OT:ideas for oblique view tide-gauge ?

So not directly over tidal water , viewing horizontally the rise and fall of tidal water over mud flats. There is a change in light level , excluding fog, between veiwing the mud and veiwing the water. Night time there is a lot of street-light spill over , if moonless. Perhaps a web-cam , with masked off view of a vertical slot with range of angle from about -2 degrees to the horizontal , to about -50 deg, with no boats, reed-beds or anything else in the view, just mud or water. I assume it would be possible to digitally determine the "terminator" as it moves up and down and initially generate a look-up table comparing to a proper tide-gauge nearby, for the heights corresponding to the image. Any other ideas?