1. An apparatus for capturing and analyzing video images of river, lake, or sea bed sediment containing grains of various sizes from the bottom of a body of water, said apparatus comprising: a video imager, including a flat field close-up focus lens, for collecting images of bed sediment containing different grain sizes; a waterproof housing containing said video imager; a weight member associated with said housing for ensuring that, in operation, said housing can be lowered down to the bed sediment; and a video recorder for storing the images collected.