Such streams are known as pool and drop rivers, as opposed to continuous. See Continuous . Pourovers are rocks with flat tops that are just under the surface of the water. Occasionally, pourovers also come complete with sharp surfaces capable of putting new holes in boats. Generally to be avoided unless you're sure of what you're doing.
Rocker refers to how curved the bow is along the keel line.
As expected, no rocker produces a fast canoe that loves to go straight, a nice feature when touring on large lakes. A heavily rockered boat will turn on a dime, but will not track well. Most recreational canoes will have a slight amount of rocker and a straight keel line. There are also some nice waves and other features out in the less-crowded main channel. Water going through a very narrow passage between two rocks at high speed.