I am trying to extract longitudinal profiles for a series of rivers in mountainous terrain from SRTM 90 data. In places where there are deep, relatively narrow canyons, using Fill within the Spatial Analyst - Hydrology tools fills these canyons, making them instead large flat areas. I've attached an example of my original dem, the result after filling, and the resultant flow accumulation grid (with only cells greater than 1000 colored). The relief is relatively extreme ( in excess of 2000 meters of elevation change within 1 to 2 kilometers of map distance). Is there a work around for this error? I need the flow accumulation grid as an input for another program that extracts longitudinal profiles and allows me to calculate river concavity, etc. so ideally I need a way for the flow accumulation grid to be accurate.