**6. References**

212 Hydrodynamics – Natural Water Bodies

Moreover, corresponding to the wave-frequency peak and low-frequency peak of the frequency spectra of the cable tensions, there occur the wave-frequency motions and lowfrequency motions in the tunnel element. This also reflects directly the interrelation of the

The motion dynamic characteristics of the tunnel element and the tensions acting on the controlling cables in the immersion of the tunnel element under irregular wave actions are experimentally investigated in this chapter. The irregular waves are considered normal incident and the influences of the immersing depth of the tunnel element, the significant wave height and the peak frequency period of waves on the tunnel element motions and the

As the immersing depth is comparatively small, the motion responses of the tunnel element are relatively large. Besides the wave-frequency motions, the tunnel element has also the low-frequency motions that result from the actions of cables. For the sway of the tunnel element, for different immersing depth the low-frequency motion is always larger than the wave-frequency motion. While for the heave, with the increase of the immersing depth, the motion turns gradually from that the low-frequency motion is dominant into that the wave-

For the large significant wave height, the motion responses of the tunnel element are accordingly large. The peak values of the frequency spectra of the motion responses increase rapidly with the increase of the peak frequency period of waves. Especially, for the heave motion of the tunnel element, the peak frequency of the response spectrum corresponding to the low-frequency motion increases with the increasing peak frequency

The total force of the cables at the offshore side is larger than that of the cables at the onshore side of the tunnel element. Corresponding to the motion responses of the tunnel element, the cable tensions are relatively large and their variations are more complicated in the case as the immersing depth is small and the significant wave height and the peak frequency period are large comparatively. The changing laws of the tunnel element motions

In this chapter, the immersion of the tunnel element is done from the fixed trestle in the experiment, by ignoring the movements of the barges on the water surface. Actually, when the movements of the barges are relatively large, they have influences on the motions of the tunnel element. The influences of the movements of the barges on the tunnel element motions will be considered in the further researches. The numerical investigation will also be carried out on the motion dynamics of the tunnel element in the immersion under

This work was partly supported by the Scientific Research Foundation of Third Institute of Oceanography, SOA (Grant No. 201003), and partly by the National Natural Science

cable tensions are analyzed. Some conclusions are drawn as follows.

and the cable tensions reflect the interrelation of them.

tunnel element motions and the cable tensions.

**4. Conclusions** 

frequency motion is dominant.

irregular wave actions.

**5. Acknowledgment** 

Foundation of China (Grant No. 51009032).

period.


**11** 

Xie Xiaoping

*China* 

*School of Geography and Tourism, Qufu Normal University, Qufu* 

**Formation and Evolution of Wetland and** 

**Multi-Temporal Satellite Images** 

**Landform in the Yangtze River Estuary Over the Past 50 Years Based on Digitized Sea Maps and** 

The Yangtze River originates in the Qinghai-Tibet Plateau and extends more than 6300 km eastward to the East China Sea, a tectonic subsidence belt (Li & Wang, 1991). It is one of the largest rivers in the world, in terms of suspended sediment load, water discharge, length, and drainage area. The Yangtze River Estuary is located in the east China. There are three main islands including Chongming Island, Changxing Island, and Hengsha Island as well as several shoals in the Yangtze River Estuary (Fig. 1). These islands once are shoals emerged from the water and merged to the north bank or coalesced together. In the Yangtze River Estuary, most of the sediments from the drainage basin are suspended. The spatial and temporal variations of the suspended sediment concentration in the estuarine field survey indicate that the sediment is suspended, transported, and deposited under riverine and marine processes, such as river flow, waves, tidal currents, and local topography (Cao et al., 1989; Chen, 2001; Gao, 1998; Li et al., 1995, Huang and Chen, 1995; Xu et al., 2002; Pan and Sun, 1996). In longitudinal section, these islands and shoals stand out on the link between the -10 m isobathic line (the zero elevation means the 1956 Yellow Sea Water Surface in Qingdao Tidal Station, Qingdao, Shandong Province, China) from the upper reach section to the lower reach section, it is a convex geomorphic unit in the Yangtze River Estuary (Fig.2 A-A´ and Fig. 3), in transverse section, these shoals and islands sit in between the channels and distributaries (Fig.2 B-B´ and Fig. 4). In order to analyze the formation and evolution of the wetland and landform of the Yangtze River Estuary, related sea maps from 1945 to 2001 and satellite images from 1975 to 2001 are collected and analyzed. Water and sediment discharge from 1950 to 2003 at the Datong Hydrologic Station 640 km upstream from the estuary mouth are also collected. Datong Hydrologic Station is the most downstream hydrologic station on the free-flowing Yangtze River, where the tidal influence can affect flows hundreds of kilometers upstream. All related sea maps are digitized using Mapinfo7.0, and the sediment volume deposited in this area is calculated from a series of processes dealt in Surfer7.0. The relation between formation and evolution of the wetland and landform of the Yangtze Estuary over the past 50 years were analyzed via Geographical

Information System technology and a Digital Elevation Model.

**1. Introduction** 

*and Engineering)*, Vol. 25, No. 1, (March 2001), pp. 16-20, ISSN 1006-2823 (in Chinese)

Zhao, Z. G. (2007). Discussion on Several Techniques of Immersed Tunnel Construction. *Modern Tunnelling Technology*, Vol. 44, No.4, (August 2007), pp. 5-8, ISSN1009-6582 (in Chinese)
