Snap pour points and delineate multiple catchments in QGIS

This video shows how to snap pour points and delineate iteratively the catchments of those points.
A lot of ArcGIS users had requested this feature. During the QGIS hackfest in A Coruña I developed a tool for this with the help of Lutra Consulting.
The processing tool is not in the official QGIS plugins repository, but you can find it here: github.com/jvdkwast/PyQGIS_Hydro
This video is part of IHE Delft OpenCourseWare. For more free GIS materials check www.gisopencourseware.org
(c) OpenStreetMap Contributors
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Note that with the new dependencies in QGIS this will not work.
For work around see: • Install QGIS with SAGA...
And also see: github.com/qgis/QGIS/issues/4...
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[@tzevoon]

Thanks Hans for another great video. This is indeed very useful.

[@tranngochuan9068]

Dear Hans, Thanks for your sharing. It is a fantastic tool. I love Holand

[@max7164]

Hi Hans, I was wondering if there might be a way of using this tool to produce a set of non overlapping catchments for use in a hydraulic model (ie to avoid double counting runoff surfaces)? What would you suggest to avoid overlap or to remove after?

[@HansvanderKwast]

I often get this question. The subcatchment of a downstream outlet always includes the subcatchment of the upstream outlet. In other words, all water from an upstream outlet also enters the downstream outlet. If you don't want subcatchments to overlap, you need to choose outlets that are not part of the same larger (sub)catchment. Not sure how hydraulic modelers deal with this.

[@max7164]

@@HansvanderKwast Thanks for you answer. This ends up not being the case, however, in urban settings due to flows "leaving" the overland system to go into the underground drainage system. I think the answer lies in somehow subtracting upstream catchments from larger downstream catchments like this, bit.ly/3iWqVef. I haven't yet found how do this on a large scale for hundreds of drainage gully catchments though... I feel like this is critical for more accurate flood modelling in urban environments.

[@max7164]

I Think I've cracked it! Fill DEM sinks > Delineate channels > Snap drainage gully points to channels > rasterize gullies and burn into DEM > run your iterative script using snapped gully points and burned dem > merge catchments. This ensures that flow accumulation "stops" at each gully point. In the future I can imagine also correcting the initial filled dem by raising buildings and burning roads. The aacuracy of the process is increased by using a fine dem (I used 0.5m resolution) as the dem will represent road grading towards curbs and delineated channels will pass closer to gullies. But probably not a must as I can imagine this would take a very long time to run for larger catchments.

[@max7164]

I think the only remaining point is to amend you script in order to assign the gully reference to the newly created catchments in order to assign them properly within the modelling software. Thanks again for your channel, it's been very helpful!

[@MrLikeidontcare]

@@max7164 How did you burn points on to dem?

[@abhimanyukumarbarnwal4616]

Hello Hans, I have a question, is it possible to have a rainfall runoff model in a given catchment. Like if total rainfall in five rainfall station in 3 days is average 40 mm per day per station, then the increase in discharge would be how much.

[@HansvanderKwast]

Yes, but then QGIS is not the tool for this. You can use existing models, such as SWAT or you can develop a rainfall runoff model with PCRaster. At IHE Delft we offer courses on modelling. Have a look at these: www.un-ihe.org/short-courses

[@JP-sc7ye]

Hi, is there an easy way to relate the point shp to the catchment? I was thinking in just do a intersect but that wont work because some of my basins are overlapping. I appreciate any comment on this

[@HansvanderKwast]

In the latest version (not covered in this video) you can choose the field from the point file to use as a catchment ID. See readme here: github.com/jvdkwast/PyQGIS_Hydro

[@poetrybypranshubhardwaj7753]

Hii , useful video as I have switched from arcgis to qgis recently. I have this file extracted in the correct path but in plugins I can't see any point to catchment option. What could be the options?

[@HansvanderKwast]

If you're using 3.14 it's not working. 3.10 should work.

[@poetrybypranshubhardwaj7753]

@@HansvanderKwast oh thanks

[@acapsaintjohn893]

FYI, I tried downloading this and following what you said and when loading into Qgis it says the plugin in broken because it is missing a metadata file. I put the files in the appropriate python/plugin folder and extracted them there. I loaded up using plugin toolbox and uploading from zipfile

[@HansvanderKwast]

You can file an issue in the GitHub repository and mention the QGIS version, operating system, screenshot of error and any other relevant info.

[@Truthcube]

I had the same issue. The "points_to_catchments" directory must stand in the ./python/plugins directory, not the whole archive "PyQGIS_Hydro-master"

[@nischalkarki2960]

What is different in this tool than pcraster subcatchment?

[@gemmam9892]

Hi Hans! I want to delineate the catchments of multiple sites along a river. I have tried your video instructions to snap sites to the river channel, but the 'Snap Geometries to Layer' tool produces the following error: Feature (12) from “channels” has invalid geometry. Please fix the geometry or change the “Invalid features filtering” option for this input or globally in Processing settings. Do you have any suggestions?

[@HansvanderKwast]

Run "Fix geometries" from the Processing Toolbox.

[@ninar3674]

Thanks for the video. Unfortunately my watersheds are single pixels. What am I doing wrong?

[@HansvanderKwast]

Check if you're using a filled DEM. If that's not the problem check the projection of the DEM. It should not be in a Geographic Coordinate System with lat/lon coordinates.

[@alexander_rebelo]

@@HansvanderKwast I'm having the same issue, points on flat filled depressions are single pixels and other watersheds are small elongate shapes that do not fill the entire watershed. Perhaps it would be worthwhile sharing some standardised input files so we can better troubleshoot these issues? Thanks

[@timhowson3445]

Me too. I'm using OSGB36 projected coordinate system.

[@camilaabea]

Have any of you figured out the problem and as successful in creating your catchments? I have the same problem and I'm using a filled DEM in UTM projection

[@user-gm3zp2yf3n]

Hello sir, I am a beginner in QGIS. Learning from your elaborated videos. I am not getting the part where you are taking pourpoints layer. Can you please elaborate?

[@HansvanderKwast]

Pour points are the locations for which you want to derive the contributing areas (catchments).

[@lucataddei9305]

Hello and thanks for the plugin (it would be very very useful to me) and the channel! I have a question: i have repeated all the steps with QGis 3.10 and the plugin apparently runs (same messages as in the video) but in the output folder i don't find any shapefile. With QGis 3.4 in gives me an error (_core.QgsProcessingException: Unable to execute algorithm Could not load source layer for INPUT: TEMPORARY_OUTPUT not found). What could be my problem??? Thanks for your time! Luca

[@lucataddei9305]

I add an extra information: to obtain the layer "channel" i used the plugin "channel network and drainage basins". The other steps are the same to this video. Thanks again

[@HansvanderKwast]

Hi Luca. Good to read that you're trying the plugin. It's a bit experimental. Not sure what the problem is. It might not be very robust yet. Do you have spaces or exotic characters in the path (folder names)?

[@lucataddei9305]

@@HansvanderKwast I've tried to change the folder and put every file on desktop but nothing. The same if i use points without the "snap step" so i think it could not recognise the movement to the channel. I'e tried to use the "unslope area" command and it works. I'm not yet an expert QGis user and i could have made a stupid mistake without knowing. Last question: it is the first time a install an external plugin: if i see the plugin and i can use it means that the passage is correct, right? The problem should not be in the positioning of the folder i think... Thanks again and i will continue to try!

[@HansvanderKwast]

@@lucataddei9305 Indeed if you can see the plugin then the installation should be okay. Not sure what the problem is. Desktop is not a good idea because often the path causes problems. If the Upslope area tool works, it should work also in the plugin. Did you check if the projection of your points vector is the same as the filled DEM?

[@lucataddei9305]

@@HansvanderKwast Yes, both in EPSG 3003. It is a very strange thing! tomorrow i will keep trying

[@anagabrielacruzbaltuano4157]

Hi. It isn't working with QGIS 3.16.. Any idea of how I can solve that issue? Thank you in advance.

[@felixconitz2950]

in 3.14 it works, check out my comment ;)

[@xhuljosema9800]

Hello Hans. I am a begginer in QGIS. Regarding the video, i have a question. I installed the plugin succesfully. My aim is to create a catchment with different subcatchements like in your video. I tried to put some pourpoints by creating a new shapefile. After that, I run the plugin *calculate catchments from points* but it shows me an error (Algorithm saga : upslope area not found). I tried to use the upslope area from saga and its works but only for one point. Please can you help me to solve the problem?

[@HansvanderKwast]

You probably need to modify the script. I discourage using this tool, due to challenges with SAGA. It's better to use my workflows with the PCRaster Tools plugin. Check the videos about that on my channel.

[@xhuljosema9800]

@@HansvanderKwast Thank you. Regarding the challenges with saga, you are saying that saga maybe is blocking the tool works or is something else? I will try to use PCraster plugin also

[@HansvanderKwast]

Yes. The tool uses the SAGA Upslope Area tool, which now expects a SAGA user interface instead of QGIS. There are work around videos on my channel, but PCRaster is a great reliable alternative.

[@xhuljosema9800]

@@HansvanderKwast Thank you

[@user-te1td2hb9j]

Great video and plugin! Note that for QGIS 3 you need a workaround, shown at kzbin.info/www/bejne/ql6Vdqulrs18nKM. Otherwise the plugin doesnt work.

[@joeparescario7823]

Sir Hans what is wrong with this it says like this...Unable to execute algorithm Could not load source layer for INPUT: C:/Users/hee/AppData/Local/Temp/processing_HgBygo/8109ae3e18954a07bca4ff0a8652b044/AREA.sdat not found

[@HansvanderKwast]

This tool relies on the SAGA Upslope area tool which doesn't work anymore in newer versions of QGIS. I strongly recommend to use the new PCRaster Tools plugin instead. If not, check the work around videos on my channel.

[@gemmam9892]

@@HansvanderKwast Hi! I am getting the same error message. What PCRaster Tool are you referring to? Do you have a video on this? Thanks!

[@HansvanderKwast]

@@gemmam9892 There are 2 work around videos for SAGA to deal with this error: kzbin.info/www/bejne/ql6Vdqulrs18nKM or kzbin.info/www/bejne/eGKvfoKFhbKKndE Because of lack of robustness of SAGA in QGIS I have switched to my PCRaster Tools plugin. The workflow is the same as here: kzbin.info/www/bejne/eWSkfptpqL-tgLM, but you enter in the CSV file a list of coordinates for the outlets that you want to delineate. You need to do the snapping before. There are tools and graphical models available through the resource sharing repository: github.com/jvdkwast/qgisrepository. Install the QGIS resource sharing plugin. Check here how to add this: kzbin.info/www/bejne/qGbZmYOumqlgo9E