【作者】 夏东兴； 段焱； 吴桑云；

【Author】 XIA Dong-xing,DUAN Yan,WU Sang-yun(First Institute of Oceanography,SOA,Qingdao 266061,China)

【机构】 国家海洋局第一海洋研究所；

【摘要】 我国把海岸线定义为"平均大潮高潮时海陆分界的痕迹线",其长度以1:50000比例尺精度量算。但这条划分海陆的地理环境界线绝大部分时间是裸露的,1个月内海水可以到达的时间也仅有2～3h。人们为什么不以海水浸淹和裸露时间各半的地方划分海陆界线呢?究其原因,是因为陆生植物即便遭受短暂的海水浸淹也难以存活。实质上,海岸线是划分喜盐生物与淡水环境生物的界线,这是海岸线最基本的内涵。不同海岸地貌类型海岸线按以下原则划定:(1)具陡崖的海岸线位于陡崖与海滩的交接线,即后滨的后缘,是高潮时大风浪可以到达的地方。(2)具滩脊的海岸线在滩脊顶部向海一侧的大潮平均水位上方,激浪流或上冲流可以达到的最远位置;如果有潟湖发育,则潟湖岸线应量计在内。(3)潮滩海岸线附近的盐蒿、柽柳、芦苇等骤然减少,且植株变小,潮滩海岸线一般划在耐盐植物群落生长状况发生明显变化的地方;同样,发育潮滩滩脊(贝壳堤)的潮滩海岸,堤后潟湖岸线应列入海岸线计量。(4)在河口湾型河口(包括水域),岸线应划在河口区中段的中部。河口中段是过渡区,有一定长度,把水域岸线划在枯水季节咸水入侵界。如果用水的含盐度界定,即枯水季河口区出现水样氯度≤3150mg/L的位置,这是一个已使陆生植物完全不能成活的盐度值。(5)凡永久性的人工海岸构筑物,且构筑物所形成的岸线包络足够多的陆域面积,多为城市和种植用地,此构筑物形成的岸线即视为人工岸线。而一般窄而长的防浪、防沙堤或观光堤坝形成的岸线则不计入岸线统计范畴。盐田岸线的划分是个难题。盐田不能生长淡水生物,晒盐要引入海水,且一般趁涨潮自然吸纳或人工辅助吸纳。根据海岸线划法的内涵,应把有涨落潮水自然口门(潟湖口、湾口)纳水的盐田区划归海洋,岸线亦相对沿盐田边缘划出,如盐田区用地下卤水制盐则可例外。一般在海滩、潮滩上建的养殖池等仍以海洋对待。更多还原

【Abstract】 The coastline is defined as the mark line of the boundary between sea and land at high water level of mean spring tide,and its length is measured with the same accuracy as in a map of the 1:50 000 scale.However this boundary between sea and land in the geographic environment might be mostly exposed on the land and only covered by seawater for 2～3 hours once a month.Why not to take a line that is exposed for half of the time and covered for the other half as the of the land and sea? This is because the terrestrial plants are hard to survive even if they have been inundated by seawater for a short time.Substantially the coastline is a boundary between the environments for halophilous organisms and the environments for fresh water living beings,which is the essential connotation of the term.Therefore it is certainly related to the territory of human beings who determine the boundary delimitation.The coastlines with various physiognomies are classified according to the principles as follows:(1) For the coasts with cliffs,the coastline is located at the connection between the cliff and the beach,i.e.the landward edge of the backshore,where the strong waves can reach at high tides.(2) For the coasts with beach ridges,in general,the coastline is located right above the mean spring water level at the seaward side of beach-ridge top,the utmost position that surf or upthrust flow can reach.If lagoon is developed near the beach,the lagoon margin should be considered for the coastline delimitation.(3) For the coast with tidal flat,the coastline is located in the transitional zone where the growing condition for halophyte has changed and Artemisia halodendron Turcz.,Tamarix Chinensis Lour.and Phragmites australis become dramatically sparse and short near the coastline,where there is "a waste-deposit line" with fragments of plants,shells or other waste."The waste-deposit line" is formed by the waste pushed by uprush into the tide flat and settled down during the spring high water period,and it is a typical mark line.In the same way,if the coast is developed with longshore bar(a sea-shell bar) on the tide flat,the lagoon margin should be considered for the coastline delimitation.(4) For the estuarine coast including adjacent water area,the coastline is defined on the center of the middle segment of the estuary.In the upstream of the middle segment,the fluviation is dominant,while in its downstream sea action does,and in between,the middle segment is a transitional zone.Since the middle segment of the estuary has a certain length,the coastline is defined at the boundary where salty water reaches in the dry season,and it is close to the central point of the middle segment,where the outlet gets wider,with a certain distance form the tidal boundary in the flood season.If the salinity in seawater is used for the delimitation,the location where the chlorinity of the estuarine water is ≥3 150 mg/L in dry season will be the coastline.It is the chlorinity with which the terrestrial plants can hardly survive.For rivers with more silt in water such as the Yellow River,the river course is narrow,water drop small,and the distance that the up-bound tide covers is short,and the up limit of the tidal water in flood season can be considered as the boundary between the sea and land.(5) Artificial coast.If there are permanent artificial structures on shore that encloses a large area of land mostly with towns or cropland,these structures are taken as the artificial coast.But narrow and long breakwaters,sand control dams and sightseeing dams are not included in this case.The delimitation of the coastline of salt field,where fresh water organisms can not survive and seawater needs to be abstracted either naturally or artificially for salt production,is a difficult issue.According to the connotation of the coastline delimitation,the natural passages(lagoon outlet or a bay) of the flood or ebb tidal water should be defined as sea.Therefore the landward margin of salt ponds will be considered as the coastline.But if underground brine is used for the salt production,it will be an exception.The marine aquacultural ponds on beach or tidal flat generally belong to sea area.更多还原