Thanks a lot, Dr. Kwast, for these webinars videos. They are very helpful, with lots of tips and easy to follow. I've been learning a lot and I'm very grateful to you.
Thank you for this excellent video. For people like me who have no geographical training the whys of taking steps are very important and you explain it really well.
Hello Hans, Thank you for this tutorial video. I would like to ask you how one can incorporate average sea level rise and RCP 4.5 scenarios into QGIS to model inundation levels
Thank you for this video. Knowing the hydrographic network, how I can determine the longest path from the point representing the section of closure of the basin?
Hello sir, first of all thank you so much for your videos... Sir in my project Stahler order layer is not generating. I have checked all the file and folder names! Can you please help me in this?
Dec 7, 2022. I'm using Ubuntu 22 and qgis 3.22. I notice you use several SAGA MODULES, but I find that I cannot enable SAGA on this Qgis Version. Can it be done?
What if I dont use Strahler Order , but I use Chanel Network and drainage basin instead. because in Chanel Network and drainage basin it also functional option of Strahler Order.
Correct if you don't need the delineated rivers calibrated. But we need to give Strahler threshold number to derive the river with the Channel Network and Drainage Basins tool.
Dear Pr. Hans, I was wondering about the bounding box for the DEM download which shp should we upload in wgs84 or in the desired projected system ? Thank you
It was a very nice and informative video. I have one query regarding spatial resolution since I am using cartosat-DEM having 10 m resolution so can I enter 10X10 while reproject the image.
The higher the value the larger the (tributaries of) the river. However, if you want to find the largest stretch from the source to the outlet, you need other methods.
If you have a CSV file with coordinates, you can use the procedure in this video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-C3AMh3sZzJQ.html. If you want to automatically derive all subcatchments for all junctions in your stream network, you can use this approach: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-5uGaLIlaFh8.html There's also a tool that uses SAGA, which has some issues: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Hqc_1CMadhA.html Finally, there is a tool in the PCRaster Resource Sharing repo that you can use: github.com/jvdkwast/qgisrepository
Thank you for your video. However I have some confusion regarding catchment area delineation, here I noticed that you have used Upslop for delineation up to outlet point rather than pour point In QGIS.
It is the same, but you need to choose or snap your pour point to the delineated stream, otherwise there's no river for the model and it can't delineate the catchment.
Hello Dr. Hans, It is really wonderful to see the webinar. I am facing a difficulty at the stage of correcting the file after reprojecting the DEM using bounding box. I am not able to use the tool "Fill Sinks" by Wang and Liu or any other as each time I open, it says, officially it is not supported. Can you please tell me the reason or any other method to use it.
This message has to do with the new dependencies in the newer versions of QGIS. A work around is in this video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-t-2ExoyhIfA.html
For flood modelling you have to use a hydrologically correct DEM with rivers that match the DEM. That's what you create here. If it's to far off the real rivers you need to burn in the river network. You can try the methods in these videos for example: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-jHT_StPb_oM.html and ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ZyM1jnxFamU.html
Why are some RGB values higher than others, such as 255, which represents a flat area, and others lower, such as 0,1,2,3,4,5,6,7? Are not they flat areas as well? Thanks very much
I assume that you're referring to the Flow Direction map. These are not RGB values, but the values represent flow directions. Each software encodes the compass directions in their own way. Here SAGA encodes it as 0 = N, 1 = NE etc. 255 = flat. Here's an unlisted video that gives more information: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-1gNBdrNMcKk.html
I dont understand about Strahler stream ordering method. I watched other videos after using Fill sink, we calculate flow direction and flow accumulation. Does Strahler stream order already calculate flow direction and accumulation already before it create stream order? How Strahler stream create stream ? thank u
Strahler ordering uses the flow direction. It first gives all pixels order 1, when pixels of order 1 join downstream it becomes order 2, etc. Alternatively you can use flow accumulation with a threshold. Here's the theory ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ZLUjSEK-nbg.html
@@HansvanderKwast Let’s me repeat if my thinking is correct. There are two ways to derive stream : 1). Strahler order;2).Flow accumulation Case A: if I use Strahler order, I don’t need to calculate the flow direction. Because inside Strahler order method it use flow direction already or I can say Strahler order calculate flow direction already before derive stream Case B: if I use flow accumulation, I must calculate flow direction first to derive stream. Otherwise, there is no way to calculate flow accumulation. and if I use flow accumulation, I need to try trial and error… Do u have any documentation/published article mentioned about Strahler order and trial and error of using flow accumulation? May u drop the link ? I need it to support my study. Thanks
Your reasoning is more or less correct. Two methods: Strahler order or flow accumulation. Depending on the tool you need to calculate flow direction before or it's included in the calculation. For both it's used. Also both results need calibration to determine the river. For Strahler it's more discrete, while for for flow accumulation you need to choose an amount. Here's the theory: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ZLUjSEK-nbg.html Please check the videos on the new PCRaster Tools plugin as an alternative for SAGA and GRASS tools.
excellent video, a query how I can generate the catchment point automatically to delimit my basin I see that a coordinate is placed that coordinate how can I automatically generate this for my model
There are several things that you can do automatically. In the step where you do the Fill Sinks (Wang & Liu), you can choose to output the Watershed Basins. That will automatically derive the basins, based on the pits in the DEM. In the tool Channel Network and Drainage Basins that we use in the video to derive the streams, you can also save the basins in raster and vector format. If you choose to save the junctions, you get all outlets of subcatchments. Then you can use the approach in Tutorial 6 on this site: courses.gisopencourseware.org/course/view.php?id=10 You can also automate procedures by creating a graphical model. See tutorial 10 in the link above.
Hi Hans, thank you for the well presented Webinar. This has been very useful for me. I have however, encountered challenges with delineation of catchment section (mins 47 to 49). My catchment raster on a project I am currently working on has the same min and max number (100) and the whole area is black. What could this mean? Does it mean that the whole catchment is draining at the selected outlet point (i.e., the coordinates captured). I also notice that the coordinate capture point needs to be exactly on a stream line to obtain any useful results.
All pixels belonging to the catchment get value 100. So if all your pixels are 100, all drain to the outlet. Indeed the outlet needs to be defined at the delineated stream in order to correspond with the filled DEM.
Thanks for all those webinar, really helpfull ! Am I missing something but I don't have SAGA tools in my QGis 3.12.3. and I can't find it in the repository. Where can I download it ?
If you're using QGIS on Windows you can add it through the OSGeo4W installer. Please note that you're not using an LTR version, which can have bugs. I advise to use the LTR version for learning and operational use. The current LTR is 3.10.6. Newer versions have new features, but can have new bugs too. If you use the stand alone installer SAGA should be included.
@@HansvanderKwast Thanks for your answer ! I'm a Linux user but actually it was a version compabillity problem. I installed Qgis 3.10 and now I can use saga's tools. Btw, I bought yesterday the "Qgis for Hydrological application" and the "Qgis Map Design" book and I'm very pleased with the content. I wish I could have them all ! Again, thanks for your work.
Hello! What would I be doing incorrectly if my streams for Tulare and King County California are coming out segmented instead of long lines. Is it my projection or do i have to reinstall qgis?
Make sure you're calculating the streams from the filled DEM. If that's the case, probably the DEM has issues or the area is too flat. You can try other algorithms, for example from the PCRaster Tools plugin. See this playlist: QGISHydro Chapter 4: Stream & Catchment Delineation: ru-vid.com/group/PLeuKJkIxCDj05rwD3Fun7v7rpVRg7c_kE
Hello, I'm new using QGis, and your videos are very usefull, thanks for sharing! I have a doubt please. When I try to run fill sink I have a warning, it says "files are not supported as outputs for this algorithm" but I have a result, and when I try to generate channels, it doesn´t make it, I have the same error. I'm using Alos Palsar DEM . Would you mind please tell me how to fix this problem?
Hello, First, thank you for all the amazing webinars. They have helped me a lot I am hitting a bump when trying to use the Upslope tool. I am sure the point falls on the 30 x 30 and I chose the filled DEM as the elevation. When I run the tool, I get the error: Tool needs graphical user interface. Thank you in advance,
In newer versions of QGIS they've upgraded SAGA to a version where the Upslope Area tool doesn't work anymore. The problem is described here: github.com/qgis/QGIS/issues/44514 and in this video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-9fWQZqPjPVk.html There are 2 work arounds and 1 better alternative that I'm using now. Work arounds: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-t-2ExoyhIfA.html ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-B1LMOOPMWgo.html Alternative, more robust, tools via the PCRaster Tools plugin: Installation: jvdkwast.github.io/qgis-processing-pcraster/ Catchment delineation: ru-vid.com/group/PLeuKJkIxCDj05rwD3Fun7v7rpVRg7c_kE
Hi. It doesn't need flow accumulation. The method follows the flow direction and adds up the orders starting with giving all pixels order 1. When they join of same order, the order increases downstream. See: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-SuFl8EWDqfU.html
@@HansvanderKwast probably it is just because i am used to diffrent workflow , generally i like that qgis can do all of this ,thank you sir for everything
@@rami7012 Thanks. You can also use the flow accumulation workflow in QGIS. Here's a video with in the end a comparison: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-aTYHpft1gus.html
I'm currently using QGIS 3.18, and as I go through the clipping extent, I notice that there is no select extent on canvas for the clipping extent, as I only have calculate from layer, use map canvas extent, and draw on canvas. How should I proceed with clipping extend before using the crayfish plugin? I was also wondering whether if I could skip the clippping extent and just go proceed for the crayfish plugin? Thanks very much
In QGIS 3.18 you can still clip by drawing the extent on the canvas: Raster -> Extraction -> Clip Raster by Extent. There at Clipping Extent use the drop down on the right to choose Draw on Canvas. Clipping might not be necessary. In my case the file was too big to load, so I had to make it smaller. There are also other ways to clip. You can clip to a polygon mask for example or use the canvas extent when you're zoomed in to the area you want to clip.
I actually have added a DEM and clipped it earlier following the district shapefile area at the beginning of the layer. But I don't know why as I draw on canvas to clip the raster and proceeded for crayfish, the flow direction only within the box that I draw and not outside the box. I wonder whether the file is still too big to load? I actually was hoping to see the arrow of flow directions will be inside and outside of the box. What should I do? Thanks very much
@@HansvanderKwast I was able to generate the catchment polygon based on my district area shapefile using QGIS 3.18.3. How do I proceed from the catchment polygon if I want to generate data for multiple sub-catchments for the other surrounding villages that are not within the generated catchment polygon? Thanks very much
The bounding box is something you create based on your expert knowledge by looking at the relief and rivers in the area of interest. A nice way is to zoom in to the level that the map canvas covers your study area. Then use from the Processing Toolbox: Vector Geometry | Create layer from extent. Then choose Select canvas extent. More info about the need of clipping to a bounding box in this video: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ZLUjSEK-nbg.html
Fill Sinks (wang&liu) after run :"You can check the 'Log Messages Panel' in QGIS main window to find more information about the execution of the algorithm"
It seems you're writing the result to a VRT file. That doesn't work apparently. Instead of a virtual file you should use a raster format like GeoTIFF for the output.
It's a Processig Provider, so you need to install PCRaster as well as the plugin. Instructions in the documentation: jvdkwast.github.io/qgis-processing-pcraster/
The DEM that is used is SRTM. You can download it from USGS Earth Explorer (earthexplorer.usgs.gov/) or use the SRTM Downloader plugin. The bounding box was created by zooming to an area of interest and use the Create layer from extent tool from the Processing Toolbox.
25:23 I think it did not work because it was set to "user defined", at least when I do it, the extent option gets greyed out. So the way It worked for me was Min/Max Value setting to Min / max and statistics extent to Updated canvas.
Thx for the presentation. I tried to do the same with Dutch AHN3 data (resolution 5 x 5 m), but the problem is that many streams passed roads via culverts. By using the Strahler order the streams will stop at the roads. Why didn't you have that issue with your data? Is that because of the raster width of the elevation data?
Hi Barend. There are a few considerations here. The DEM needs to be "fit for purpose". First, it is not always true that a higher spatial resolution will always give better results. On the contrary, I would say. If you're delineating large streams and catchments, a coarser DEM, such as SRTM 1 Arc Second is often sufficient. Second, you need a DTM instead of a DSM. The AHN3 is available as both. In the DSM you have your surface objects, while for stream and catchment delineation these need to be removed to have the elevation of the terrain. Now, the coarser your DEM, the more close it gets to a DTM. Here's a video about DEM's: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-pnAdasqHxGk.html Here's a video about the theory of stream and catchment delineation: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ZLUjSEK-nbg.html
