I am trying to graphically depict the exact amount of irrigable acres from a single point, in this case a headgate from a drainage ditch. Basically, I have the original water right decrees (i.e. confusing legal documents) from the late 1800's and am interested in accurately illustrating the legally allowable area to which they can irrigate.
Example: From the stream a drainage ditch runs west for 1 mile (on contour) before it opens into a small pasture, irrigating 50 acres below its outlet.
Is there a way to show this acreage below this specific outlet point? Perhaps a sort of reverse Snap Pour Point operation? Some function that fills in a specified area below a certain point, following topography lines?