Geography Reference
In-Depth Information
StrmOrder_StM—In which each stream is assigned an integer value that is an indication of its size,
in terms of the volume of water in it. The Strahler Method (hence the StM in the name) is used.
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StrmID—In which each stream is assigned an integer value that is unique within the study area.
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Finally, to show the utility of this information, we will consider that stream pollution has been discovered,
indicated by a raster called POLLUTION_PTS, from which we will determine SuspectAreas.
In summary, in this exercise you will create an elevation surface from a large number of points, generate
a flow direction raster, and then check it for sinks. You will also create a drainage network, assign stream
order to linear water bodies, and identify watershed basins.
Important note: The four input data files for this exercise (which are the shapefiles elevpts, fishnet72, and
the rasters ElevSurface2 and Pollution_Pts) will be found in
___IGIS-Arc_
YourInitials
\Spatial_Analyst_Data\Hydrology_Data_SA
However, you will put all the rasters you create in a file geodatabase Hydro.gdb.
1.
Start ArcMap. Make sure the 3D Analyst Extension is turned on and the 3D Analyst toolbar is
shown. Using the ArcCatalog sidebar, make a file geodatabase named Hydro.gdb in
___IGIS-Arc_
YourInitials
\Spatial_Analyst_Data\Hydrology_Data_SA
Refresh the Spatial_Analyst_Data folder (to be sure Hydro.gdb will show up later when you need it),
From the folder
___IGIS-Arc_
YourInitials
\Spatial_Analyst_Data\Hydrology_Data_SA
add elevpts.shp to the map. Examine its attribute table. SPOT is the elevation. How many
points are there? ______. What is the lowest? ________. Highest? ________. How many points
are there? ________
2.
Use the elevation point dataset to make a surface raster of elevations:
Find the Spline tool (in
ArcToolbox > 3D Analyst Tools > Raster Interpolation). Start the Spline tool. The Input points
should be elevpts. The Z value field should be SPOT. Accept the default cell size. In the Output
raster specification, browse to the Hydro.gdb file database, in the Hydrology_Data_SA, folder
and type ElevSurface for the name. Accept the other defaults. Click OK. ElevSurface should be
added to the map.
Examining the Surface with Various Spatial Analyst
and 3D Tools
3.
On the 3D Analyst toolbar click the Create Contour icon. Then click a cell near the center of the
map. You will see a line that represents all the locations you could visit without changing your
elevation from the selected cell. If you tap Delete on your keyboard that closed line will go
away. If you click elsewhere on the map you will get another contour line. Make several more
contour lines.
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