I have a set of polygons (include their elevation levels), representing geographical areas. I want to check which polygons will be inundated if a flat flood level is given. Lets say 1m flood from sea level, which is 0 m in this area. I was able to obtain/filter the polygons based on their elevation levels using query builders. However, this does not represent any sort of hydrological connectivity of these polygons. For an example, a low-lying area below 1m, surrounded by a ring dyke (dyke height above 1m, is also showing as inundated, with this method as this ignores hydrological connection and only consider elevation).

Is there any way that I can do this in QGIS and/or using others like GRASS or some tool? (except going for a dynamic hydrological/ hydrodynamic model like HecRAS)

Here, in the attached image, it is showing the polygons I have filtered from the whole domain, using elevation based filtering. Also, the rounded one is the problematic one, which indicates as inundated, but not hydrologically connected to other polygons. The middle white colour strip is a river stream, not included in the land area polygons


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