I am wanting to determine the area that would have been inundated by past flood stages of a river. I know the additional heights I wish to add, and I have a DEM (ASTER v2; I know it isn't that good, but this is outside the US so SRTM is degraded to 90m). I am wanting to evaluate a very long stretch of river (ca. 1400 km) so simply taking the river elevation at the upstream location and adding the desired flood height for the entire length is not possible (given the river elevation drop over such a long distance). I have had two ideas about how to proceed.
1. Segment the river into smaller units and simply determine flood heights by adding to the local river height.
I am not wanting to use that method because it seems a bit ... cheap.
2. Overlay a polyline for the river centerline. Find the cell with the lowest value within 30 meter distance of the centerline. Add flood height to that cell and identify all cells within a given window that have a lower value.
I am thinking that option 2 is the more efficient and defensible method, however I do not know how to go about DOING it. Any direction that someone can give about how to learn to do so would be most appreciated. If you have an idea of an alternate way to achieve my ends, I am certainly open to that as well. Thank you.
1. Segment the river into smaller units and simply determine flood heights by adding to the local river height.
I am not wanting to use that method because it seems a bit ... cheap.
2. Overlay a polyline for the river centerline. Find the cell with the lowest value within 30 meter distance of the centerline. Add flood height to that cell and identify all cells within a given window that have a lower value.
I am thinking that option 2 is the more efficient and defensible method, however I do not know how to go about DOING it. Any direction that someone can give about how to learn to do so would be most appreciated. If you have an idea of an alternate way to achieve my ends, I am certainly open to that as well. Thank you.