Geospatial Modeling and Analysis

Flow routing and watershed analysis

Resources: ESRI virtual campus

Create the assignment working directory (folder) .\Hydro
Start ArcMap


Derive flow pattern and streams from 10m NED

Fill the sinks in DEM:
In ArcMap: add the raster feature layer ncrast.mdb/elev
Open the ArcToolbox
Select 'Spatial Analyst Tools->Hydrology->Fill'
Set 'Input' to 'elev'
Set 'Output Raster' to '.\Hydro\Fill_elev1'
Click 'OK'

Compute flow direction:

In ArcToolbox
Select 'Spatial Analyst Tools->Hydrology->Flow Direction'
Set 'Input' to 'Fill_elev1'
Set 'Output Raster' to '.\Hydro\FlowDir_fill1'
Click 'OK'

Compute flow accumulation:

In ArcToolbox
Select 'Spatial Analyst Tools->Hydrology->Flow Accumulation'
Set 'Input' to 'FlowDir_fill1'
Set 'Output Raster' to '.\Hydro\FlowAcc_fill1'
Click 'OK'

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:

In ArcMap add ncshape.mdb/streams

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

Derive drainage basins:

In ArcToolbox
Select 'Spatial Analyst Tools->Hydrology->Basin'
Set 'Input' to 'FlowDir_fill1'
Set 'Output Raster' to '.\Hydro\Basins_fill1'
Click 'OK'

Derive flow path length:

In ArcToolbox
Select 'Spatial Analyst Tools->Hydrology->Flow Length'
Set 'Input' to 'FlowDir_fill1'
Set 'Output Raster' to '.\Hydro\flowlength'
Click 'OK'

Derive stream network and watersheds from 30m NED

Set your workspace and scratch workspace to C:\path\.Hydro
Add ncrast/elev_ned
First check whether we have sinks, if yes, fill them in.
Spatial Analyst Tools->Hydrology->Flow Direction
input=elev_ned output=FlowDir_el30
Spatial Analyst Tools->Hydrology->Sink
input=FlowDir_el30 output=sinks30
Spatial Analyst Tools->Hydrology->Fill
input=elev_ned output=Fill_elev30
Compute flow direction and flow accumulation
Spatial Analyst Tools->Hydrology->Flow Direction
input=Fill_elev30 output=FlowDir_fil30
Spatial Analyst Tools->Hydrology->Flow Accumulation
input=FlowDir_fil30 output=Flowacc_fil30
Extract streams from flow accumulation using map algebra
Spatial Analyt Tools>Map Algebra>Raster Calculator
expression= Con( "Flowacc_fil30" > 10000, 1, 0 ) output=Streams_der30
Create stream links from the stream raster and derive watersheds draining into these stream links:
Spatial Analyst Tools->Hydrology->Stream Link
input=Streams_der30 flow dir raster=FlowDir_fil30 output=Source30
Spatial Analyst Tools->Hydrology->Watershed
input=FlowDir_fil30 Pour point=Source30 output=Watersheds30