In this lab, you will be learning a variety of geoprocessing tools, with a focus on those within the Hydrology toolset. You will start by learning how to recondition a DEM file. You will then calculate flow direction and flow accumulation and learn how to generate drainage lines and catchment basins. Be sure to save your progress often. 

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1. Open Toobox.
2. Double-click the Data Management Tools toolbox à then Projections and Transformations toolset à then the Project tool.
3. For ‘Input Dataset or Feature Class’, drag in the Flowlines layer from the Table of Contents.

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1. In the Table of Contents, right-click the Flowlines layer and select Remove.
2. Repeat the above steps 4-7 for the Subbasin layer to produce a Subbasin_StatePlane layer.
3. Click Save on top of the menu bar to save the map document.
   
   

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1. Click the Toolbox icon.
2. Collapse the Data Management Tools toolbox.
3. Double-click the Conversion Tools toolbox à > To Raster toolset à > Feature to Raster tool.
4. For ‘Input features’, drag in the Flowlines_StatePlane layer from the Table of Contents.
5. Use the ‘Field’ drop-down menu to select the COMID field.
6. For ‘Output raster’, rename the raster from “Feature_Flow1” to “FlowlineRaster”.

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1. Click the ArcToolbox tab.
2. Collapse the Conversion Tools toolbox.
3. Double-click the Spatial Analyst Tools toolbox à > Math toolset à > Logical toolset à > Greater Than tool.

Remember that utilizing any tools in the Spatial Analyst Tools toolbox requires first activating the Spatial Analyst extension, which you have already done.

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1. Click the Toolbox icon.
2. Double-click the Data Management toolbox àRaster > Raster toolset à > Raster Processing toolset à > Clip tool.
3. For ‘Input Raster’, drag in the Reclassify layer.
4. Use the ‘Output Extent’ drop-down menu to select the Subbasin_StatePlane layer
5. Click ‘Use Input Features for Clipping Geometry’
6. For ‘Output raster’, rename the raster to “FlowlineReclass”.
7. Ensure that your ‘Clip’ window appears as shown below and click Run.
   
   
8. Open the attribute table for the “Reclassify” layer and note the ‘Count’ of cells with a value of 0.
9. Now open the attribute table for the “FlowlineReclass” layer and note the ‘Count’ of cells with a value of 0.

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1.  Click the ArcToolbox tab
2. Collapse the Raster Processing toolset and open the Raster Properties toolset à > Build Raster Attribute Table tool
3. Drag in the “FlowlineReclass” layer and click Run.
4. Now open the “FlowlineReclass” layer again and note that the number of cells that have been assigned a 0 have decreased to reflect the clipped geometry.
5. Remove “Reclassify”

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1. Click the Toolbox icon.
2. Within the Spatial Analyst Tools toolbox, collapse the Reclass toolset.
3. Double-click the Distance toolset à > Euclidean Distance tool.
4. For ‘Input raster or feature source data’, drag in the Flowlines_StatePlane layer from the Table of Contents.
5. For ‘Output distance raster’, rename the raster from “EucDist_Flow1” to “FlowlineDistance”.
6. Click the Environments… button.
7. For Processing Extent, use the ‘Extent’ drop-down menu to select Same as layer DEMft.
8. Use the ‘Snap Raster’ drop-down menu to select the DEMft raster.

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1. Click Tools.
2. Within the Spatial Analyst Tools toolbox, collapse the Distance toolset.
3. Double-click the Map Algebra toolset à > Raster Calculator tool.

When entering expressions in the raster calculator, your syntax must be exact, so though you could technically type in the equation below, we’d recommend entering everything by clicking the mouse, so you do not get any syntax errors (at least until you’ve learned the proper syntax).

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You should notice that the DEMRecon looks very similar to the original DEMft. To better understand the difference between the two, you will actually calculate the difference between their corresponding values.

1. Click the ArcToolbox Tools tab.
2. Double-click the Raster Calculator tool again.
3. Using the same clicking technique as before, enter the following equation: "DEMft” – “DEMRecon”.
4. For ‘Output raster’, rename the raster to “DEMDiff”.
5. Ensure your ‘Raster Calculator’ window appears as shown below and click Run.
   
   

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1. Click Tools from Analysis tab.
2. In the Hydrology toolset, double-click the Flow Accumulation tool.
3. For ‘Input flow direction raster’, drag in the FDR layer from the Table of Contents.
4. For ‘Output accumulation raster’, rename the raster from “FlowAcc_FDR1” to “FAC”.
5. Ensure your ‘Flow Accumulation’ window appears as shown below and click Run.
   
6. Turn off the Flowlines_StatePlane layer to better see the FAC layer.
7. Right-click the FAC layer and click the Symbology.
8. For ‘Symbology’, use drop-down menu to select Classify.
9. In the ‘Method’ drop-down menu to select Equal Interval
10. Use the ‘Classes’ drop-down menu to select 8 classes.Click the Classify… button.
11. For ‘Class Breaks’, double-click the numbers in the Upper Value column  and typethe following list: 100, 300, 1000, 3000, 10000, 30000, 100000. (Leave the final max value, 351408 as is.)Click OK.
12. Use the ‘Color Ramp’ drop-down menu to select the multipart color scheme.
    
    
    
    

Visually trace along the streams until you find the darkest path exiting the watershed. Notice that, according to the model you have just generated, the Buffalo-San Jacinto basin drains north into Lake Houston, instead of south into Galveston Bay. Look for the exact point on the map where this divergence is created. It is circled in the image below. A problem is that the topography in that area is extremely flat and, rather than a single well-defined channel, there are wide bodies of water connecting the bayous to Galveston Bay. Calculating the flow accumulation more accurately would require further editing the base raster so that the wide flat bodies of water are not treated as narrow flowlines. This example also illustrates how you must always double-check the results of your models to ensure they make sense. For the purposes of learning the remaining geoprocessing tools in this lab, you will continue with the existing flow accumulation model, as if it was correct.

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Zoom into the northern outlet point, as indicated on the image above, so that you can see the individual pixels.

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1. Click the Catalog tab.
2. Right-click the Lab1 HydrologyLab geodatabase and select New àFeature > Feature Class….
3. For ‘Feature Class Name’, type “Outlet”.
4. Use the ‘Geometry Type’ drop-down menu to select Point.
5. For Coordinate System, select Current Map.
6. Click Run.
7. On the Standard toolbar, click the Edit tab and click Create.
   
   
8. On the Create Features pane, select Outlet layer and click Point. Click à->.
   
   
9. In the Map Display, click the outlet pixel to draw a point there.
   
   
10. On the Editor toolbar, click Save.
11. When asked if you want to save your edits, click Yes.
12. Close the Editor toolbar and the Create Features tab.

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1. Click Tools from Analysis tab.
2. In the Spatial Analyst Tools toolbox, double-click the Zonal toolbox à > Zonal Statistics as Table.
3. For ‘Input raster or feature zone data’, select the StreamLinks layer from the drop-down menu.
4. Use the ‘Zone field’ drop-down menu to select the Value field.
5. For ‘Input value raster’, select the StrahlerOrder layer from the drop-down menu.
6. For ‘Output table’, rename the table from “ZonalSt_StreamL1” to “OrderTable”.
7. Ensure your ‘Zonal Statistics as Table’ window appears as shown below and click Run.
   
   

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1. Again, click the Table Options button and select Joins and Relates > Remove Join(s) à > Remove All Joins.
2. Symbolize the DrainageLines layer using graduated symbols based on the StrahlerOrder field.
3. In the Table of Contents, turn on only the Outlet, DrainageLines, and CatchmentPoly, layers and turn off all other layers.
   
   

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