 Hello, this is Hans van de Kwaas, senior lecturer at IHE Delft Institute for Water Education. In a previous video I have demonstrated how to use an existing river network to burn into a digital elevation model in order to have the water following the real hydrography in the study area. That method used the r.garve function from grass from the processing toolbox. Although that works fine, it's also good to know how you can easily do it yourself by applying map algebra functions. In this video I'm going to show you how to do that using the Raster Calculator and other map algebra tools based on a method described by Case Vesseling, Willem van Derers and Marcel DeWitt that have applied that in the PC Raster language for the Rhine Basin. So we start with SRTM-DEM, styled here with a hill shade and we use the Rural River from OpenStreetMap. The first thing we need to do is to Rasterize this river. So in the processing toolbox we look for Rasterize and we find this Rasterize function and we fill in the form, we burn a value of 1 for where the river is, we use geo-reference units and make sure that it has the same dimensions as the DEM otherwise it's not going to work. So 30 by 30 meters and we choose the extent from the DEM because it's a Boolean map with only once in this case we use the byte output data type and we save the Rasterized file to Rurasterized.tiff and then we run it and there it is, drag it to the top and we can now style it. It's a palleted unique values because it's a Boolean with only once in it as we can see we make them blue, so now the river is blue and if I remove the river on top and we see now it follows the original vector but then one pixel wide. The next step is to get the zero values back in because we are going to need that in the equation. So we use the reclassify values function from saga, it's a little bit of a trick to get the zeros back in so make sure you choose the Rurasterized as a method, we choose simple table and we fill in the lookup table that the ones just stay one and we put that operator on option number one and we're going to replace the node data values with zero and we keep the rest as it is, so the ones will be one and the node data will be zero and then we save the reclassified grid and we run it, click close and there we see it, let's style it, I find it good practice to style to make sure that you made the right calculation, you can find that by visualizing it, make the ones blue and zeros red, the idea is to make a normalized DEM therefore we need to know the statistics, the minimum and maximum values of the DEM, so in the toolbox we choose the Raster Layer Statistics function, choose the DEM, we can keep it as a temporary file and this will generate an HTML file, if we click the link it will open in your browser and we see there the minimum and maximum value of the Raster of the DEM, we make a note of those values, now we're ready to calculate the standardized DEM, so I go to the Raster Calculator and we create this equation using the minimum and maximum value of the Raster and we save it, let's call it stddem.tiv where we do okay and there's our standardized digital elevation model with values between zero and one, now we have the standardized DEM, we can burn the river in it, so we simply subtract the Rasterized Boolean River that we created before, so where the river is value of one will be subtracted and where there's no river it will remain what it was, so the river will always be deeper and there we go, this is then the burned DEM and then the final step is to multiply the original DEM with the standardized DEM and in that way we have corrected the DEM values with the ones that are burned by the river and there it is, so let's style it to see what the result is, let's choose single-bamp pseudo-color, it's continuous data and we choose CPT city, elevation and there we are, we need to change the stretching of the colors, updated canvas and there we see that indeed the river is deeper than the environment around it which will make the water flow to the river, so with this you can continue the steps for filling the DEM and the other steps needed for catchment delineation as explained in the other videos, I hope this was useful and that it improves the delineation of catchments.