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Interpreting Confinement and Geomorphic change #34

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dsear opened this issue Sep 10, 2018 · 8 comments
Open

Interpreting Confinement and Geomorphic change #34

dsear opened this issue Sep 10, 2018 · 8 comments
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discussion Ideas for deveopment discussed amongst development team

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@dsear
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dsear commented Sep 10, 2018 •
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So I've made a start at visually (no real confinment stats here) interpreting the sequence of events during the Cumbrian floods and Desmond flooding for a couple of reaches. What seems to be key are:

  1. a sequence of constricted flood flow followed by rapid expansion - these occur because of human confinment/constrictions or natural ones, and/or when a valley suddenly changes direction.(Examples 1-4)
  2. A large erodible confining margin - hi violumes of sediment supply upstream of a flow expansion results in floodplain deposition and avulsion/channel widening (Example 1,2,4).
  3. Changes in channel direction between confining margins where the receiving margin (downstream) is erodible (Example 1)
    example1

It is the sequence that is as important as the magnitude of change - ie Constriction into expansion + erodible margin = alot of change.
Erodible margin into constriction probably = limited change (transfer of sediment) until expansion then = deposition..
Legacy Infrastructure is important for constriction of flow (Example 4)

I think we're trapping confining margins, erodible and non-erodible margins,anthropogenic confining margins. Are we getting constrictions? What to do about expansion/constriction. How to allocate these attributes in terms of proportionof a 500m segment of channel centreline?

example2
example4
@dsear
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dsear commented Sep 11, 2018

OK some more thoughts on the Confinment Project based on my Skype with Joe and subsequent musings....

TASKS for Geoprocessing (some of which already exist)...

  1. Split Channel Centrelines into 500m segments (sensu O'Brien et al in review) and at tributary junctions.
  2. Define ALL confining margins (Natural+Anthropogenic+River crossings)
  3. Define Erodibility of margins
  4. Calculate for each 500m centrline segement the following proportions:
  • Confinment
  • Anthropogenic confinement and Landscape confinement
  • Erodible / Non-Erodible
  • Area and Volume of erosion and deposition from GCD output (perhaps in future this could be Air Photo based).

Note that Resource Managers want information on the following risks:
A) Bank Erosion (farming issues and infrasrtucture)
B) Deposition on Floodplains (farming issues)
C) Loss of channel capacity (deposition in channel)
D) Damage to infrastructure (this could be a future input based on infrastructure layers - pipelines, cables, property etc).
NOTE: WE NEED TO ENSURE WE PROVIDE GUIDANCE ON WHAT IS PROBLEMATIC AND WHAT IS JUST WHAT A RIVER DOES - AND THUS IS PART OF A NATURAL ADJUSTMENT THAT HAS BENEFITS IN TERMS OF DOWNSTREAM DAMAGES.

The remaining issue is what to do about the variability in flood width (which is synonymous with valley width in narrow upland valleys during massive floods). It seems there are some critical changes we need to capture:

  1. Constriction - Expansion with large sediment supply in segment(s) upstream of expansion
  2. Constriction - Expansion with no immediate sediment supply
  3. Expansion - Constriction (with or without sediment supply).

It might simply be a question of auto-extracting 1:1000yr flood polygon widths at c. 250m points along the channel centreline, but the real trick will be how to identify the sequence. Since this is a proof of concept project we might use the Derwent and extract 100m widths (already done) and look at relationship between volume of erosion and deposition and the first differnce in valley width (ie downstream width minus upstream width), negative values are contraction valley width, positive values are expanding valley width. At 100m downstream intervals you get the Figure below

expansionfig1

This really does not reveal much control BUT this may be down to how we estimate expansion and contraction. I repeated for 250m and 500m interpolated centreline distances (should perhaps have totalled erosion and deposition over these distances?) and these were similar and equally showed no strong correlations. In effect what this is showing is that the presence and magnitude of erosion or deposition is a function of something other than simjple contraction and expansion as calculated this way....which suggests it may be more the presence of erodible confining margins (supply) as well as slope (power?) and some measure of confinement. In effect a (non-;linear) multiple regression model?! Welcome some thoughts on this one...

@Hornbydd Hornbydd mentioned this issue Sep 12, 2018
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@dsear
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dsear commented Oct 14, 2018 •
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Driver Variables required Datasets to derive them Relationship to GC Source
Unit stream power Q, S, b Hydraulic, hydrological models, DEM, channel boundaries. Positive High ω = > GC Magilligan (1992), Burrass et al (2014)
Bend Stress Rc/w Centreline, Bank lines Positive >Rc/w = >bank erosion. Burrass et al (2014).
Confinement / Constriction Confinement proportion DEM, Banklines, Centreline, Floodplain width Positive >Cf = > GC Pattison et al (2018)
Floodplain expansion Downstream/Upstream width ratio Floodplain confining margins, channel centreline Positive >Exp ration = > deposition change. Miller (1995)
Confiing Margin Erodibility BGS Drift or Solid geology classified into erodibility BGS drift, solid and confining margins and bank protection polylines Positive >erodibility of confining margin = >GC  
         

@dsear
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dsear commented Oct 14, 2018

These are candidate drivers of Geomorphic Change. We might create weightings for each and use these within a MCA framework to forecast presence of GC at 500m reach scale?
Burrass et al (2014) paper is helpful.
Woudl need to calculate flood power, and radius of bend curvature/bankfull width.
Thoughts.....

@dsear dsear closed this as completed Oct 14, 2018
@joewheaton joewheaton reopened this Oct 26, 2018
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So I've made a start at visually (no real confinement stats here) interpreting the sequence of events during the Cumbrian floods and Desmond flooding for a couple of reaches. What seems to be key are:

Nice work! I was missing this post because it was marked Closed. I just re-opened it.

  1. a sequence of constricted flood flow followed by rapid expansion - these occur because of human confinment/constrictions or natural ones, and/or when a valley suddenly changes direction.(Examples 1-4)

Exactly... so what seems to be key here is the transition from the special case of confinement on both sides (i.e. constriction) to a lower confinement value. This is really about all the bridge crossings, and its really the derivative of flow width as you move downstream. So confinement and constriction (or their derivatives with respect to distance) get at this, but its all about an expansion ratio and its highly sensitive on the length scale you calculate it at (i.e. if you segment your reach or river centerline @ these breaks and/or over the length scale of just the crossing). We should have a think about what we do here... We could focus @ road and railroad intersections and just deal with directly... Check out:

2018-10-26_130124

  1. A large erodible confining margin - hi violumes of sediment supply upstream of a flow expansion results in floodplain deposition and avulsion/channel widening (Example 1,2,4).

It seems like @Hornbydd is getting at this nicely now in #31 ?

  1. Changes in channel direction between confining margins where the receiving margin (downstream) is erodible (Example 1)
    example1

It is the sequence that is as important as the magnitude of change - ie Constriction into expansion + erodible margin = alot of change.

Agreed. We see same thing on the River Dee!

Erodible margin into constriction probably = limited change (transfer of sediment) until expansion then = deposition..

Good working hypothesis... I guess the question is... can we use the coarse confinement tool to identify these specific situations, and then use GCD data to test the prediction?

Legacy Infrastructure is important for constriction of flow (Example 4)

This seems like a relevant observation down the road. In other words, if we identify all the crossings, calculate the expansion ratio, and then the fair management question is are these actually pieces of infrastructure that are still in use or necessary?

I think we're trapping confining margins, erodible and non-erodible margins,anthropogenic confining margins. Are we getting constrictions? What to do about expansion/constriction. How to allocate these attributes in terms of proportionof a 500m segment of channel centreline?

This is the crux of the matter. I think we have two hypotheses... It turns out the ones related to expansions at the crossings (i.e. constrictions) are indirectly related to the downstream derivative of confinement... the others are related directly to confinement margins of specific types themselves (not just erodibility or type, but HEIGHT as well.

example2

This seems to me to highlight role of valley bottom width (in mega-floods we don't need to model hydraulics because we can use valley bottom width as proxy) related to active confining margins.

example4

This is really similar to what we see in GCD work and tracer work of bank erosion source producing deposition in next 1 or 2 downstream bars. Here, in megafloods, it is just in next one or two downstream, discontinuous floodplains...

@joewheaton
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OK some more thoughts on the Confinment Project based on my Skype with Joe and subsequent musings....

Again sorry for chiming in so late here.

TASKS for Geoprocessing (some of which already exist)...

  1. Split Channel Centrelines into 500m segments (sensu O'Brien et al in review) and at tributary junctions.

Yes, as default, but further split at top and bottom of all crossings and tributary junctions.

  1. Define ALL confining margins (Natural+Anthropogenic+River crossings)

YES! It seems like @Hornbydd is nearly there? Just how to make it automated off of nationally available OS data!

  1. Define Erodibility of margins

I think we don't mean 'erodibility' (i.e. how erodible a surface is). I think we mean source material (e.g. bedrock, terrace alluvium, alluvial fan alluvium, colluvium, floodplain, bedrock, etc.). Ultimately, we just want to take these categories, and understand what proportion of the active confining margin length is up against them...

  1. Calculate for each 500m centrline segement the following proportions:
  • Confinment

Yes, but then confinement by categories.

  • Anthropogenic confinement and Landscape confinement
  • Erodible / Non-Erodible

Yes, but first I would wnat to know confinement by the margin material and then lump back into this usesful summary)

  • Area and Volume of erosion and deposition from GCD output (perhaps in future this could be Air Photo based).

Yes, but this IS ONLY for hypothesis testing. To test hypotheses we have in Derwent and maybe Dee about these things.

Note that Resource Managers want information on the following risks:
A) Bank Erosion (farming issues and infrasrtucture)

We can look at whether or not this

B) Deposition on Floodplains (farming issues)

More to the point, how much deposition on floodplains is just natural processing, versus anthropogenically accelerated.

C) Loss of channel capacity (deposition in channel)

LETS NOT GO HERE. Its the wrong thing to focus on and our GCD LiDAR data is not good enough to get at it! It lets the narrative go back to the old 'conveyance' mantra of flood defense versus the better attenuation mindset.

D) Damage to infrastructure (this could be a future input based on infrastructure layers - pipelines, cables, property etc).

I have some things on BRAT and RCAT to show you on this. We should look at them.

NOTE: WE NEED TO ENSURE WE PROVIDE GUIDANCE ON WHAT IS PROBLEMATIC AND WHAT IS JUST WHAT A RIVER DOES - AND THUS IS PART OF A NATURAL ADJUSTMENT THAT HAS BENEFITS IN TERMS OF DOWNSTREAM DAMAGES.

Exactly.

The remaining issue is what to do about the variability in flood width (which is synonymous with valley width in narrow upland valleys during massive floods). It seems there are some critical changes we need to capture:

  1. Constriction - Expansion with large sediment supply in segment(s) upstream of expansion
  2. Constriction - Expansion with no immediate sediment supply
  3. Expansion - Constriction (with or without sediment supply).

I think we can do that...

It might simply be a question of auto-extracting 1:1000yr flood polygon widths at c. 250m points along the channel centreline, but the real trick will be how to identify the sequence. Since this is a proof of concept project we might use the Derwent and extract 100m widths (already done) and look at relationship between volume of erosion and deposition and the first differnce in valley width (ie downstream width minus upstream width), negative values are contraction valley width, positive values are expanding valley width. At 100m downstream intervals you get the Figure below

expansionfig1

This really does not reveal much control BUT this may be down to how we estimate expansion and contraction. I repeated for 250m and 500m interpolated centreline distances (should perhaps have totalled erosion and deposition over these distances?) and these were similar and equally showed no strong correlations. In effect what this is showing is that the presence and magnitude of erosion or deposition is a function of something other than simjple contraction and expansion as calculated this way....which suggests it may be more the presence of erodible confining margins (supply) as well as slope (power?) and some measure of confinement. In effect a (non-;linear) multiple regression model?! Welcome some thoughts on this one...

I need to chew on this one a bit more... lets Skype it.

@joewheaton joewheaton added the discussion Ideas for deveopment discussed amongst development team label Oct 26, 2018
@dsear
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dsear commented Oct 30, 2018 via email

@dsear
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dsear commented Oct 30, 2018

Hi Folks - I think this is the workflow for the next session on tihs project Duncan. Joe please edit this if unhappy. Aim is to get the variables linked to a segemented Centreline. See list of Drivers in previous Discussion Joe reopened and Table copied below
[2018_09_26_FRS17183_Summary of steering group feedback.docx](https://github.com/Riverscapes/ConfinementTool/files/2530916/2018_09_26_FRS17183_Summary.of.steering.group.feedback.d

@joewheaton
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@lauren-herbine and @shelbysawyer you might want to have a look at this old discussion.

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