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You will now create a new point feature class to store the outlet point you just identified.

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

Delineating watersheds

Now you will delineate the watershed that flows to the outlet point.

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1. Click Tools from Analysis tab.
2. In the Hydrology toolset, double-click the Watershed tool.
3. For ‘Input flow direction raster’, select the FDR layer.
4. For ‘Input raster or feature pour point data’ select the Outlet layer from the drop-down menu.
5. For ‘Output raster’, rename the raster from “Watersh_FDR1” to “Watershed”.
6. Ensure your Geoprocessing pane appears as shown below and click Run.
   
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Notice that this is very close, but does not exactly match the boundaries of the subbasin you were originally provided from NHDPlus.

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Now that you have delineated the subbasin boundaries, you will generate flowlines. The number of flowlines that are generated will depend upon the flow accumulation threshold you select in separating a flowline cell from a non-flowline cell. For the purposes of this lab, you will select a threshold of 3000.

1. Click Tools from Analysis tab.
2. In the Map Algebra toolset, double-click the Raster Calculator tool.
3. Using the same clicking technique as before, enter the following equation: ("FAC" > 3000) & ("Watershed" > 0).
4. For ‘Output raster’, rename the raster from “fac_rasterca” to “Streams”.
5. Ensure your Geoprocessing pane appears as shown below and click Run.
   
   
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Again you should have a binary raster, where flowline cells are assigned a value of 1 and all other cells are assigned a value of 0.

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Generating stream links

Now you will separate your entire raster of flowlines into individual flowline segments as illustrated below.

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1. Click Tools from Analysis tab.
2. In the Hydrology toolset, double-click the Stream Link tool.
3. For ‘Input stream raster’, select the Streams layer.
4. For ‘Input flow direction raster’, select the FDR layer.
5. For ‘Output raster’, rename “StreamL_Stre1” to “StreamLinks”.
6. Ensure your Geoprocessing pane appears as shown below and clickRun.
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8. Symbolize the StreamLinks layer using unique values.
9. In the Contents pane, collapse the StreamLinks symbology.

Delineating catchment basins

Now you will delineate the catchment basin associated with each stream link. These catchment basins are similar to the subwatersheds you downloaded from NHDPlus.

1. Click Tools from Analysis tab.
2. In the Hydrology toolset, double-click the Watershed tool.
3. For ‘Input D8 flow direction raster’, select the FDR layer.
4. For ‘Input raster or feature pour point data’ select the StreamLinks layer.
5. For ‘Output raster’, rename “Watersh_FDR2” to “Catchments”.
6. Ensure your Geoprocessing pane appears as shown below and clickRun.
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7. Symbolize the Catchments layer using unique values.
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8. In the Contents pane, collapse the Catchments symbology.

Converting rasters to features

Now you will convert the Catchments raster into a polygon feature class.

1. Click Tools from Analysis tab.
2. Double-click the Conversion Tools toolbox à From Raster toolset à Raster to Polygon tool.
3. For ‘Input raster’, select the Catchments layer.
4. For ‘Output polyline features’, rename “RatsterT_Catchme1” to “CatchmentPoly”.
5. UncheckSimplify polylines.
6. Ensure your Geoprocessing pane appears as shown below and clickRun.
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7. Symbolize the CatchmentPoly layer using unique values with ID as the value field.
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8. In the Contents pane, collapse the CatchmentPoly symbology.

Now you will also convert the raster StreamLinks into a polyline feature class. While you could use the Raster to Polyline tool, you will instead use a tool in the Hydrology toolset, designed specifically for converting raster stream links into polyline features. The difference between the two methods is illustrated below.

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1. Click Tools from Analysis tab.
2. Collapse the Conversion Tools toolbox.
3. In the Hydrology toolset, double-click the Stream to Feature tool.
4. For ‘Input stream raster’, select the StreamLinks layer.
5. For ‘Input flow direction raster’, select the FDR layer.
6. For ‘Output polyline features’, rename the feature class from “StreamT_StreamL1” to “DrainageLines”.
7. UncheckSimplify polylines.
8. Ensure your Geoprocessing pane appears as shown below and clickRun.
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Calculating Strahler stream order

Now you will use the Strahler method to assign a flow hierarchy to the stream links as illustrated below.

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1. Click Tools from Analysis tab.
2. In the Hydrology toolset, double-click the Stream Order tool.
3. For ‘Input stream raster’, select the Streams layer.
4. For ‘Input flow direction raster’, select the FDR layer.
5. For ‘Output raster’, rename the raster from “StreamO_Stre1” to “StrahlerOrder”.
6. Ensure your Geoprocessing pane appears as shown below and clickRun.
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7. In the Contents pane, turn off all layers except for the new StrahlerOrder layer, so that its symbology is more apparent.
   
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Calculating zonal statistics

Now you would like to append this Strahler order to the attribute table of the DrainageLines vector layer, so that you may symbolize that layer using graduated symbols according to the Strahler order number. First, you will need to create a table indicating the Strahler order of each stream.

1. Click Tools from Analysis tab.
2. In the Spatial Analyst Tools toolbox, double-click the Zonal toolbox > 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 Geoprocessing pane appears as shown below and click Run.
   
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Adding a new field to an attribute table

Now you will create a new field in the DrainageLines attribute table to store the Strahler order number.

1. Open the DrainageLines attribute table.
2. At the top of the DrainageLines attribute table, click the Add Field button.
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4. For ‘Name:’, type “StrahlerOrder”.
5. Use the ‘Type:’ drop-down menu to select Short Integer.
6. Ensure your ‘Add Field’ window appears as shown below and click Save on top of  the main tab.
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Scroll all the way to the right and notice the new StrahlerOrder field has been added to the end of the table. All of the values are currently null, but will later be populated with the Strahler Order integers from the OrderTable.

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You are now ready to join the OrderTable to the DrainageLines layer based on their common identification fields.

1. Click the Table Options button and select Joins and Relates > Add Join….
   
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2. For ‘Input Join Field’, select the grid_code field.
3. For ‘Join Table’, select the OrderTable table.
4. For ‘Output Join Field’, select the VALUE field.
5. Ensure that your Geoprocessing pane appears as shown below and clickRun.
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6. Scroll across the table and notice that most of the statistics (Min, Max, Mean, Majority, Minority, Median) are the same and all contain the Strahler order integer, so it doesn’t matter which field you copy, though you will choose the MIN field for this lab.
7. In the attribute table, right-click on the StrahlerOrder field header and select Calculate Field….
8. Scroll down the list of ‘Fields:’ and double-click the OrderTable.MINORITY field and click Run.
9. Scroll down the newly populated StrahlerOrder field and notice the values of 1, 2, and 3 corresponding to Strahler order value. You no longer need join.
10. Again, click the Table Options button and select Joins and Relates > Remove Join(s) > Remove All Joins.
11. Symbolize the DrainageLines layer using graduated symbols based on the StrahlerOrder field.
12. In the Contents pane, turn on only the Outlet, DrainageLines, and CatchmentPoly, layers and turn off all other layers.
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FOR MAP LAYOUT TO BE TURNED IN

Create an 8.5 x 11 layout showing the vector catchment basins along with the stream links symbolized using graduated symbols according to their Strahler order and the outlet point that you used.

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