GIS/MEA582: Geospatial Modeling and Analysis

Flow routing and watershed analysis

Launch ArcGIS Pro and login with ArcGIS Online credentials if required. Select New> Map> Create New Project. Create a new project in your preferred workspace, in the instructions below we are using the default C:\Users\myname\Documents\ArcGIS\Projects\ folder.

Use your judgement to decide which maps to include in your report.

Derive flow pattern and streams from 10m NED

Fill the sinks in DEM:

In the Map tab, in the Layer group, click 'Add Data'
Browse to C:\Users\myname\Documents\ArcGIS\582data\ncrast.gdb
select 'elev'
'Ok'
In the Geoprocessing pane, search for and select the 'Fill' tool
Set 'Input surface raster' to 'elev'
Set 'Output Surface Raster' to 'Fill_elev1'
Click 'Run'

Compute flow direction:

In the Geoprocessing pane, search for and select the 'Flow Direction' tool
Set 'Input surface raster' to 'Fill_elev1'
Set 'Output flow direction raster' to 'FlowDir_fill1'
Click 'Run'

Compute flow accumulation:

In the Geoprocessing pane, search for and select the 'Flow Accumulation' tool
Set 'Input flow direction raster' to 'FlowDir_fill1'
Set 'Output accumulation raster' to 'FlowAcc_fill1'
Click 'Run'

Change the color table to something better - e.g. STRECHED yellow-green-blue, histogram equalized (Strech type) works well.
If the resolution of your screen is not good enough to see connected streams, zoom-in to see the detail.
Compare with streams digitized from high resolution orthophoto:

On the Map tab, in the Layer group, click 'Add Data'
Browse to C:\Users\myname\Documents\ArcGIS\582data\ncshape.gdb
select 'streams'
'OK'

Change color to red: how do the derived streams fit with the digitized data?

Derive drainage basins:

In the Geoprocessing pane, search for and select the 'Basin' tool
Set 'Input d8 flow direction raster' to 'FlowDir_fill1'
Set 'Output Raster' to 'Basins_fill1'
Click 'Run'

Derive flow path length:

In the Geoprocessing pane, search for and select the 'Flow Length' tool
Set 'Input flow direction raster' to 'FlowDir_fill1'
Set 'Output Raster' to 'flowlength'
Click 'Run'

Derive stream network and watersheds from 30m NED

First check whether we have sinks, if yes, fill them in.

In the Map tab, in the Layer group, click 'Add Data'
Browse to C:\Users\myname\Documents\ArcGIS\582data\ncrast.gdb
select 'elev_ned'
In the Geoprocessing pane, search for and select the 'Flow Direction' tool
Set 'Input surface raster' tp 'elev_ned' 
Set 'Output flow direction raster' to 'FlowDir_el30'
Click 'Run'

In the Geoprocessing pane, search for and select the 'Sink' tool
Set 'input d8 flow direction raster' to 'FlowDir_el30'
Set 'output raster' to 'sinks30'
Click 'Run'

In the Geoprocessing pane, search for and select the 'Fill' tool
Set 'Input surface raster' to 'elev_ned'
Set 'Output Surface Raster' to 'Fill_elev30'
Click 'Run'

Compute flow direction and flow accumulation

In the Geoprocessing pane, search for and select the 'Flow Direction' tool
Set 'Input surface raster' to 'Fill_elev30'
Set 'Output flow direction raster' to 'FlowDir_fil30'
Click 'Run'

In the Geoprocessing pane, search for and select the 'Flow Accumulation' tool
Set 'Input flow direction raster' to 'FlowDir_fil30'
Set 'Output accumulation raster' to 'Flowacc_fil30'
Click 'Run'

Extract streams from flow accumulation using map algebra

In the Geoprocessing pane, search for and select the 'Raster Calculator' tool
expression= Con( "Flowacc_fil30" > 10000, 1, 0 ) output=Streams_der30
Click 'Run'

Create stream links from the stream raster and derive watersheds draining into these stream links:

In the Geoprocessing pane, search for and select the 'Stream Link' tool
Set 'Input stream raster' to 'Streams_der30'
Set 'Input flow dir raster' to 'FlowDir_fil30'
Set 'Output' to 'Source30'

In the Geoprocessing pane, search for and select the 'Watershed' tool
Set Input d8 flow direction raster to 'FlowDir_fil30'
Set 'Input raster or Pour point data' to 'Source30'
Leave 'Pour point field' set to 'value'
Set 'Output' to 'Watersheds30'