11

From your image, I guess that the red streams (labelled "3") are flowing into the lake and the green streams (labelled "4") are flowing out. Thus, from a topological point of view, your stream network is equivalent to (excuse my poor drawing skills): I highlighted the "lake" node with a big blue point. You can see that you have a loop inside your stream ...


7

Algorithms for performing stream network analysis all work in a similar way. These tools will use the D8 flow direction (Fdr) grid to navigate through a defined raster stream network (Str) using the network of flow paths defined by the D8 flow direction. Essentially what a link classification tool will do is scan the raster, usually starting from the upper-...


5

I wrote a detailed answer to another recent question regarding extraction of streams from DEMs here. However, the gist of it is that when you extract a stream from a flow accumulation raster (upslope area) you are effectively saying that there exists a geomorphic threshold that relates the amount of discharge (upslope area is used as a surrogate for ...


4

I would like to defend RivEX and what its capable of. I have to admit I have a vested interest as I'm the developer behind it. Some very clever people (not me!) developed an algorithm that could compute Strahler order and RivEX uses this algorithm for assigning Strahler order. It's very fast and can handle highly threaded networks. I've thrown networks in ...


4

I don't believe that you can perform a true Horton stream ordering using ArcGIS's Stream Order tool. However, the Horton stream order is essentially the same as the Strahler stream order, except that after the ordering, you need to replace each of the Strahler order values along the main trunk of the stream with the order value of the outlet. So if you can ...


3

Out of curiosity I downloaded the NVS stream tool and ran it on a vector river network that has loops and compared the Strahler order generated by this tool with the Strahler order computed by RivEX. The algorithm used by the NVS tool is slower (not really a big problem) but more importantly it is not robust when it is dealing with river networks that have ...


3

You might want to try running Fill Sinks. This is available using SAGA via Processing. There may be GRASS versions too. I didn't see any mention of it in the tutorial you linked to, so it's worth a look. What this does is make tiny adjustments to each cell's height, so that it maintains a minimum downward slope to its neighbours. That way, when you run the ...


3

To create the raster stream network you first threshold a flow accumulation raster, likely using the Raster Calculator or the Con tool. You're right that this will create a Boolean streams map of 1's and 0's. To break the streams raster into the various stream segments (links or tributaries) you would use the Stream Link tool using the same streams raster ...


2

You don't say which GIS system you are using! You can dissolve lines using the Dissolve tool in ArcGIS. Make sure you tick on unsplit lines option.


2

I have calculated stream order with the SAGA GIS module. You can read about the modules here: http://www.saga-gis.org/saga_module_doc/2.1.3/ta_hydrology.html All this assumes you have an elevation model in GeoTIFF. In order to get that working you need to install QGIS with the OSGeo4W installer and make sure SAGA GIS is checked for install: Then you have ...


2

I gave a fairly detailed description of how these types of stream network operations work in my previous answer here. But if you're looking for the exact algorithmic solution for how stream cells are recognized in the stream link raster and how confluences (junctions) are spotted in the network then you may look at the following source code as examples: ...


2

It sounds like you want to come up with your own threshold for determining streams based on the Flow Accumulation Values. You can do this using the Raster Calculator in Spatial Analyst (under Map Algebra in 10.x versions). You would use a Con Statement to create the streams like this (using 200 as an example threshold) ... Con("FAC" > 200, 1, 0) If you ...


2

You are looking for r.stream.snap tool, i think. r.stream.snap - Snap point to modelled stream network. Input can be stream network, point vector map with outlets or outlet coordinates. It's a special module that needs to be installed via g.extension As a workaround if that doesn't work, other software could do it. For example, via QGIS interface or ...


1

The GRASS GIS Addon v.stream.order computes the stream order of stream networks stored in a vector map at specific outlet vector points. It offers Strahler's stream order, Shreve's stream magnitude, Scheidegger's stream magnitude, and Drwal's stream hierarchy. Likewise, there is the r.stream.order addon.


1

I have come up with an approach: Create a point layer with points for each vertex in the stream network layer Buffer each vertex a (small) desired amount (I arbitrarily chose 10 metres) Run intersect and create points as the output, this will create a series of points where the buffer intersects the stream layer at the setback amount. Identify which points ...


1

Generally there are three main steps to creating a channel network. Hydrologically controlled DEM Catchment Areas Channel Network In more detail Hydrologically controlled DEM Use one of the Fill Sinks (eg Wang&Liu) algorithms to create a hydrologically controlled DEM Catchment Areas There are various catchment area tools (eg Catchment Area) which have ...


1

Some recommendations for extracting drainage networks with SAGA. I guess the first thing you do is fill the dem with Wang&Liu. In some cases the result depends on the minimum slope you define. Especially if your relief goes from very high to low and flat areas. The minimum slope is, as its name indicates the minimum slope that you will maintain to ...


1

Not a real answer, but more than a comment.. TauDEM should be able to do what you want, and QGIS provides plugin support for it. There is an existing question here on GIS.SE that you might want to review. [Update/Response to comment] Ultimately your workflow will need to utilize several of the methods to go from a raw DEM to a dataset from which you can ...


1

You could use QGIS 3.0+ / Snap geometries to layer tool.


1

I'm not sure of ways to do that without a DEM, however depending on the size of the project extent I would consider downloading a DEM from the SRTM site and running your analysis on that. The resolution will be approximately 30 meters but its better than not having a DEM


1

I use routinely the grass-qgis extension and its ''hydrological modelling tool'' to create, accumulation and direction raster and river vectors . have a look here: https://www.youtube.com/watch?v=pKn_CMhDMK0 cheers


1

You can use the Raster to Polyline tool to convert your raster containing stream order values as cell/pixel values to lines with that value as an attribute. You can then label the lines using the appropriate field in the resulting attribute table, and either just show the lines over the raster or show only the labels and set the lines to no symbology if you ...


1

The method of classification (Strahler, Leopold and Wolman, Whiting and Bradley, etc) of order that you choose will determine what is considered a tributary, as not all methods will yield the same results. Here is a paper on stream classification in a GIS Here is a jumping off point for you about determining stream order, you may also want to try cross ...


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