11.1 A pebble is dropped into a stream of water that flows in a rectangular channel at 2 m depth. In one second, a ripple caused by the stone is carried 7 m downstream. Determine the speed of the stream and whether it is subcritical, critical, or supercritical. At another location the ripple moves downstream 11 m. Determine the speed of the stream and whether it is subcritical, critical, or supercritical at that location.