RESEARCH OF SEVERAL PROBLEMS ON MOVEMENT CHARACTERISTICS OF COASTAL DUNE SAND——AN EXAMPLE FROM THE SOUTH COAST OF MINJIANG ESTUARY

The threshold velocity of sand is influenced by many factors in coastal zone, but the grain diameter and moisture content of sand grain are the dominant factors. Along the south coast of Minjiang estuary, the mean grain diameter of beach sand is 2.0 Φ and the moisture content of beach sand is almost from 0.3% to 3.2%. Caculated by Johnsons experimental equation, the threshold velocity of movement on the beach is 6￣7 m/s. The result coincides with the field observing value very well. On an equal basis, the threshold velocity of sand in coastal zone is much higher than that of sand in inland desert. But the rate of sediment transport in coastal zone is much less than that in inland desert. They have close relationship with the environmental factors of coast. The coastal zone is the belt where the wind velocity changes radically, so the wind velocity record of land meteorological observatory should be corrected when we use it to analyze the wind regime and study the sand transport in coastal zone.