exercise 8 mapping the thickness of the rocky flats...

Geol 3050 – GIS for Geologists – Exercise 8

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Exercise 8 Mapping the Thickness of the Rocky Flats Alluvium and Reconstructing the Pleistocene Rocky Flats Paleogeography (with Spatial Analyst).

Due: Thursday, February 13 by the start of classGoal: Creating Rasters from point datasets, Raster Calculations Readings: Bolstad, Chapter 10 and 12

Datasets: Exercise 8.zip:

• Rftopo (GRID file) topography of Rocky Flats • Borings.shp (shapefile) Borehole data

• Main_rf_outline.shp (shapefile) Outline of the fan

• RectifyRFmap.tif (.tif image) topomap of the area

The data can be downloaded from http://geode.colorado.edu/~geol3050

Assignment:

Extensive shallow drill holes have been taken in several surveys at the former Rocky Flats plutonium plant, especially to the east of Highway 93, between Boulder and Golden. As you maybe noticed, the current morphology of the area is really flat and gently dipping east. However to the east of the Rocky Flats plant, several creeks incise the flat top surface. Why is this incision happening? The flat pediment seems to be a very hard surface with boulders up to 1m in diameter…

Beneath the present flat surface is actually an alluvial fan that came out of Coal Creek canyon during the Pleistocene. Its geometry is “fan” shaped and consists of high energy stream‐flow deposits. As is the nature of these streams, they searched for the lowest points in the landscape to fill up first, creating thicks, with coarser grained rocks at those places. The shallower places were not preferentially occupied by the streams and filled with the finer overbank deposits.

The finer deposits can erode much easier than the big boulders, which will create lows, where there used to be highs in the landscape. This is called inverted topography.

With the help of GIS we will map out what the paleogeography looked like before the Rocky Flats fan was deposited. There were streams, carving off the Pleistocene landscape, but exactly inverse to the situation now: where there were streams in the Pleistocene there are now highs, and where there were highs, there are now streams.

There is a hand out provided from Daniel Knepper (USGS), describing these findings, based on the GIS. In more detail: http://archives.datapages.com/data/rmag/mg/2005/knepper.pdf

http://geode.colorado.edu/~geol3050

http://archives.datapages.com/data/rmag/mg/2005/knepper.pdf


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The steps broken down:

1. Create a surface from your point (boring) file:a. Assess your data, realize your data are points (from borings).b. Interpolate the points to a raster surface, a GRID.c. Make a Layout.

2. Reconstructing the Paleotopography: Calculating with GRID’sd. Subtract the calculated thickness of the Alluvial Fan‐ GRID (point 1 b) from the current

topography (the DEM) to recreate the paleogeography.e. Create contours for your paleotopography.f. Create a Hillshade from your paleogeography.g. Make a Layout from your recreated paleogeography.

3. Display your Result in 3D: ArcSceneh. Add your layers to ArcScene.i. Add the correct Base Heights to each layer.j. Set the Vertical Exaggeration.k. Export your result to a 2D *.jpg file.

1. Create a surface from your point (boring) file:

A. Asses your data1. Download your data from the geosei server and Unzip your files.2. Browse your data with ArcCatalog and use the preview tab to look at your files3. Realize your “boring” data are points (bore‐holes).4. Open ArcMap5. Add all of your data to ArcMap: Make sure that the order of the layers is as follows:

• Borings.shp

• main_rf_outline.shp

• RectifyRFmap.tif

• rftopo6. Right click on borings and open the attribute table.7. Inspect the fields: we have a field for bedrock elevation at the borehole, a field for thickness of

the alluvial fan deposit and a field for the current ground elevation at the borehole.8. Symbolize your Boreholes numerically:

• i.e. you should set your Properties > Symbology > Quantities > Graduated Colors > Value:Thickness, so you can get familiar with the range of data.

B. Interpolate the boring points to a GRID9. Go to the Tools Menu >Customize> Extensions…10. Make sure that the following extensions are turned on:

• Spatial Analyst

• 3D Analyst


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We will first work with the Spatial Analayst 11. In the Geoprocessing menu at the top of the page, select Environment settings.12. Scroll down and extend the Raster Analysis Tab13. Under Mask, select main‐rf‐outline.shp

• The analysis mask makes sure we are only doing the analysis within our Fan outline (plus50 m buffer which is already applied for you, to make sure all data points areincorporated). We do not want to interpolate too far outside our data points, thereforethe buffer.

• When you interpolate beyond your data points, your analysis quality will decreaserapidly.

We will now interpolate our vector points into a continuous grid: 14. In ArcToolbox go to Spatial Analyst > Interpolation > IDW (Inverse Distance Weighted)15. Just use the defaults, but be sure to set the Z value field to THICKNESS and save your raster

in an appropriate spot! A semester long class on Spatial Statistics would be appropriate for a better understanding!Fill out the following values and be sure to save your output raster in your working folder:


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16. Your newly created raster (RFidw_th) will be added to your Table of Contents automatically.17. Make sure your outline (main‐rf‐outline.shp) is unchecked so you can examine the new raster:

Does it match your datapoints? Change the color of your raster into classes so you can compareto the classes of the datapoints. This can be under Properties > Symbology > Classified (match tothe classes you have chosen in step 8‐ you should use the same color ramp). You can also playwith the transparency.

18. Now that we have a raster surface of the thickness of the fan, we can also easily calculate thevolume (area x thickness) for each cell. We can do this by hand (as long as we know the cell sizeand how many cells we have, or GIS can easily calculate this for us:a. Make sure the 3D Analyst extension is activeb. Go to Arc Toolbox > 3D Analyst Tools > Functional Surface > Surface Volume

19. From Surface volumeInput Surface: rfidw_thOutput Text File: **browse to your Exercise 8 folder and save the file as IDWvolumeReference Plane: ABOVE

20. To open your table once the calculations are complete:

o Do this by opening Excel,o Select open from File on the main menu, browse to your foldero Files of type: All fileso Select IDWvolumeo Now you’ll be in the Text Import Wizard window

• Original Data Type: delimited; click Next• Delimiters: Commas; click next• Column Data Format: General; click Finish• Now your data is in a pretty Excel graph

21. Write down the volume answers for your layout


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22. Make a quick layout of your result for your write-up (what is the layout below missing?):

2. Reconstructing the Paleotopography: Calculating with GRID’s

For reconstruction of our Pleistocene Paleotopography, we will now SUBTRACT the thickness of the alluvial fan deposit from the present topography (DEM or Digital Elevation Model, called rf‐topo).

23. Go to Arc Toolbox > Spatial Analyst > Map Algebra > Raster Calculator.24. Subtract the GRID (raster) with the interpolated thickness of the alluvial fan (rfidw_th) from the

present topography and title the Output raster rf‐paleotopo and click OK.

Volume of the Fan = XXXXm2


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A. Create contours for your paleotopographyTo enhance visual effects you can create contours for your fan:

25. Go to Arc Toolbox > Spatial Analyst > Surface > Contour.26. Fill out the following parameters (input raster fr‐paleotopo):

• Contour 10m

• Base Contour Interval 0m

• No Z conversion 1 (needed for example from meters to feet) • Name your file paleo‐contours

B. Create a Hillshade from your paleogeographyA hillshade is a visual illumination typically calculated on your DEM, your topography. We will calculate it here for the paleotopography. It adds an effect of depth to your map and will help you visualize the holes on the east side of your map.

27. Go to Arc Toolbox > Spatial Analyst > Surface > Hillshade28. Fill out the following parameters (I kept the defaults, except for the new filename (Output

Raster: paleotopo‐hs). Save in your Exercise 8 folder!

29. Make sure the following layers are on in your Table of Contents. Appropriately symbolizecontours in order to compare with .tif contours…make sure these two sets are visible anddistinct.

• Borings (numerically classified by color on the field THICKNESS)

• Paleo‐contours

• Paleotopo‐hs

• RectifyRFmap.tif30. Turn the following layers on and off to look at the difference in topography between now (the

.tif image) and the Pleistocene:

• The points, the contours and the hillshade31. Note that the Lows from the Pleistocene are now Highs!

This is called inverted topography32. It’s a good time to make sure you saved your map!33. Make a layout with two dataframes:

• With just the .tif file in it


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• With the .tif file, the contour lines, the borings and the Pleistocene surface (paleotopo‐ hs).

34. Do this as follows:

• In the Layout View, right click on the active dataframe and choose COPY.• Right click on a blank spot in your Table of Contents and choose PASTE… there are your

two data frames. Or go to Edit>paste

• Choose the appropriate active layers (see above), use the scalebars from step 1 (makesure you saved it as another file (Export Map) as you need to hand in both Part 1 andPart 2 as a Layout). You don’t need legends at this time.

• Make it look like the following example:


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3. Display your result in 3D: Arc Scene

A. Add your layers to ArcScene**Keep ArcMap open.

35. Open ArcScene36. Add the following layers to the ArcScene project:

• Borings

• RectifyRFmap.tif (image of topo map)

• Paleotopo‐hs (the hillshade of the paleotopography)

• Rf‐topo (the current DEM/topography, uncheck it so it is not visible)• RF‐paleotopo (paleotopography values, uncheck it so it is not visible)

37. Go to the Layer Properties of Borings and RectifyRFmap.tif and paleotopo‐hs (so you need to dothis step three times):> Go to the Base Heights tab:

• Set the Base Height to rf‐topo for both (Borings and RectifyRF map layers):These layers need the current topography as base! Elevation from surfaces > Floating on a custom surface

• Set for the paleotopo‐hs Layer the Base Height to:RF‐Paleotopo (the old topography): This layer needs the PLEISTOCENE topography as base!

What happens in your “Scene”? Check that the three layers are elevated!

38. Again, go to the Layer Properties of the Borings Layer:> Go to the Extrusion tab:

• Click on Extrude features in layer…

• Then click on the little calculator next to the Extrusion value or expression box.

• Set the Extrusion value to –[THICKNESS], i.e. minus value of thickness (thicknessvalues were given as positive values, however, we are trying to subtract themfrom the topography/DEM).

• You may want to resymbolize borings for greater visibility.


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This will make the wells as long as the thickness of the alluvium.

39. Go to the View > Scene Properties. Set the Vertical Exaggeration to 5 and the background colorto a color of choice.

40. Use the navigation toolbar to zoom, spin and fly around (the following buttons are the mosthandy):

Zoom in, Zoom to Full Extent Zoom out, Pan and Navigate


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41. When you are zoomed to a nice representative 3D view, you can save your current snapshot asfollows (you only need to hand in one, with a sentence description about the view):

a. Go to File Menu > Export Scene > 2D and save your image as a .jpg file.b. Import it into your word document.

Rocky Flats‐ Present Day

Rocky Flats‐ Borehole data from below


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What you need to hand in!

1. Layout described at #22: Thickness of the Rocky Flats Alluvium with volume.2. Layout described at #33: Paleogeography of Rocky Flats.3. Exported 3D Display from ArcScene.

4. Compare your results to those of Knepper's publication (the link is at the start ofthis lab).

a. In particular, how do Knepper's alluvium thicknesses map compare withyours? If there are differences, provide reasonable explanations.

b. Why is it that the Pleistoscene valleys now make up the drainage divides(that is, inverted topography)?

c. Have a look at the history of Rocky Flats (the wikipedia page is fairlyaccurate: https://en.wikipedia.org/wiki/Rocky_Flats_Plant) What is oneinteresting or scary event/fact/consequence of Rocky Flats? Given thatthis plant is in the middle of our study area and on porous alluvium, give acomment on the potential for downstream (ground)water issues that mayexist today.

Paleogeography

exercise 8 mapping the thickness of the rocky flats...

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