Stream and catchment delineation in QGIS 3
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- Опубліковано 2 сер 2024
- Stream and catchment delineation in QGIS 3 using only Open Data (SRTM).
This video is part of IHE Delft OpenCourseWare. More free resources can be found at www.gisopencourseware.org
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More information about the book "QGIS for Hydrological Applications - Recipes for Catchment Hydrology and Water Management" by Kurt Menke and Hans van der Kwast can be found at the website of Locate Press: www.locatepress.com/hyd
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Credits for OpenStreetMap data: © OpenStreetMap contributors
SRTM data can be downloaded from: earthexplorer.usgs.gov
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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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#QGIShydro #QGIS #IHEDelft
I watched this tutorial during my final year at varsity in 2019 for a design project we had. 5 years later and I return to this tutorial for a big project in Africa. Hans, thanks for this brilliant and elaborate video, appreciate it dearly.
This is one of the best tutorial videos about QGIS I have ever seen. Thank you for your effort.
Excellent lecture and well organised covering major comands of qgis 3 with detailed explanation and demonstration simultaneously.
You're a teacher by "blood", really excellent content...tried the tutorial on my own maps an areas, and it is amazing how easy this can be done just following your step wise tutorial. Greetings from Norway, and a thousand thanks!
Super helpful video. Just starting out my GIS journey. This will save me heaps of time trying to manually delineate catchments and produce maps! Thank you!
Amazing tutorial, I am learning a lot from your expertise. took me a few hours to do it but finally completed all. Now I will apply this to a different catchment.
Literally just mind blowing
Hi Hans, everyone seems to have doubts and we are used to be in a kind of a rush, but I just wanted to let you know that we deeply appreciate the work that you have been doing. This video was exceptional; the language you used was concise, clear and it worked flawlessly for me. Thank you so much!
Thanks Bruno!
Thank you so much for uploading so many useful videos, I've been trying to generate catchments for a long time and this is the first time I've managed to get it to work! Thanks again!
Nice to read that! Thanks!
Really good lesson Hans. Clear and easy to follow.
Thanks for the in-depth and detailed walkthrough.!
I found this video very informative, I am a new graduate and this has helped me greatly in my new job
Why couldn't I have found this at the start of my project! Great presentation, I'm now going to go and watch the rest of your content.
Thank you for this excellent tutorial.
Thank you very much! Before I did it with hydrology package in Arcmap. Fantastic!
Thank you Hans very helpful for my projects in Vanuatu
Thankyou so much for your detailed explanation
Best tutorial on this topic, thank you very much
Thank You for your explanation, it's very useful
Thanks Hans, very helpful.
Thank you for this. Very informative.
Thank you! Nice explanation.
Hi Hans,thankyou for this tutorial.
Amazing video, thanks for share
This is awesome! Thanks!
Thank you for the tutorial. I have managed to generate a catchment of my own
Thank you so much!
Thank you :) Very informative
Thank you so much! It was the best video for qgis ever for me. =b
thank you! best ever
thank you
Thanks for sharing!
Thank you verymuch
*Great Tutorial 👍👍👍*
Thank you so much. Very help me
Nice one. Thanks.
that's a good tutorial ,thank you
Thanks sir
Thanks a lot for this very informative video.
In the processing toolbox you can find a tool called Fix Layer Geometry. If you use this first, it should work. Alternatively, you can calculate a buffer of 0 of the catchment polygon, that also repairs the polygon.
@@HansvanderKwast thanks a lot.
Fill sinks 10:30
Creating Stream Order - (Strahler order) 15:40
It took me a while to grasp because I'm a beginner, but the video was very helpful.
Very good demonstration sir please next video uploaded the Stream order calculated and show on River map in QGIS
Is it possible to delineate only right or left hand tributaries of one river separately?
Hi Hans. Great video, again! I was wondering how you would go about doing this in a heavily urbanised catchment in order to generate "sewer catchments"? I have access to very detailed 1m resolution DSM. The idea is to use this to create our urban "sub-catchments" for use in a hydraulic modelling software. My first idea is to burn the drainage network into the DSM. Would I burn the pipes only or nodes as well (manholes/gullies) in order to create local sinks? Any ideas/ advice would be great. I appreciate you're likely a busy guy. Thanks!
Hello Hans, I've found this tutorial very helpful. As a beginner for QGIS, I am having difficulty to calculate the maximum flow path and average slope of the catchment I have. I was able to generate a raster "Flow path length" map using "Flow path length" tool in SAGA, but I do not know how to convert that into a vector stream line from which I can read the maximum flow path, and its average slope. If it is worth to be your next tutorial.
Best
Is it possible to delineated a catchment from a particular point on a map? I need to assess a road culvert and wonder if I can get a catchment upstream of the culvert.
the principle is the same, just follow the video and pick your point of interest at the culvert inlet
thank you for your tutorial that you put online it is really for us I will ask myself I am a student djama brice in Master 2 at the university Félix houphouet boigny of Cocody side of Ivory. I have a problem to make the pollution vulnerability map on the Qgis 3.16 software. can you help me by making a tutorial on calculating the vulnerability index under qgis 3.16.
Can the drainage channels be considered as stream network?
Thanks for your videos, they are great. I have a problem with small catchments though, even if I pick a point that falls onto the stream DEM, the up-slope area algorithm gives me a completelly black DEM, how could I solve that and get the area for a whatever sub-catchment?
Hi Angelo. Thanks for using my videos. Maybe you can send me some screenshots so I can check your problem?
Hi Hans,
I managed to solve the problem I think. The up-slope output is sometimes a black DEM but as you suggested, by adding "0" to "Additional no data value" in Properties/Transparency, the DEM shows the watershed delineation, I just do not understand why it happens only in some case. Any clues?
Thanks
Hello, I'm new to GIS and this is a fantastic video, thank you! I am examining the catchment of a lake in central America and I have an issue which the method you outline doesn't handle quite so well. That is, there is an area of extremely flat topography with a major river that I suspect will change the drainage characteristics of the region, bu due to the topography the calculated Channel Network Algorithm separates to sections of the river, irrespective of Strahler Order selected. Is there a workaround for situations like this? Any help or guidance would be greatly appreciated and I can provide further detail if you require! Thanks, Matt
I see that there is a video on "burning in rivers". Sorry I was unaware of this terminology. I will explore these options!
Sir, kindly tell the steps to find out the "Longest Flow Path" in that Catchment Area.
Hi Hans! Great video. Im perhaps stuck at a very basic step. At 23:31 when you use the directional legend for your colour ramp for the flow direction raster, how did you do that? Where can I find that legend?
Hi Ruchi. Please checkt this video where that's explained clearer: ua-cam.com/video/2Ub0c7Ss-T4/v-deo.html
Hi Hans... How do you extract the main river flow path... and its extension?
The Strahler order method was used to delineate the river and its tributaries. ua-cam.com/video/SuFl8EWDqfU/v-deo.html
Best lecture so far. How do you proceed calculating the area of a catchment?
attribute table, geometry, area
EXCELLENT video, I ALSO PURCHASED THE BOOK, FANTASTIC!
TO VIEW THE SUBBASIN?
I'm having problems with the fill sink part. The running of algorithm always fails. what should I do?
What a coincidence! I was facing the same problem. It was happening because of saga. You have to manually install saga gis and add it to qgis toolbox.
Thank you so much for this tutorial.
I have one issue though . When trying to re-project the mosaic to my project CRS (GDA94 EPSG : 4283) It gives me an error. Is there a way I can get around this ?
Cheers
You are using a GCS with degrees as units. You need to project the data to a metric coordinate system.
Hello Sir, at 23:24 how did you customize the bands?
This video would help you ua-cam.com/video/q54xTyV7gAE/v-deo.html
Is it possible to delineate sub catchment? Thanks so much for your wonderful QGIS tutorials
Yes, in the same way. Or if you have multiple outlets you can do it automatically. Check the other videos on my channel.
worked great! is there any way to make improve accuracy of rivers in lowland areas where there is little elevation difference? thanks!!
You can play with the following:
1. Use a smaller minimum slope value in the fill sinks algorithm
2. Use another algorithm than D8, try MFD or D-INF
3. Burn in the river system so the water is forced to follow more realistic water courses. Some videos on this channel about that.
@@HansvanderKwast okay great, thank you!
how to participate in your QGIS course?
Sir how to create basin shape file and download Landsat path/row tiles for the same sir ?
Thank you sir hope here from you soon sir
Thanks for the great video.
Question: In attribute table, is the number '100' the catchment area (= area of the polygon?). Otherwise, how can we calculate the catchment area finally of the Rur_catchment polygon?
You can calculate the area of polygons with the field calculator. Use the $area function.
@@HansvanderKwast whats the unit of area calculated?
Hi Hans, this video is really useful. Thank you for making it. How to make sub-catchment areas? You have made drainage basins for different rivers including Rur river but my question is how to create the sub-catchments inside the catchment of Rur river? I will really appreciate your help. Thank you!
Check the new tutorial on this page: ocw.un-ihe.org/course/view.php?id=11§ion=10
@@HansvanderKwast Thank you very much, Hans! I got what I was searching for.
Hi Hans, thanks for the good explenation! Please how to Delineating Multiple catchment with QGIS.
You can use the Points2Cathchment plugin from my GitHub page: github.com/jvdkwast/PyQGIS_Hydro
Great tutorial, thanks. I'm not understanding how to obtain the cardinal directions for the flow direction legend. The stack exchange discussion doesn't seem to explain it clearly. I get the d8 model and that the it corresponds to the direction gradient of each pixel, but how do you set it? I have 0 and 255 as values once I complete my flow direction... do you have a clear guide as to how to assign the cardinal directions?
Hi Olivia. Are you referring to this discussion: gis.stackexchange.com/questions/254939/legend-of-flow-direction-calculated-with-processing-toolbox-qgis-saga ? In my video we use SAGA tools, so 0 is North, 1 is NW, 2 is W, 3 is SW, 4 is S, 5 is SE, 6 is E and 7 is NE. 255 is for pixels without a flow direction (flat). Hope this helps.
Hello sir i have same issue too. I have values ranging from 0 to 255 in the flow direction map. How can i convert this ti have the direvtion N, NW etc?
See the answer above. Or check gis.stackexchange.com/questions/254939/legend-of-flow-direction-calculated-with-processing-toolbox-qgis-saga
What is the year of the SRTM DEMs, I am trying to find the year that these were generated and can't find it. thanks
Acquisition date of SRTM is 2000.
@@HansvanderKwast thanks
Thank you, Professor, it really helpful. I have a problem regarding the extraction clip raster by mask layer. I am not able to save the clipped mask into .sdat format. I have chosen Float32 as the output data type. Fyi, I am using QGIS Madeira. Do you have any idea?
Maybe you got a "geometry error"? In that case you can use "fix geometry" from the processing toolbox.
@@HansvanderKwast Thank you for your kind reply. I will do it.
Hi Ferdinan, please I'm having a similar problem. Did you get the solution? I try the procedure that the Professor suggested but it didn't fix the problem
Hi Hans, when I run "strahler order", streams in my image look incomplete, there are gaps between streams, main rivers are absent. Even when I do calculations and get rid off minor streams, still few streams are left, which are not connected with others and look isolated....
There might be problems with your filled DEM. Maybe you have voids?
Dear Hans, thanks for the very usefull video. I have a problem with the Uplslope area function. The system creates the catchment area that I select but the max. and min. values are changing between 100 and 100. In your case it was between 0 and 100. Therefore, my vector file does not seperate the selected catchment area from the complete rest DEM file. I tried to change also the max. and min. values by setting up the min. as 0. However nothing is changing. Do you have any opinion regarding the reason of the problem? Thanks in advance.
Sir, Can i get DEM from SRTM of less then 30 m pixel resolution…. ??? Actually my river channel are very small and 30 m pixel almost covers entire width of the river…
Hi, what value i should put while creating filled_DEM for 1.5M drone resolution? DEM, Not able to generate the strahaler order DEM.
Make sure you have filled the DEM before calculating Strahler orders. You can use SAGA Fill Sinks Wang & Liu from the Processing Toolbox.
@@HansvanderKwast what value should i put in dem_filled in place of resolution? My dem is 1.5 m resolution
Excellent explanation!
I've seen in QGIS 3.10 that the value of area of a given vetorial layer can vary a lot depending on both the Coordinate Reference System (CRS) of the layer and the CRS used to proceed with the calculations. Since I'm in Brazil, I usually work with SIRGAS 2000, UTM zone 22S.
An example of how different the values can be: I've drawn a square with a 10 km side (using SIRGAS 2000, UTM 22S). The calculated area with WGS 84 gave me 41 km² instead of 100 km². The same great difference happened when I did draw the very same square using WGS 84.
My question is: what's the rule to calculate the area in order to get a real value of the portion of land I'm working on?
When I used the "None/Planimetic" option to obtain the area (layer with SIRGAS 2000), I've got the right value. But I want to consider the surface curvature.
Thanks. First, never use a GCS (Lat/Lon coordinates) for distance and area measurements. Second, choose a projection that doesn't distort surfaces. See: ua-cam.com/video/jVn1uCuhO_4/v-deo.html
This is great content and an even better explanation! I just have one question regarding the fill tool. My computer can not execute this function what can possibly be the problem? Is it the RAM or maybe something else?
RAM can be the problem indeed. Check if you can use a coarser spatial resolution for your study area. < 5 m will not improve the results and for large catchments 30 or 90 m is okay too. I recommend at least 16 GB of RAM. If the size is not the problem, check if you use spaces and strange characters in file/folder names and if there are no voids in the raster. Also if the area is too flat you'll run into challenges.
Thank you for the detailed answer. I appreciate it
Hi. I wanna know what is an .adf extension for? And how can I have that file cause I need it for SWAT+. Thank you.
It's the ArcInfo Binary GRID format. gdal.orgdrivers/raster/arcinfo_grid_format.html. Unfortunately it is a proprietary format. It can be read by gdal, but not written. Not sure about SWAT requirements, I'm not a SWAT user. Check QSWAT for use with QGIS.
I have several questions about this video:
1. I can't use Upslope Area because my project wasn't generating in a proper way. What should I do? Should I start from the beginning?
2. What version of QGIS 3 that you use? Is there any big difference between your version and the newer one (I use QGIS 3.16 Hannover version)?
Thanks
1. Make sure you're using your filled DEM and you're choosing the coordinate in the delineated channel (zoom in).
2. Only little differences with newer versions (such as click right to copy coordinate).
Also watch other videos on this topic. There's a playlist: ua-cam.com/play/PLeuKJkIxCDj2Gk0CkcJ-QeviE41aMZd-5.html
Many thanks for your awesome tutorial Hans. I'm receiving the following error when I want to build a virtual raster. What's the problem? and what should I do?
Loading resulting layers
The following layers were not correctly generated./Users/parsa/Desktop/QGIS/Rur/DEM_Mosaic.vrtYou can check the 'Log Messages Panel' in QGIS main window to find more information about the execution of the algorithm.
Thanks. I can see you're saving files in your desktop folder. It's recommended to save it in a dedicated folder on your hard drive so the paths don't cause problems. Not sure, but it might be the problem here. Also check this video on good practice: ua-cam.com/video/kggwFZHXCl4/v-deo.html
@@HansvanderKwast Dear Hans, Many thanks for your reply. I tried that but didn't work. I tried the QGIS on my Windows (the problem was with my Mac) and all worked well.
Hi Hans, I played the dem with your guidance but found that my river value is always the small ones. Why will this happen?
I can only think of 2 reasons:
1. You didn't use the filled DEM for calculation of the Strahler order. Then it never gets into the higher orders.
2. You're applying it to another study area where there are a lot of small rivers?
Sir I have a problem while working on channel network and drainage basins part. My layers are not generating.
Any idea how to overcome this.
There might be many reasons. First you can try changing the directory. If it doesn't work you can generate the filled DEM again and try
Hi Hans such an interesting and helpful video.....may I ask where I can download SAGA for free as I cloud not found it like the other plug in?
The SAGA tools should come with your QGIS installation and you can find them in the Processing Toolbox. If not, you can try to create a new profile or reïnstall QGIS. In the Windows LTR version it should be present.
@@HansvanderKwast already figure it out thank you!
Hi Hans, thanks so much for your videos, I have used them a lot while studying limnology at BOKU. I'm having an issue at the thinning step - too many cells are removed and the line is no longer continuous, which leads r.to.vect to create many small lines. Any suggestions?
Hi! Probably something went wrong before. The question seems to be at the wrong video, because this video uses SAGA, which doesn't need r.to.vect. I assume you're using the PCRaster approach in this playlist: ua-cam.com/play/PLeuKJkIxCDj05rwD3Fun7v7rpVRg7c_kE.html&si=kd661MjchSynsclX. Please make sure you follow all steps carefully. Check if the raster streams were still connected before thinning. Also check if your projection is correct (should not be in Geographic Coordinate System) and make sure you use the correct inputs all the time. For further questions about this approach, please post the question under the appropriate video.
This means that you can't automate this approach on Mac, unless you find a way to build PCRaster from source code and use it in your regular installation. Unfortunaltely, I'm not a Mac user, so I can't help you with this.
Hi Hans. I am confused on why in newer tutorials you use PCRaster plugins and in this one you did the same analysis with out PCRaster. Is that because with PCRaster you can edit the stralher order? Regards
It's because there are issues with SAGA in newer QGIS versions. Check also this webinar ua-cam.com/video/M9hmN-szO4k/v-deo.html at 10min53s
@@HansvanderKwast thanks.
Hello there, thanks for the explanation. I have a problem with my QGIS 3.10.9. When I made the virtual raster, it won't show when I delete the tiles from the previous step. Can I get your help?
Are you sure that your layers virtual layer was on top of the other layers? If it's below you can only see it by switching off or removing the other layers.
@@HansvanderKwast When I unticked the other layers except for the virtual raster, nothing shows up.
@@HansvanderKwast Never mind, just fixed it.
Having terrible trouble making the Upslope algorithm work at all. I'm getting nothing - what am I doing wrong?
Can you send me an e-mail with screenshots so I can have a look?
Hi.. I see your this video.. and i see the drainage basin and catchment boundary which you derive is same , then why you create again catchment by upslope area tool, while it was also done by drainage basin? also i want to know weather drainage basin and catchment may differ or not?
They are not exactly the same. The drainage basins derived by the channel network and drainage basins tool derive all basins in the DEM based on the flow direction. The upslope area tool will delineate a specific catchment that belongs to a specific point in the river that you indicate in the tool. That can be the outlet or any point in the river. It calculates the area that contributes to water flow at that point.
@@HansvanderKwast Thanks for giving me clarity on this.
Thanks for the video, as a beginner it is very helpful but i faced a problem while generating the Strahler order for the area of interest, it shows a error saying "The following layers were not correctly generated" and gives information about the location of the save file. im currently using qgis version 3.10 , please help me out with the problem
Make sure you've upgraded to 3.10.3 and you don't have spaces in file and folder names. Also check if you've used the filled dem and it doesn't have voids.
Hi there. Hans. I have a shape file of river lines. But with the automatic digitization of the raster, the directions were lost. Please tell me how to automatically set the directions of the lines in the correct direction according to the DEM. (I work in QGIS 3.14). Thank you.
Hi. When you derive the channels using the method in the video, the flow direction of the lines should be correct. You can only reverse the flow direction with a tool from the Processing Toolbox --> Vector Geometry --> Reverse line direction.
@@HansvanderKwast I asked about a special case. My digitization was based on cadastral drawings of rivers, not on your algorithm.. Therefore, many directions of the lines are broken. I need to select and turn in another direction the lines of rivers that "flow up". Altitude is present. Thanks.
Unfortunately, I don't know another way then manually choosing the segments and use the reverse direction tool.
Often I encounter an error when I try the "fill sinks" function. I am following every step of yours and it works on some catchments but doesn't on some others. What could be the problem? Is it important the "output layer type", because it's Float32 by default in your video and different in my project, so I always change it to Float32 as well?
Fills sinks gives problems in the following cases:
1. DEM too flat
2. DEM too large for memory
3. Geographic Coordinate System used instead of projection.
4. Spaces in folder and file names
@@HansvanderKwast Thank you so much, sir! The problem was with my folder's name, which contained a special character. Now it works perfectly. Please keep posting these amazing tutorials, they mean so much to me and many others!
Thank you very much for this video. my network is timed out so I can not zoom into map....could you please help me with problem?
I assume you're referring to problems with access to online layers from the QuickMapServices plugin. I can't solve that if your internet connection isn't good enough. Then you have to find some offline reference maps.
I am trying to use the strahler order on the Jhelum River, India but its not working there!
What should I do ?
Check other answers to comments here and related videos in the catchment delineation playlist on my channel.
Hi, Hans Great video. I just struggle when creating a catchment with SAGA upslope area. It does not create a file, and there is an error in the log file. "Error: Coordinates of target point outside of DEM!
Error: executing tool [Upslope Area] " I used the coordinates as given in the coordinate capture. What am I to do?
Hi. That's probably a mismatch between your project projection (on-the-fly reprojection) and the projection of your filled DEM layer. The coordinate capture tool uses the project projection. Here's an explanation: ua-cam.com/video/vOEGsFFCz18/v-deo.html
Thanks, Hans, you were spot on.
Can WARP (Reproject) be done for less than 30m like 5m or 10m
Yes, but it doesn't make sense if your input is of coarser resolution. You'll not really increase the spatial resolution, but just cut the pixel in pieces with the same values.
Hi Hans. thanks for nice and useful video. i successfully delineate a small watershed. i then tried to delineate a big watershed. it need 30 DEM tiles. till fill sinks it was okay, but my laptop got hang at the time of fill sinks. i tried several times. same result. suppose you want to delineate the whole river basin area of Amazon, how will you do that? same process or have some tips?
First your DEM needs to be "fit for purpose". If you want to delineate the entire Amazon basin, it's not useful to use a high resolution DEM. The pixel size can be even larger than 1 km. Then you need to look at high performance computing if you still don't have enough computing power.
@@HansvanderKwast Thanks a lot.
hello, thanks for the video it really helps me in class. but, i have problem regarding Strahler order, it seems that there's no "lines" corresponding to the actual river in the map, upon closer look there's pattern to identify the river but no actual thick lines, is there anything i can do ? i use both DEM from NASA and government, but the result still the same. thank you for your attention
Hello Kevin. Please check this more elaborate video: ua-cam.com/video/2Ub0c7Ss-T4/v-deo.html
Also check this video for the styling of the rivers, which might be a reason that you don't see the result: ua-cam.com/video/VnmZob59TPc/v-deo.html
I hope it provides the answer. Otherwise let me know.
Please note that the derived rivers will not follow exactly the real rivers, because it's a model based on your DEM and gravity. Human interference and flat areas can give issues.
I have the same problem, my main river seems to be 'missing'. Have you found out what is wrong?
@@HansvanderKwast thank you, apparently using GRASS tool has help tremendously
@@zeldaspijkerman5029 you could check his tutorial using GRASS tool
@@Kevin-fj5oe Thank you, I'll give that a try.
Instead of calculating the catchment area from the Fill dem raster layer, why don't you export the polygon from the Drainage Basins vector layer created before?
Excelent video, thank you very much for the explanation
Thanks. The automatically calculated drainage is not the same as the one from a specific outlet chosen by the user. Often you want the catchment belonging to a specific outlet. In the example they're almost the same, but you could also choose the outlet more upstream to delineate a subchatchment or choose a point where you measure discharge.
@@HansvanderKwast Right! I understand. Thank you.
Hi sir, can we find water quantity of river at specific point using this QGIS
You probably need a hydrological model. But you can calculate flow accumulation after rainfall making simple assumptions. Check for example the PCRaster Tools plugin, GRASS or SAGA tools.
may i ask what to do if the channel did not appear after run the upslop area?
If you use upslope it will not derive streams, but the catchment boundary. If it doesn't work, this can have the following reasons: (1) outlet not chosen on the delineated stream, (2) coordinates of the OTF projection of the project are not the same as the filled DEM, then the wrong coordinates are used, (3) the filled DEM was not used, but another input. I don't answer questions through e-mail without charging consultancy cost. You can post questions here.
@@HansvanderKwast i see ok2 thank you very much this is more than helpful thank you
Hi Hans, Thanks for the nice presentation and video. I have a quick question for you. Can you please let me know if the drainage files thus generated can be used for deriving linear and areal morphometric parameters like Stream lengths, Bifurcation ratio, stream length ratio etc.? My question comes from looking at the attribute table of of the drainage derived by the process outlined in your presentation. I have noticed that a stream segment consists of multiple segments. This makes the calculation of the abovementioned parameters difficult without merging/combining/dissolving the stream line segments.
Any thoughts on this ?
Hi Leena. I have a thought on this. Yes, the drainage file can be used to derive those morphometric parameters. Once the streams are generated you have to assign Strahler Order (number of stream)(often comes with the delineated streams anyways but you need to style them) to them . So based on the Strahler Order, you can calculate for example Bifurcation ratio (ratio of number of streams of a
particular order to the number of streams of the next higher order). You can also sum the stream length based on the Strahler Orders and so on. I hope this helps.
Just to add: each feature in the channels layer is a segment between two junctions (or spring/outlet) of the river.
Hi @@HansvanderKwast , and @Obinna, The problem I am facing is that each stream of a particular order is made of multiple line segments making it necessary to merge them before making any analysis. All of them need to be checked manually before merging to ensure that the number of streams of a particular order is not incorrect. This means going through the entire set of features for stream of a particular order. The number of features to be checked goes into thousands. Do you have any thoughts on how to get this done. ?
@@leenapande4127 The channels are created using the Strahler ordering method. See ua-cam.com/video/SuFl8EWDqfU/v-deo.html
This tags each segment with a Strahler order number. If you need something else, you need to do further GIS analysis or use another algorithm to create the river. If you want to have the whole river as one feature you can use dissolve. If you want each order, you dissolve on the order field (e.g. if you want to calculate total length of each order). You can also calculate the streams based on flow accumulation, which is explained here: ua-cam.com/video/aTYHpft1gus/v-deo.html
Hi @@HansvanderKwast Thank you for the reply. I am doing all this using SAGA tools. The whole river of the highest order needs to merged/dissolved in to one. The streams of each tributary (subsequent lower orders) should also be merged into one each. The number of streams segments is low in highest order streams. The number of line segments run into thousands as I go into tributaries (streams of lower order), which require manual selection and merging, which is time consuming. Do you think there is way out for this requirement ?
Many thanks in advance.
Sir what is the importance of minimum slope dialogue in fill sink by wang &liu method??
The minimum slope parameter in the Wang & Liu fill sinks algorithm is a user-defined value that determines the minimum elevation difference (and thus slope gradient) between adjacent cells in the filled digital elevation model (DEM). This parameter is important for hydrological modeling, as it affects the flow direction and watershed partition of the surface. If the minimum slope is set to zero, the algorithm will only fill the depressions until a horizontal surface is established, which may not be realistic or helpful for simulating water flow. If the minimum slope is set to a positive value, the algorithm will fill the depressions and also create a slight downward slope along the flow path, which may improve the accuracy and stability of the hydrological analysis. The optimal value of the minimum slope parameter may depend on the resolution and quality of the input DEM, as well as the specific objectives and assumptions of the modeling.