 Hello, this is Hans van der Kras, senior lecturer at IHE Delft Institute for Water Education. In this video I'm going to demonstrate how to use the lake flood tool from the Processing Toolbox. It's a SAGA tool. To use this tool we start with a lake polygon and digital elevation model. And in raster analysis it is very important that the inputs, the raster inputs have the same dimensions. So we are not going to use the rasterize function for the lake but we are going to use the clip function from SAGA, just to make sure that the rasters that the tool needs have the same dimensions. So go to the Processing Toolbox and we search for clip and there are many clip functions but we use the clip raster with polygon from SAGA, the DTM as an input and the lake polygon as a polygon that we want to use to clip and let's call the output lake raster. In this way we are sure that the clipped raster has the same properties and there is the result. Now we go to the raster calculator and we are going to add the lake raster and we say if it has values, so let's say larger equal than minus 9999, put it in brackets then if that is true then do times 100, so if it's true it's 1 and then all the values will end up with the value 100 and if it's false it will be 0 and then times 100 will be 0. So this will result in all the lake pixels to have a value of 100 which will be our first lake level that we are going to use for the flooding. Let's save the output and let's call it level100.tiv and now an important step we need to choose the layer extent of the DTM, otherwise it will have not the same dimensions and we can't use it in the tool later, it will give errors. Now we have all the inputs for the tool, so the tool we are going to use is the lake flood tool from SAGA. Here you see that our level100 has no specified projection, so let's specify it first as good practice and then use the lake flood tool. As an input we use the DTM and we are going to flood it from the level100 pixels and let's call the output of the lake that it will create lake100, that will simply be the elevations of the lake and flood 100 for all the areas that are above the flood line. There we go and of course it makes more sense if we are going to style it, so I choose single band pseudo color and what I would like is to have all the flooded pixels blue and everything that's above to have the elevation model colors that we have below. So if I use this clip out of range values to make sure that everything above a certain value that I specify will not be visualized. So let's use that to create classes and I use here a value of 100 because that was our threshold for the flood and then everything that is flooded will have value 100 and all the other things are clipped to the elevation, but the elevation model is not stretched in a way that we can see a lot of elevation differences so let's also stretch it from value 100 to the maximum and in this way we see now the area that is flooded and I can repeat the steps for different flood levels and here you see the result. So with these tools we can flood from specifying a certain lake level and then visualize it in a proper way to see which areas are flooded. Of course this can't replace a full hydraulic model, it's a quick indication to simulate inundations. I hope you liked the video, if you want to see more of these videos please subscribe to my YouTube channel and for free tutorials have a look at GIS OpenCourseWare.org.