Study On The Expansion Of Reclamation And Land Use Changes In Hangzhou Bay

Since the 21st century, with the accelerating steps of industrialization and urbanization in China, especially in the east coastal zones, more and more people have migrated to coastal zones, which cases the shortage of land there. The prominent conflicts between man and land have brought great challenge to the sustainable development of society and economy in the coastal zone.In this case, as an important potential land resource, tidal flat caught much attention of human. During the past several decades, a large-scale tidal flat reclamation has taken place in China, and brought huge social and economic benefit, but also a series environmental and resource problems. Therefore, it’s necessary to do some research on the temporal and spatial change of coastal saline resources.This paper takes the reclamation area in Hangzhou Bay as the study area, using a time-series Landsat images to investigate the expansion and land use change of reclamation area from 1970s to 2014.Select Cixi (a county in Ningbo) as the typical area for further study according to the extent of reclamation changes. Then extract the data of typical area in form of GF-1 image in 2013 by using object-oriented classification method, and the results are applied to study land use structure and used for assessing Landsat images and land use change survey. Finally, hotspots analysis is performed to find the tidal flat utilization patterns in Hangzhou Bay. The results are shown as below:(1) Through the analysis on the dynamic change of reclamation projects in Hangzhou Bay, the result shows that the total reclamation area in Hangzhou Bay is 851.03 km2 from 1975 to 2014, and the annual speed reduced first and then increased on the whole. In terms of spatial distribution, the change of coastal line mainly occurred on the south bank of Hangzhou Bay.(2) Through the analysis on land use change of reclamation area, the result shows that the main land use type was unused land and pond during the 1970s and 1980s, because the land was unable to cultivate for the soil didn’t have enough time for salt washing. As time went by, the desalting of soil and the dramatic needs of land have led the pond and cultivated land keeping increasing and becoming dominant land use types. Specifically, this part summarized the characteristics of reclamation dynamic changes in three aspects:Firstly, due to the limited area and time, the land utilization was relative simple, and land use change was generally one-way conversion from year 1980-2000. Since the year 2000, as the land utilization diversified, the land use changes became multiple-conversion. All the classes enlarged except unused land. Specifically, the new reclamation area was mainly pond and cultivated land at early stage. From the year 2000, the construction land increased a lot, until 2010 the annual increasing speed of construction land tend towards stability, while pond became the highest one.Secondly, the change rate and dynamic degree of the integrate land use in the period 1980s-1990s reduced for the restriction of resource reserve, technique and policies. Since the year 2000, the utility of tidal flat in Hangzhou Bay significantly enlarged as the development of society and economy, policy support and urgent demands for land resources.Thirdly, unused land conversion output was more than other types, the main flow of the unused land was the conversion to cultivated land and pond. And there was frequent bidirectional conversion between cultivated land and pond, showing balanced conversion. While the main source of conversion to construction land was cultivated land and pond(3) According to the classified image in Cixi County based on GF-1 data, the result shows that the main land use types were water and farmland. Pond was the main type in water, while grassland was the main type in farmland. Among construction land, industrial land, road and hard ground were higher than other classes.Moreover, as GF-1 data have more texture information than Landsat OLI data, we can conclude that domestic high resolution images have great potential in the application of coastal land use detection. By using the classified result of GF-1 to assess the result of land use change survey, the accuracy of buildings is relatively low while the classification of main roads is much more precise.(4) Through the hotspot analysis of tidal flat resources utilization, it shows that the main utilized classes in Hangzhou Bay are water and farmland. And the classes of the same land use degree tend to aggregate. Water and unused land mainly sited nearby the ocean, while the construction land mainly sited nearby the inland.