I would think that "valley" does not include the basins of major tributaries to the river, while basin is the entire drainage area of a river.I think that in boundary determination, "valley" and "basin" are used pretty interchangeably... one possible exception would be where a tributary passes through a water gap - e.g. the Valley of the Danube in Wallachia would include the basin up to the crest of the Carpathians, but would not include the basin of the Olt that lies on the north side of the ridge...