There is still no unified understanding of the concept of tidal flats or coastal tidal flats. It is generally customary to divide coastal tidal flats into three parts: ① Supratidal tidal flats refer to the muddy sedimentary zone above the average spring tide line; ② Intertidal tidal flats refer to the muddy area between the average spring tide high tide line and the average low tide line. , sandy and rocky beaches and other sedimentary zones; ③ Subtidal tidal flats refer to muddy and sandy sedimentary zones in shallow water below the average low tide line. This article uses this definition to determine the scope of coastal tidal flats, among which tidal flats have been reclaimed and utilized in the past 50 years.

As an important type of wetland, tidal flat resources are relatively fragile ecologically sensitive areas. The reduction and destruction of wetlands has led to frequent ecological disasters. Faced with the challenges of resource shortages, environmental pollution, ecological damage and frequent disasters, whether wetland is a natural complex (such as a land type), a multi-functional ecosystem or an object Human beings pay great attention to the diverse human living environment. Since the signing of the Ramsar Convention in 1971, especially Agenda 21 and the Convention on Biological Diversity, governments of various countries have attached great importance to the protection of wetlands, and land-based research has attracted increasing attention.

Looking at the history of Zhejiang's tidal flat changes, in the early days it was mainly an intertidal shoal on a muddy coast. With reclamation and development, the tidal shoal developed into a coastal wetland, and then evolved into reclaimed cultivated land (or solid land). knot land). The remote sensing survey on the current status of tidal flat utilization used Landsat-7ETM+ satellite data in March 2001, and partially used OT-4 panchromatic band data. On the SPOT-4 and ETM+ multispectral data fusion and ETM+ self-fusion images, reclamation and various utilization situations (such as aquaculture, agricultural planting, salt fields), etc. can be identified (see Figures 4.8 to 4.13). 〓From the characteristics of remote sensing images, there are many land object units that can be distinguished in the coastal zone. Based on the actual survey conditions, the resources are divided into three types from sea to land: intertidal zone, coastal wet zone and reclaimed cultivated land. The wet zone is divided into salt culture ponds and reclaimed wetlands. The mixed zone of culture ponds and reclaimed wetlands is collectively called coastal wetland (Figure 4.14). It should be pointed out that due to the influence of changes in hydrodynamic conditions such as tides and wind waves, the intertidal zone may sometimes swell and sometimes erode. The range of the intertidal zone shown in the figure mainly reflects the interpretation results of satellite images in March 2001. .

Figure 4.8 Remote sensing image of tidal flats

Figure 4.9 Breeding pond The images of various types of breeding ponds are also very different. The shrimp and crab ponds are relatively small. The image is marked as a shallow pool

Figure 4.10 Breeding pond The fish and shrimp polyculture pond is relatively long, while the shrimp and crab pond is relatively small. It is clearly visible in the image

Figure 4.11 Reed marsh is an important part of the wet zone, and its image is significantly different from the intertidal zone with almost no vegetation and the breeding pond completely covered by the water surface

Figure 4.12 Reclaimed cultivated land evolved from coastal wetlands and has now been consolidated into land.

This is a remote sensing image of a cotton field

Figure 4.13 A remote sensing image (a) and a photo (b) of a salt farm located north of Gongyu Village in Xiangshan County