Use a long thin cable on a motorized spool. Rig up a waterproof reinforced box with sensors that detect speed and direction (mercury switch type deals?... I don&#x27;t know but I bet there is something). Hook them up to a board with some storage. Drop the box in and start reeling the cable off. If the cable goes slack the thing has probably stopped. Maybe it&#x27;s hung up. Pull it back a bit and try again. If it keeps stopping in the same place it&#x27;s probably all the information possible by this method. Retrieve the box, get the speed&#x2F;direction information, do some distance calculations and graph it. Ideally the box will go all the way to the exit point and you will have a profile showing where the water ends up. But even if it doesn&#x27;t, you will have a good idea of direction and depth the water is traveling for a certain distance at least. This will at least make better guesses in the future.