Dear GIS experts,
I would be very thankful to receive your help/support/suggestion for solving my following problem. I'm using ArcGIS 10.1 with Spatial Analyst and 3D Analyst(no ArcInfo license) and Arcview 3x (still for many plusses).
I have a river network - both a shape file and raster grid - generated from a DEM through Flow Direction and Flow Accumulation grid for a very big region (a country).
What I want to know/calculate is - for every river cell, what is the difference in elevation value between the elevation of that river cell and the elevation of the river cell at a given distance (say, 1 km, 2km, 5km) downstream from that river cell along that river i.e. flow direction?
I tried to do this by using the focal statistic function running over the River-DEM (using minimum as statistic) and then subtracting the resulting grid from the original River-DEM; but this dos not work completely correctly because at many places the minimum in the neighbourhood is found in the adjacent river (tributary or another parallel river at another side of the ridge) and it gives me wrong elevation difference because the minimum river cell is not in the same river downstream but in another river although within the defined search/neighbhourhood distance. How can I get this correctly- i.e. the elevation difference in the same river downstream in a given distance?
I hope that I could make this my problem sufficiently clear. What would be your suggestion to solve this?
Thanking you a lot!!