The Sedimentary Source, Planform Stability and Shore Normal
Total Page：16
File Type：pdf, Size：1020Kb
Acta Oceanol. Sin., 2015, Vol. 34, No. 3, P. 76–89 DOI: 10.1007/s13131-015-0635-6 http://www.hyxb.org.cn E-mail: [email protected] The sedimentary source, planform stability and shore normal morphological change of the Xichong beach on the southern coast of the Dapeng Peninsula of Shenzhen, Guangdong Province, China ZHANG Song1, WANG Wei2*, HUANG Rihui2, XU Liubing2 1 Shenzhen Dapeng Peninsula National Geopark Administration Office, Shenzhen 518121, China; 2 Geographic School, South China Normal University, Guangzhou 510631, China Received 22 February 2014; accepted 5 August 2014 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2015 Abstract The coast of the Dapeng Peninsula has been honored as one of “the eight most beautiful coasts in China”. The most precious tourism resource for the peninsula is headland bay beaches, among which the beach at Xichong on the southern coast of the peninsula is the longest and the most important one. The information of the stability, sedimentary source and shape change of the beach is very important for maintaining the beach in terms of sustainable development of the peninsula. Heavy minerals in the sand of the beach and the inland stream at Xichong are compared with those of a nearby beach on the same coast to determine the beach sand source; with help of a computer software, MEPBAY, the equilibrium planforms of the beaches on the peninsula are compared with those of an island without rivers to evaluate the stream's effects on the beach stability; cross shore profiles along the Xichong beach are also surveyed in different seasons of a year to assess the annual shore normal beach changes affected by the stream input, and the relation between the equilibrium planform state and cross shore changes of the beach. It is shown that (1) stream is the main sedimentary source of the beach and the weathering materials of the rocky headlands on both sides of the bay transported by waves are the second source for the beach but it is limited, sand from an inner shelf is not the sedimentary source for the beach at present and was not even during the Holocene transgression; (2) the Xichong beach cannot reach static equilibrium around the entire bay shoreline, the segment of the shore- line where a stream outlet is located is in dynamic equilibrium, and the unstable section occurs in the wave shadow region in the lee of an offshore island; (3) no matter whether the section of the beach shoreline at Xichong is in an equilibrium state or not, it is eroded in the typhoon season and recovered after the season, the maximum change in erosion and accretion occurs in the unstable segment; (4) the Xichong beach can only have small sand body since it is supplied with sand mainly form inland streams, resulting in a possible danger in which sand loss induced by human activities or huge storms cannot be replenished naturally. Key words: headland bay beach, sedimentary source, beach stability, beach seasonal change, Dapeng Peninsula Citation: Zhang Song, Wang Wei, Huang Rihui, Xu Liubing. 2015. The sedimentary source, planform stability and shore normal morphological change of the Xichong beach on the southern coast of the Dapeng Peninsula of Shenzhen, Guangdong Province, China. Acta Oceanologica Sinica, 34(3): 00–00, doi: 10.1007/s13131-015-0635-6 1 Introduction trend of erosion to sandy beaches on a worldwide scale induced A sandy shoreline bounded by rocky outcrops or natural or by the global warming and sea level rising (IPCC, 1996), the fo- man-made headlands, where its shoreline assumes some form cus of coastal research has shifted from straight coasts to curved of curvature, is defined as a headland bay beach (Short and beaches (Hsu et al., 2010). The headland bay beaches have been Masselink, 1999; Klein, 2004). Headland bay beaches represent received more and more consideration in recent years in China about 50% of the world coastline (Inman and Nordstrom, 1971; (Yang and Zhang, 2007; Lee et al., 2007; Dai et al., 2010; Kuang et Short and Masselink, 1999) and occupied over 20% of the coasts al., 2010; Zhuang et al., 2009; Yu and Chen, 2011; Li et al., 2012). of southern China (Dai et al., 2010). The sand movement of a The headland bay beaches are always presented as bay bar- headland bay beach is restricted by the headlands and the equi- riers formed between two adjacent headlands with lagoons be- librium planform of the beach is the response to a prevailing hind on the coasts of South China (Li et al., 1986; Chen, 1995, swell direction and sediment inputs. When the headland bay 1996; Dai and Li, 2004; Dai et al., 2007). They may have many beach is in a state of static equilibrium, the predominant waves potential possible sedimentary sources including deposits on are breaking simultaneously around the whole bay periphery the continental shelf, detritus form inland streams and mate- and a littoral drift is almost non existent (Silvester and Hsu, rials eroded by waves from coastal headland rocks of the bay 1993; Hsu et al., 2000; Hsu et al., 2010). Owing to a continuing (Wang, 1985; Li, 1986; Li et al., 1986; Wang, 2000). Studies shows Foundation item: Shenzhen Dapeng Peninsula National Geopark Project of China under contract No. 340775; the Natural Science Foundation of Guangdong Province of China unde contract No. S2012010008610; the National Natural Science Foundation of China under contract No. 40871020. *Corresponding author, E-mail: [email protected] ZHANG Song et al. Acta Oceanol. Sin., 2015, Vol. 34, No. 3, P. 76–89 77 that most of the bay barriers located on the coast of non estuary future. The information of the stability, sedimentary source and areas in South China mainland are composed of mud and sand morphological change of the Xichong beach is very important which were derived from inner shelf along with sea level rise for maintaining the beach in terms of sustainable development in Holocene time (Li, 1986; Li et al., 1986). However, the sed- and may be typical of many other beaches of the peninsula. The imentary source for the bay barriers developed on the coasts sedimentary source and the morphodynamic changes includ- of the islands off South China mainland, such as the islands of ing the planform and the shore normal shape changes of the Hong Kong area, merely comes from inland streams and seems Xichong beach are investigated in this study. to have no relationship with the inner shelf sand bed during the Holocene period due to the hilly and deeply indented coastline 2 Geographic and geologic setting of Dapeng Peninsula of the islands (Wang, 2000). The Dapeng Peninsula is half main- land and half island because it is a tectonic uplift block (Huang 2.1 Geographic setting et al., 1983) sticking out from the mainland of South China and The Dapeng Peninsula is located on the coast of southern being almost completely surrounded by the sea with a steep China projecting into the South China Sea between the Dapeng subaqueous shore slope. There is considerably less under- Bay and the Daya Bay on its eastern and western sides, respec- standing whether the sedimentary source for the bay barriers tively (Fig. 1). The Qiniang Mountain, which is a dead volcano developed on the peninsulas of South China, like the Dapeng with a height of 869.7 m above sea level, is the highest peak of the Peninsula, is from the inner shelf or from the inland streams. peninsula. The Xichong Bay is situated on the southern (south- Furthermore, there are only a few reports about the relation eastern) margin of the peninsula facing the South China Sea and between equilibrium states and sediment supplies as well as is characterized by embracing a barrier sand beach with rocky shore normal shape changes of the headland bay beaches on headlands on both sides (Fig. 1). The Xichong beach is about 3 the coast of South China. km long with three inland streams, the Nanmenchong River at The coast of the Dapeng Peninsula has been honored as one the eastern end, the Danshuichong River in the middle and the of “the eight most beautiful coasts in China” by Chinese National Xichong River at the western end of the bay, flowing across the Geography Magazine (Chinese National Geography, 2005). One beach to the sea (Fig. 1). Before running across the beach, the of the main coastal types on the peninsula is the bay barriers or water of the Danshuichong River and the Xichong River pours the headland bay beaches which are the most precious tourism into two modern lagoons respectively which are located imme- resource for the peninsula as well (Zhang et al., 2013). The Xi- diately behind the middle and western parts of the barrier. The chong beach on the southern coast of the Dapeng Peninsula is Dongchong Bay is located next to the Xichong Bay on the same not only the longest but also the most important headland bay coast and the distance between them is no more than 3 km. The beach of the peninsula. In the year of 2012, 2.931×106 tourists Dongchong Bay is also a headland bay embracing a barrier with traveled to the peninsula and almost the half (1.45×106) of them a lagoon behind (Fig. 1). The length of the barrier beach is less visited the Xichong beach (Zeng, 2013). Given the rising pres- than 1 km. An inland stream, the Dongchong River, flows into sure from the development of coastal tourism on the peninsula, the lagoon and the outlet of the stream is located at the western the Xichong beach can be expected to play an increasingly im- end of the barrier (Fig.