Great Falls of the Potomac after heavy rains, Virginia/Maryland, 1969.
Taken at Great Falls Park in Virginia, but the state line is the southern bank of the Potomac, so both states are included in the picture. The use of so-called "natural boundaries" is irksome, for exact plotting of where the boundary falls when using rivers is extremely difficult. Midpoint, normal flow, highest possible flow, or lowest water? It can add or subtract many meters when a stream has variable flow. At least the Potomac is constrained by the geology at the Fall Line, and the channel is unlikely to shift. On rivers like the Missouri or the Mississippi where there is a large, flat floodplain, the river channel can shift by kilometers. There are lots of illustrations of bits of territory left on one side or the other after a shift. One example is provided by the boundary between Nebraska and Iowa near Omaha Airport. A slice of Iowa is now stranded on the Nebraska side thanks to an official boundary designation based on the old channel. The confusion is simpler here - where exactly is the southern bank and therefore where does Virginia jurisdiction end and that of Maryland begin? Pictured is a side channel which is frequently dry at low or even normal flow. The main stem of the river is several meters to the right of the photo. Which is used to define the boundary?
