the field this is
actually one that we've had to survey

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from a trail it's not possible to get
down into this Bank but we can go

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through and we can map lithology like we
would in the field we can pull out full

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grain size distributions measuring every
single grain that is in the channel we

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can pull out things that would be really
difficult to measure in the field like

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the high watermarks that we're seeing in
the channel breaks in that vegetation or

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that weathered bedrock
we can also pull out where that current

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water is and then we can see how this
changes at different points in the channe

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l so this is an example of the
kind of data density that we can get out

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of this so this is a one kilometer reach
in northeastern Taiwan and basically we

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have measurements of the bed slope
across the entire channel the high-water

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marks the channel width at both high
water and low flows. We can also measure

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the relative area of sediment both
coarse sediment and fine sediment in

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Taiwan fine sediment is like less than a
meter so different than other systems we

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can measure the distribution of boulders
throughout the system and what we're

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actually starting to see here is that
the spatial variability in these rivers

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is actually pretty much due to the rock
strength so we have variations in the

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lithology of bedrock that is exposed at
the surface and that is changing where

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you're getting wide rivers changing the
channel morphology so here for example

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the black schist are relatively weakest
rock is creating much wider river

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channels and that river channel it's
actually widening when we are parallel

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to the foliation Ingle of the bedrock
itself so you have structural

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variability that is really creating the
spatial variability in the system and

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that's actually corresponding to where
we're getting different sedimentation

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patterns so cool to see it change over
space but we can also measure it over

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time so these are photorealistic surveys
that have full 3d capability and so we

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can take a series of repeat surveys this
is further downstream of the same river

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where we have for repeat surveys and we
can actually compare them and see how

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these rivers change with different storm
events so we have a really unique data

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set this is about a 200 meter reach in
also in northeastern Taiwan where we

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have a range of grain sizes anywhere
from kind of 12 meter boulders don't

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have kind of fine sand and these
different surveys capture a range of

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different discharge events so between
2015 and 2017 we actually captured a

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Typhoon
um between 2017 and 2018 we had a

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high-flow year not a typhoon but still
high flow and then between 2018 and 2019

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there were relatively little storms so
we can start to compare this kind of

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data so we can fully map across these
reaches the different distributions of

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different grain sizes so this is between
2015 and 2017 that. that change we were

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capturing the typhoon event and we can
actually measure the differences in the

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grain size distribution throughout so
overall here we're not seeing a large

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change in the overall grain, grain size
distribution but we are seeing a lot of

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change in 3D so we can actually measure
aggradation and erosion at really high

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resolution and we're seeing meter up to
a meter of aggradation and a meter of

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erosion throughout this system and it's
non spatially uniform we can actually go

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through and measure every single boulder
that was in this channel and see whether

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it moved or not so about half of the
boulders in this system did move in this

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time period and while it is more likely
for the finer grains the 1 meter

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boulders to move we are seeing up to an
8 meter boulder moving between these two

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on two surveys if we move in from the
typhoon year to the stormy year we have

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less overall change we're seeing a net
erosion throughout the system

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we're transporting fewer boulders but
we're still transporting up to a 5 meter

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boulder in between that time but we're
seeing a really big change in the grain

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size distribution that we're actually
seeing in the channel so all the sudden

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we've lost a lot of our gravel and we're
increasing all of our other size classes

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so we're actually making the channel
more complex and we're reorganizing the

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channel and getting a lot more of a
rougher surface that we're seeing there

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and this is kind of that gravel is
eroding out in these patches all

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throughout the system between 2018 and
2019 where we have a relatively quiet

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year we don't see much change in the
overall bed state but we still see more

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of that gravel going away and the other
size class is increasing and so this

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kind of spatial pattern is showing that
complex to move these kind of flows with

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this wide range of grain sizes but we
can start to capture the full complexity

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both in the surface measurements and in
the actual full grain size distributions

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so overall this has showed that we can
use these kind of surveys to measure

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things over both space and over time and
see how the different sediment how

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sediment is able to be transported
differently wherever we are in the

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stream and we can use these repeat
surveys to see how it'll change over

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time so thank you for having me here

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I’m done