FEATURES OF HAINAN ISLAND COASTAL ENVIRONMENT

Hainan Island is located on the northwest of the South China Sea,belonging to tropical monsoon island climate,changing in half year period.The island is warm all the year round and accepts much sunshine.Hainan is a South China Sea shelf island,with mountains in the middle and multiple coast types along the edge.Its basement is pre Devonian sandy shale and metamorphic rocks,which became hard and rigid during Caledonian movement,and then late Devonian, Carboniferous-Permian sandy shale,limestone,clastic rock and carbonate rock in sea land alternations.The rivers are fed by precipitations,have their sources in the central mountains and radiate into sea.There are 1 510 single current streams that provide rich hydraulic resources but in uneven distributions.The island mainly has 5 natural resources,namely,agricultural and tropical economic plants,mineral resources,oil and natural gas,touring resources,aquatic products and estuarine resources.Hainan mainly owns bedrock embayment coast,with a 1 528 4 km long coastline,64 estuaries and more than 300 islets.The tide is characterized by solar tide.The east and south parts of the island see irregular mixed tides,with solar tides for 15～18 days and semidiurnal ones for 11 days on the average;the west and north coasts see regular diurnal tides,with tidal range of 1～ 3 m. The island coast has been influenced by both tectonic movements and climatic changes.For examples,in the early time of Pleistocene,the coast belonged to bedrock embayment type,and during frequent tectonic movements in late Pleistocene,some bay floor was uplifted and became terraces;the tectonic uplifting movements lasted until Holocene when some coral reefs were uplifted to several meters higher than the sea level.Coast can be grouped under bedrock embayment and sandy gravel plain coast types according to origin and forms.Tidal actions have also played an important role in the evolution and utilization of the island.Tidal branch estuaries are on a large scale and covering a water area of up to several tens of square kilometers.