I'm studying the drainage of a lake and I have a DEM of the lake and the surrounding area. I already identified the shorelines of ancient lake levels at higher elevations, but I would like to keep draining the lake digitally to predict future drainage patterns. The DEM shows the even lake surface, although I have a bathymetry map which shows the depth of the lake bottom.
What can I do to lower the DEM surface to include the bathymetric information? Is there a way to overlay the bathymetry map and create polygons for the various depth contours, then use those polygons to assign new elevations to the areas within them on the DEM?
I have access to both qgis and ArcGis.