GIS for Watershed Modeling Exercise III

Use FlowDir as the input flow direction raster, save flow accumulation raster as FlowAcc.

• You will get flow accumulation grid. Notice, Cells with higher values are the ones that have low values on the elevation grid.

Compare the result with your manually calculated flow accumulation grid.

Drainage line processing

Now we will use ArcHydro to generate drainage line

1. Stream Definition
This step generates stream grid from stream accumulation grid.

From ArcHydro tool bar, select Tarrain Preprocessing – Stream Definition. Use FlowAcc as flow accumulation grid, Str as stream grid to be generated

About threshold:

• Flow accumulation threshold value defines the minimum or number of cells drainage area upstream necessary to define a stream.
Cell size = 100 x 100 m
Each cell represents 10,000 m2 in area.
If delineate the streams for a 10,000 cell flow accumulation threshold, the minimum drainage area upstream will be:
10,000 x 10,000 = 100,000,000 m2 or 100 km2

Use the default value (0.15) for this example.

Stream Segmentation

Stream segmentation generate a grid of stream segments from flow direction grid and stream grid created from stream definition processing. Input the dialog as following. FlowDir as the flow direction grid and Str as the Stream Grid. Output link grid will be Lnk.

You will get something similar to the following:

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