QGIS - Channels and Drainage Basins with SAGA

[@jaimegonzalez5277]

Thank you for the tutorial, I have one question left. In the drainage basins and channel network tool, what does the threshold represent? Is it the number of water accumulation pixels? Is it a value in meters or in what unit is it? Thank you

[@koshishrajmaharjan]

When I try to use saga in qgis, it always ends up in 'The layers were not generated correctly'. Why? what should I do?

[@ChillMusikHardMusik]

Since when a Strahler-orde is negative? Why do you get such strange values?

[@stuartehamiltongmail]

since SAGA implemented this algorithm. the threshold describes the minimum Strahler order to initialize a channel. Here, the Strahler order is computed as follows: first, the Strahler Order grid is initialized with 0. Then, the DEM is processed top-down and for each cell it is evaluated which cells flow into it and which Strahler order they have. If two "streams" (here cells) of the same order flow into the currently processed cell, the cell is given a number that is one higher. If cells with different stream orders flow into the currently processed cell, the cell is given the higher of the two numbers. After the whole DEM is processed, you have a grid with stream orders that can be used to apply the threshold for channel initiation. Negative and zero cell values can be explained as follows: after all processing is done, just before tool execution stops, the order grid is processed once more by adding the following term to each grid cell: (1 - threshold) This assigns each cell an order, with the summit and ridges having the lowest order. I don't remember how this was implemented in SAGA 2.1.2, but in recent versions the NoData value range of the Stream Order grid is set to the "negative to zero" value range in order to mask these values in a map view.