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Pre-processing does not identify main stream channels in stream shapefile
I'm having some difficulty finding an appropriate value for "threshold flow accumulation" for the pre-processing module. I started with large values (10000, 3000, 1500, 1000) and found that my main stream channels were not being identified. (See picture below "stream1000".) I am comparing to an actual map of my streams.
Logically, a lower value would facilitate identification of more stream beds. However, even lower values are failing to identify main channels, despite identifying hundreds of nonexistent branches. (See picture below "stream100".) Note that for the upper stream, the model does not identify a continuous channel, and for the lower stream, only small parts of it are identified.
Note: blue = actual stream channels
green = predicted by toolbox
red = catchment of interest
As always, thanks for your ideas!