The pilot was departing a remote tidal beach in a tricycle landing gear-equipped airplane. The pilot reported that during the takeoff roll, right at liftoff, the airplane hit a piece of drift wood jamming the elevator in the nose-up position. As the airplane became airborne the pilot reduced power in an effort to control pitch. At about 15 feet above ground level the elevator broke free, and locked in the nose down position. The airplane impacted the beach sustaining substantial damage to the firewall and left elevator. The pilot stated that there were no preaccident mechanical anomalies with the airplane that would have precluded normal operation.