近百年来洞庭湖堤垸空间变化及成因分析

系统分析洞庭湖堤垸的空间变迁规律对于阐明湖区调蓄水量的变化原因及其洪涝灾害的形成机制具有重要的意义。以《洞庭湖历史变迁地图集》为基础，运用ArcGIS的空间分析技术，对洞庭湖民国前期（1921~1930年）、民国后期（1930~1949年）、解放初期（1950~1963年）、20世纪70年代（1963~1980年）和现状（80年代至今）5个时期的堤垸演变进行了研究，详细分析了其空间格局的变迁规律及其成因。研究结果表明：自民国以来洞庭湖的堤垸面积虽不断增加，但速率明显减慢，从最初的3126%减缓至现在的273%；民国前期洞庭湖堤垸面积为5 08419 km2，民国后期所围堤垸主要集中在沅江中东部；至解放初期，通过兴建国营农场，并且在大通湖及西、南洞庭湖进行围垸，堤垸面积增加至8 10210 km2；至20世纪70年代，堤垸扩展部分主要集中在湖区西北角；近30 a来，由于“退田还湖”政策的实施，堤垸面积及其分布相对变化不大

SPATIAL CHANGE OF POLDER IN DONGTING LAKE DISTRICT AND ITS DRIVING FORCES IN THE LAST CENTURY

Systematic analysis of spatial change of polders is very important for revealing water storage change and flood occurrence in lake areas.This paper addressed spatial and temporal changes of the polders in the Dongting Lake in the period from 1921 to 1990s.Historical maps of the polders were digitalized for the five periods and change detection analysis were performed.The five periods include 1921-1930,1931-1949,1950-1963,1964-1980 and 1980s-1990s.Our main conclusions are as follows. (1) From an aspect of temporal change,the polders showed 〖JP2〗an increasing trend from 508419 km2 in 1921-1930 to 909813 km2 in〖JP〗 1980s-1990s.In spite of this,the polders changed with spatial and temporal differences.The ploders expanded at a rate of 3126%,3122%,1198% and 273%,corresponding to an annual rate of change of 313%,312%,1198% and 034%.In contrast,the polders diminished in some areas at a rate of 1268%,1370%,340% and 000%,corresponding to an annual rate of change of 127%,137%,024% and 000%.The largest change appeared in the shift from the first to the second period,during which land reclamation was excessive but effective management was lacking.Since then,the polder reclamation was replaced with maintenance and the polder areas remained stable with the policy of “returning farmland to lake”.(2) From an aspect of spatial change,the polders expanded generally and encroached on Dongting Lake.In 1921-1930,the polders were mainly distributed in the northern part of the lake area in a relatively sparse form.In 1931-1919,the polders appeared to intersperse with each other and the newly constructed polders were mainly concentrated in the central and eastern part of the Yuan River.In 1950-1963,the polders expanded in high elevation areas and the areas surrounding Datong Lake,the south and the west Dongting Lake.In 1964-1980,the polder expansion mainly appeared in the northwest corner of the lake area.In 1980s-1990s,the polders increased very slightly.Our analysis supports that excessive reclamation caused serious shrinkage of the lake water surface.Because Dongting Lake plays an important role in regulating the Yangtze River and flood prevention and has important ecological and environmental values,it is of priority to restrain lake reclamation and encourage the returning farmland to lake.In addition,our study should be valuable for understanding the water storage variation and floodings in the lake area,which needs further investigation