Need to find area around polyline shapes

[Cathina_Gunn_de_Rosas]

I have a couple of river basins defined by flowlines and the flowlines are split up in to small sections called subbasins ... I need the area associated with each of these subbasins ... what would be the simplest and quickest way to get this?

I've attached a screenshot of one of the basins with the flowline sections so you can see what I mean.

[JoeBorgione]

If you have access to the DEMs or some sort of terrain grid for you basins and subbasins, that would be the best, fastest and easiest.  Otherwise, looking your attachment, I'd say roll you sleeves up and start digitizing them...

[LeonardoCarvallo2]

In my opinion to be working at the level of sub you need to properly deliminar the area occupied by each to obtain a conclusion, I recommend you put as a base layer contours and Digital polygons taking into account the division of water, this way you'll know exactly and precisely according to the terrain surface of each sub-basin. Good Luck!