Also as a hydrologist, I can see the benefit of Bryan's request. I could imagine a process like this (though I don't know how to achieve step 4 in Manifold) 1. run the watershed prep tool to fill depressions 2. run the watershed lines tool to create flow paths 3. check and correct flow paths if necessary 4. trace along the flow path lines from most upstream to downstream, and make sure that elevations decrease monotonously. If not decreasing, reduce the DEM elevation to match the upstream value, within a specified/calculated width. This would remove any artificial dams from the data, and also cut through bridges which might be shown in the lidar, allowing the resulting DEM to be used in a hydraulic flood model such as TUFLOW or MIKE
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