The 72-hour sport pilot initiated a descent to an open field where he intended to perform a touch and go landing on his registered powered parachute. While at 100 feet above the ground, the powered parachute encountered severe turbulence and the powered parachute entered an uncontrolled tight spiraling descent from which the pilot was unable to recover. The pilot, who reported having accumulated a total of 4 hours in the same make and model was seriously injured. The 15-statute mile flight was planned as a flight of two Rotax 582 powered parachutes. The pilot stated in the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) that he had "no memory of the flight;" however, a witness who was flying the other powered parachute, was able to describe the accident sequence. The witness stated that the accident pilot was flying approximately 100 feet above the ground while maneuvering to land, when "he encountered severe turbulence causing the powered parachute to go into a tight spiral." The parachute impacted the ground at a high rate of descent, which was described to be "approximately 40 miles per hour descent rate." The weather at the nearest weather reporting station located approximately 9 miles to the northwest of the accident site, reported the wind from the east-northeast at 6 miles per hour, clear skies, visibility 10 statute miles, and barometric pressure setting of 29.93 inches of Mercury.