Assistance in calculation of morphometric parameters

[Sandip Pantha]

Hello everyone. I am facing an issue determining the threshold value on flow accumulation for calculating stream orders on a watershed.  I  have initially placed a threshold value of 1000 upon reviewing some research papers. Is it correct or what determines the correct threshold pertaining to a particular watershed using a certain DEM? The watershed area is 4700 km2 and will be divided into multiple sub-watersheds. 

 Secondly, I am facing an issue with calculating the number of streams pertaining to a particular order.  Using the summarize tool on the attribute table overestimates the number of streams for a higher order stream which can be validated by visual examination over a smaller micro-watershed. Could anyone shed light on these aspects? 

[Jakab Andras - Gmail]

I am absolutely not an expert in this matter, but I found useful YouTube videos on this topic on many of the channels dedicated to QGIS.

Sandip Pantha <panthas...@gmail.com> ezt írta (időpont: 2024. máj. 18., Szo, 7:51):

Hello everyone. I am facing an issue determining the threshold value on flow accumulation for calculating stream orders on a watershed.  I  have initially placed a threshold value of 1000 upon reviewing some research papers. Is it correct or what determines the correct threshold pertaining to a particular watershed using a certain DEM? The watershed area is 4700 km2 and will be divided into multiple sub-watersheds. 

 Secondly, I am facing an issue with calculating the number of streams pertaining to a particular order.  Using the summarize tool on the attribute table overestimates the number of streams for a higher order stream which can be validated by visual examination over a smaller micro-watershed. Could anyone shed light on these aspects? 

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[Jonathan Quiroz]

Probably you are confusing "real" streams with what you can generate with a DEM. Flow accumulation is just a number that allows you to get more/less rivers because it is a "threshold". You may be getting streams that are not actually streams, but probably they get activated in a wet season. What I'd do is get some kind of river network from a water entity and try to match that if that's your target, if you don't have a target you can have as many rivers as the raster resolution allows

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