Automate Stream and Catchment Delineation in QGIS with the Graphical Modeler

hello this is hums from across senior lecturer at IG Delta Institute for water education in this video I am going to show you how to automate the stream and catchment delineation procedure using the graphical modeler in kuja's so we need to prepare some data before we get started I need the DM tiles and a bounding box for the study area here F for DM tiles from srtm and in the processing toolbox I go to create model and then I end up in this window with the processing modeler and I give the tool a name and a group to which this tool will be added in the processing toolbox after we have saved it and then I'm going to define the inputs and you can of course identify each raster layers separately but I use here the multiple input and I give it a name the DM tiles and make it a raster type so you can only open their a set of raster layers which are DM tiles then we also need a vector layer which is the bounding box defining your study area and choose for a geometry type polygon and then we click OK then we can add the algorithms now first we go into mosaic so I built a virtual Ruster and these are the same tools as you find in the processing toolbox but you can give them different names I call it mosaic TEM tiles we use the DM tiles that were defined as a variable then we put the same things there as we would normally do so we don't want the layers to appear in separate bands then the next algorithm is warp to change the projection we project and we can clip also at the same time with this tool so we project and clip the DM as an input layer we use the output from mosaic DM tiles I define here the output project but I can also use that from the bounding box because that's the projection we're going to use and I set a no data value and the output spatial resolution I set it to 30 meters which is approximate for the SAR TM one arcsecond product I switch on the advanced parameters and there I use the extent of the bounding box as the geo-reference units of the extents of the output and the next thing we can do is to fill the no data so fill the voids they might be in your DM maybe they are there maybe not but anyways we we cannot differentiate there so we'll do that anyway that's step I increase the distance and that's okay you see it nicely adds these functions and connects them to each other and to the input data then we have to fill the sinks and I'm going to use the run a new algorithm make sure we use the output from The Voice and we can output here the filter DM and not the other ones if we define an output that means and that it will be saved on your disk and identified as an output file and it'll be a green box in the scheme and make that an output because we need it later then I want to add another input variable which is the strata or the threshold which you can determine before or you can calibrate it [Music] strata orders always have a minimum value of one and I put a maximum of 20 and a default of 8 then I can add the channels and drainage network algorithm use the output a fill DM and then refer to the straddler threshold input variable and it will output all these layers with what I need as a real saved output are the streams so this algorithm will output the filled DM and the streams then I would like to define a vector layer with the outlets as an input and normally yeah you can identify the point on the map but it needs to be snapped to the delineated channel so the streams file here so I'm going to use the snap geometries to layer and rename it snap pour point that's how it's called in some other software and as an input layer I use the outlet on map input and the reference layer the channels so it will snap to the channels and we can put there our tolerance but it's also nice to make it variable and I need that as an output this is an apt outlet you can move these boxes and they still remain connected actually I don't want that as an output I want to identify the tolerance and make that variable and here you can define it in a meter so between 1 pixel of 30 meters and 5000 meters will be okay I can edit this function and make it refer to the right input which is the tolerance and another thing I want is the geometry the X&Y coordinates so I need to add another algorithm and there is add geometry attributes I do that because in the next step we need the coordinates of the X and the y of the point to delineate and the catchment belonging to that snapped outlet point so call this one safe outlet with coordinates the input layer is the snaps geometry and then we can define here the output layer call it snapped outlet there it is so three outputs for this algorithm filled diem streams and snapped outlet save it give it a name goes to my profile by default to hide all layers because I want to identify now the outlet on the OpenStreetMap so as an input we need to define the outlet before we run the algorithm so I want to delineate the Ruhr catchment the same one is in the manual procedure I create a scratch layer with the point geometry in the correct projection that's important click OK and I add the point at the place where the Ruhr comes into the mouse River save it and then I find the model under models hydrology stream delineation I choose the bounding box I choose the DM tiles now outlet stralla order I increase the tolerance here because that's needed and I leave the others open to us temporary output and then it runs our model gave an error but it's still computed zoom to the area and because we didn't specify output names it will just give some default names but segments are our channels and it can style it there it is and a filled DM now I want to make a second model to delineate the catchment because this one delineated the streams but I need that as an input to delineate the catchment let's have a look at the snapped outlet how that worked so it moved the outlet to the line so I'm going to create a new model I call it catchment delineation and I put it also under hydrology and there I need a few inputs I need the raster layer it's the filter DM of course as an input I need a number which is the x-coordinate I don't put striction is there because I wanted to be a generic tool for any projection that you want to use and any location field for the y-coordinate and we use the upslope area tool to calculate the catchments I'm gonna rename this to delineate catchment take the x coordinate and the y coordinate from the variables that we define elevation filled DM and we use here the default methods and that then generates the delineated catchment however we don't want the roster we also want the polygons so I'm gonna use the polygon eyes and rename it polygons eyes catchment make sure to choose the upslope area output keep the defaults remember that we have two attributes in our attribute table of the polygon eyes catchment where only value 100 is the catchment so I'm going to use here extract by attribute and I call it safe catchment polygon only and I type here the field name and it's their operators equal and then hundred so I only select value hundred from the DN field which is the field which we created previously and then the output is the catchment boundary and that will be then the result I save the model and I can now run the model so run catchment delineation I used a fill DM now I can use the coordinates from the attribute table of the snapped outlet simply place them here and I leave that as default run the algorithm ends up with the catchment I click zoom to layer you can now see that it delineated the whole route catchment as a polygon and that's what we wanted so with 2 added tools we can do the whole procedure of catchment delineation and you can continue styling that in there if you want to make a nice map I hope you've enjoyed this video please subscribe to my youtube channel for updates for more free materials on GIS please have a look at IG Delft opencourseware at des opencourseware at work

Channel: Hans van der Kwast

Views: 3,799

Rating: 5 out of 5

Keywords: QGIS, catchment delineation, watershed, graphical modeler, processing toolbox, SAGA, hydrology

Id: BKdJMGXgOzg

Length: 14min 16sec (856 seconds)

Published: Fri Apr 10 2020