Delineate watershed area in QGIS || Delineate catchment area in QGIS

hello and welcome back to another qgs tutorial here i will be deriving a watershed area in qgis using dem digital elevation model before we begin the tutorial we should have a clear understanding of a watershed area we have created a separate video with more information regarding the watershed you can follow the provided link in the description and friend you can practice the video by downloading the dem link in the description as well so now let's get started first load the dem from which we want to generate a water set or catchment area to where the dem go to layer add layer add raster layer and then select the dm of dm file you want to add after adding the dem let's check the crs of the dem for that right click on the dm go to properties and source in this type of analysis we need a projected coordinate system however we can see that the dm is already in projected coordinate system we don't need to convert the added gm to a projected one but if the dem is not in projected coordinate system we should convert it to the projected one for this you can go to raster projection and then select option wrap reproject after that fill the input layer with dem here we can see the target crs we will be selecting the projected coordinate system which in my case is utm zone 44 north for this click here and the easiest way is to filter the keyword here if i type 44 n i can see this option which comes in projected coordinate system you can find your desired coordinate system manually also by scrolling over here for now i will be getting my coordinate system by searching it here so let me select wgs 84 utm zone 44 north and then click ok after that click run and you will get the reprojected dm here in my case i already have the reprojected dm so i don't need to click run okay so is we have our data ready for the analysis let's proceed to the further steps now we will be needing a processing toolbox for this go to view panel and then select the processing toolbox you may have the processing toolbox by default also further to that we will use saga to fill the sync in added dem to do so navigate to saga and select terrain analysis hydrology then select fill sync wang and liu here this window will appear select the recently added gm from which we want to create a stream map save the field dm to the location of your choice to do so go here and select save to file and then navigate to the location where you want to save your field dm enter a name and then click save so after that uncheck both flow direction and water basin because we don't want them right now now press run button it could be a while depending on the size of the dem the larger spatial area may may take a longer time so friend after this we can see the filled dem after filling the sink for a stream order navigate to saga and then do terrain analysis select channel networks and drainage basin select the file on the elevation that is fill dem in threshold leave it to default or you can change the threshold uh value it's per the need you need a one if you need only measure measure stream increase the number of the threshold value if you need minor stream also decrease the threshold value here i will leave it to default except for the channel in strala order uncheck flow direction uncheck flow connectivity uncheck drainage basin and uncheck junctions also we don't want any of these analysis but remember to check the channel and and install order okay after that save the channel data for this navigate here and select save to file after we have found your destination location give the file name and then save it like this and press run so after pressing run it may it may take some decent time upon the size of your special area so friend after this process we can see the streams in the form of channel and strala order as well so before proceeding to make the watershed work catchment we should have a clear concept about it for for the example let's concentrate in this stream alignment here from this point a stream channel passes all the water which passes through this point is accumulated in certain area that certain area can be called waterside or catchment so now let's make a watershed or catchment of this point first we need to get the coordinate of this point here for this zoom the area of interest and here we can see the coordinate of a certain small pixel copy the coordinate and paste to the node the first one is x coordinate and the second one is y coordinate now go to saga train analysis hydrology and then select up slope up slope area here this window will appear give the coordinate value which copy we which we copied earlier give x coordinate value to target x coordinate and y coordinate value to y coordinate on the elevation select field dem on the method select deterministic 8 leave the rest to the default and hit run after this process we can see the water seed or catchment area for this channel outlet point here the extracted special area is in raster format we can convert this uh to save file also for this go to raster polygonize raster to vector here this window will appear in input layer select upslope area after that save save file by clicking here and select save to file after we after you have found your destination location uh give the file name and save save it and now we are ready to press run here we can see new save file data which include the delineated watershed area now get the watershed area only for this first make sure to check the toggle editing on on the recent shape file after that open the attribute table and find out which one is not watershed area here here are two two values okay here are two files in the attribute table here this one is in the watershed area so let's delete it from here after this close the attribute table and then turn off the toggle editing here we can see the watershed area our catchment with different if with the reference to this channel outlet you can use the data for several purposes and you can make watershed or attachment depending depending on your need of any catchment area or any watershed area that's all i hope you enjoyed the video you can learn more about watershed with the link provided in the description for any sort of problem you can comment in the comment box like and share the video subscribe the channel for the best qgis tutorial and lectures in spatial analysis have a good time happy learning

Channel: QGIS WORLD

Views: 56,262

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Id: CE7zZCkFbg4

Length: 9min 32sec (572 seconds)

Published: Thu Dec 16 2021