In basin delineation and hydrological modeling, selecting the exact value in Flow Accumulation to identify streams is a critical step. The Flow Accumulation tool calculates the accumulated flow as it traverses down a landscape, which can be visualized as the number of cells contributing to flow into each cell. This accumulated flow can then be used to define stream networks by setting a threshold value.
Good morning,
to determine the threshold value I know of several ways. The first is to determine a reference stream, with a known source. This can be done by taking a field measurement or visually interperpetrating a shaded relief. Then read the Flow Accumulation value in the neighbourhood of the designated reference source. The second method is the trial-and-error method, but to avoid wasting too much time I recommend automation in the R programming language. A script automatically tests different threshold values and generates vector files, at the end you should choose the one that is closest to reality. In general, it is best to go into the field, but when this is not possible, consider drone inspections, reviews of data bases such as Opeen Street Map or local information sources, atlases and cartographic studies.
If you have any questions, please feel free to contact me, I can help as an R package developer.
Best regards,
Jakub
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