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Page1of15 DEMCONDITIONING

Program: Conse rvation pplications of LiD R Data http://tsp.umn.edu/lidar

Funding: EnvironmentandNaturalResourcesTrustFund

Module: Hydrologic pplications

Instructor: SeanVaughn,DNRGISHydrologist(FundedbytheCleanWaterFund)

Exercise: DEM Conditioning

Objectives

Introduce Digital Dams

Apply a TPI grid for hydrography identification within a 3 meter LiDAR derived DEM.

Demonstrate the use of the Topo to Rastertool for hydrologically conditioning a DEM for theremoval of Digital Dams.

o The utilization of the Topo to Rastertool is one method. It works exceptionally well,

and it is readily available within the ArcMap Toolbox. There are several othermethods for accomplishing the removal of dams including but not limited to:

DEM subtraction at digital dam locations. DEM to raster point conversion with specific point removal followed by a point

to DEM raster conversion. AGREE application via ArcHydro Break line utilization within the LiDAR point cloud.

AMUDEM software (http://fennerschool.anu.edu.au/research/publications/softwaredatasets/anudem)

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Setup

Exercise & Data Location:

A link to the data for this exercise is available in the same place where this document is posted.

In this document, the root folder is indicated as %root folder%\= Flash_Drive\_sevaughn_LiDAR\DEM_

CONDITIONING

1. Map a drive to the exercise contents:

a. Use the Connect To Folderbutton to map a drive to the location of the exercise files.

In this example, they are on a Flash Drive %rootfolder%.

Name: %rootfolder%Location: (%Flash_Drive%)\_sevaughn_LiDAR\DEM_ CONDITIONING

2. Open the ArcMap.mxd project for the exercisenamed DEM_conditioning.mxd.

Name: DEM_conditioning.mxdLocation: %root folder%:\dem_condition_PROJECT

3. Check your Geoprocessing/Toolbox Environment settings.

Discussion / Review:

This ArcMap project has been set up for you. This ArcMap project should have all ofthe Environmental Settingsestablished. A quick review of the EnvironmentSettingsshould contain entries familiar to you and suited to this exercise.

OR

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a. Workspaceshould point to the dem_conditioning_DATAfolder.

b. Scratch Workspaceshould point to the dem_conditioning_SCRATCHfolder.

c. Processing Extent= dem03(As Specified Below)

d. Most importantly, make sure that Snap Rasteris set to dem03.


After you've run a tool, you may find that the output isn't written where you expectperhaps you made a mistake when entering the output name, or you've just forgottenwhere it was written. If this is the case, open the Results window; it will contain arecord of the tool you've run along with its input and output datasets.

xc

4. Turn offall layers in the Table of Contents.

5. Turn on dem_03and dem03_hlshd.

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6. Set Displayand Symbologyfor dem03.

Display Tab

Resample during display using: = Bilinear Interpolation (for continuous data)

Contrast: = 0%

Brightness: = 0%

Transparency = 55%

Symbology Tab

Show: = Stretched

Color Ramp: = {your choice}

Stretch Type: = Standard Deviations, n: = 2

Statistics: = From Current Display Extent

7. Review the DEM. Locate the intersection of the ditch and road and the resulting DigitalDam in the area identified below.

8. Save your ArcMap project DEM_conditioning.mxd..

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Raster Hydrology ComparisonStandard ESRI raster processing for hydrologic applications requires that all cells within theDEM contribute flow. Meaning, all cells contribute water to an adjacent cell. This isaccomplished by creating a filled DEM. In such a raster, all cells that contain an elevationvalue lower than their neighboring 8 cells (sinks) are filled to the elevation at which theywill outlet water to an adjacent cell of lesser value.

1. Turn offall layers.

2. To save time the Fillprocess has been run for you. Turn on the raster named fill1_hlshd tosee how the grid was filled to overtake digital dams on the landscape.

3. Turn on the reclassed flow accumulation raster named rcls_flwac150.

Discussion / Review: Raster flowacc_flow1is a flow accumulation grid built from the filled DEM.

The raster rcls_flwac150is a reclassification of the raster flowacc_flow1. Itrepresents all grid cells that have a flow accumulation or upstream contrition of 150grid cells or more.

Notice how the flow has shifted locations around the DEM to flow over the digitalDAMs at areas away from the actual location of the conveyance feature (ditch) asidentified in the previous steps.

Thislargeflatarea

representsafilled

(raised)depressionon

thelandscape.

Weknow

this

is

not

supposedtobean

impoundment.

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4. Turn off fill1_hlshd and turn on tpi_cir1 raster.a. Place tpi_cir1 under rcls_flwac150 if it isnt already,.b. Zoom into the lower-center part of the raster.


. Notice how much different the reclassified flow accumulation (rcls_flwac150) isfrom the hydrography represented in the tpi_cir1raster.

. This demonstrates the effects of Digital Dams on hydrologic modeling using

unconditioned DEMs.

5. Now that you have a better idea of what Digital Dams are, turn offthe rcls_flwac150raster.Take a moment to pan around the DEM, notice that every road, driveway and field approachproduces a digital dam.

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Topo to Raster InputsTo ensure water will flow within the DEM properly we must hydrologically condition the DEMby breaching digital dams. In this exercise, we wont correct/breach all the digital dams inthe exercise dataset. Instead we will focus on some previous identified digital dams (withinyellow boxes) for instructional purposes. We will be using the Topo to Rastertool for theprocessing but first we must prepare some inputs to the tool.

1. The Topo to Rastertool runs on point and contour data. We will create a dataset of pointsfrom the base DEM [DEM03] using the Raster to Point toolfor our input to the Topo toRastertool.

a. Use the Raster to PointToolto create a point file out of our base DEM [DEM03]

ArcToolbox Conversion Tools From Raster Raster to Point

b. Name it dem03_pnt

Location: %root folder%:

dem_condition_DATA\dem03_pnt.shp

2. Turn offall layers in the Table of Contents except for tpi_cir1.

3. Turn on the digl_dam_breach_loc dataset.


This dataset represents 5yellow polygon rectangleswhere you are going to create breaches to cutthrough the digital dams. Make sure you zoom out tolocate all five areas.

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4. Load the contours (contours_2ft) from theAncillary_dataFeature Dataset.

Location: %rootfolder%:\dem_condition_DATA\DEM_Conditioning_geodb.gdb\Ancilary_data

5. Create a new polyline shapefile.

Location: %root folder%:\dem_condition_DATA\

a. Name the new dataset dam_breaks.

i. You will need to set the coordinate system to NAD 83 UTM Zone 15N.

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b. Create a breach represented as a short arc at each of the 5locations identified bythe digl_dam_breach_loc layer.

Discussion

To breach the digital dam, these short breach arcs should start slightly before andend on the opposite-downstream side of the digital dam (road etc.). The arcs must

point downstream so you need to digitize in the downstream direction. Visuallyinterpret dem03 and the contours by zooming out to full extent to ensure you see thedownstream direction of the landscape. This will help ensure that your arcs aredigitized in the downstream direction. Zoom into each of the 5 locations (yellowboxes) at a scale of approximately 1:2,000. Digitize the breach arcs as perpendicularto the digital dam as possible while staying inside the watercourse (dark area of TPI).

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Topo to RasterWe are now going to use the Topo to Raster Toolto breach five designated digital dams creatinga partial hydrologically conditioned DEM for hydrological analysis in a GIS.

The Topo to Rastertool is an interpolation process design to create hydrologically conditionedDEMs based on its parent product ANUDEM-algorithms developed by Dr Michael Hutchinson atthe Australian National University ( http://fennerschool.anu.edu.au/research/publications/softwaredatasets/anudem). The current version of ANUDEM used in ArcGIS is 4.6.3.

1. Open the Topo to Raster Tool. Topo To Raster operates from within both the 3D AnalystTool Set and the Spatial Analyst Tools.

a. . Spatial Analyst Tools Interpolation Topo to Raster -OR-3D Analyst Tools Raster Interpolation Topo to Raster

2. Setup the Topo to Rastertool dialog.a. Load the dem03_pntpoint file and select PointElevations from the internal drop down

menu.

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b. Set the Fieldand Typerequirements within the internal dropdown menus (see nextseries of graphics). This functionality is activated by left clicking in the box within theFieldand Typecolumns and making your selection from the drop down lists.

Discussion / Review: The GRID_CODEis a field in the point file that carries the elevationvalue for each cell from the DEM which will then be assigned to each point in theinterpolation process executed by the Topo to Raster tool.

c. Add 1.) dam_breaksand 2.) Boundary layers to the dialog from the dropdownselection menu. Fill in the feature Typeoptions for the other 2 Feature Layers so themenu looks like this:

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d. Define the output raster to be located in the iteration_1folder and name the newraster dem03_hydro1.

Location: %root folder%:\dem_condition_OUTPUT\iteration_1

Discussion / Review: The hydrologic conditioning of DEMs is an iterative process. Theexecution of the correction technique is run several times adding more digital dambreaches each time until the DEM is demonstrating sufficient flow such that thehydrology of the landscape is represented and meeting the objectives of the task atthe necessary scale. The outputs of these iterations are best managed by the use offolders with consecutive iteration numbers (iteration_1, iteration_2 etc.).

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e. Fill in the rest of the menu to look like this:

3. Change the Current Workplacein the Environment Settings at the Tool Levelto thedem_condition_OUTPUT\iteration_1 folder (see arrow and graphic above).

Location: %root folder%: \dem_condition_OUTPUT\iteration_1

Discussion / Review: Notice that for this exercise we have selected all the defaultvalues. This keeps the setup simple for this exercise. You may find it to beadvantageous to change these setting in your future work with different datasetinputs. Additional information can be found within the ArcMap help.

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4. Hit OKto run the Topo to Raster Tool. Thisshould take 1 to 5 minutes to run depending onthe CPU capabilities of the lab machines.

5. The newly corrected DEM should have loaded into your Table of Contents. Change theSymbology to a Stretcheddata display (if it isnt already).

6. Create a Hillshadeof the new hydrologically conditioned DEM named hydro1_hlshd (youcreated a hillshade in the DEM DISPLAY Exercise which you can use to reference therequired steps for this task). Compare this new Hillshade to the original base DEMHillshade and the Filled DEM hillshde at the locations of your dam breach arcs.

Digital Dam Breached Digital Dam(hydrologically conditioned)

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You should now be able to see that the digital dams were breached allowing water toflow through the barriers.

7. This exercise is complete. Depending on how the course and day progressed you mayhave extra time. Please use any remaining time to experiment with the data, make a TPI ofthe hydrologically conditioned DEM and/or ask any questions you may have.

___________________________________________________________________________

Documentversion:June2013

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