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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 shoreline 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. 相似文献
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Balaena Bay, Wellington Harbour, New Zealand, has a small pocket beach that was covered originally by pebbles and cobbles. In February and October 1982, the beach was nourished with sandy granular gravel, the stability of which was monitored until February 1984. Although isolated from oceanic swell, the new beach readily responded to locally generated wind waves which induced both northwards and southwards longshore drift. The net effect was erosion of the southern beach, aggradation over the central beach, and minor fluctuations at the northern end. Yet despite this mobility nearly all the nourishment sediment was retained in the littoral zone. Beach volumes, calculated for each survey, varied little and sediment distribution patterns revealed negligable transport of nourishment sediment to adjacent beaches and offshore areas. Stability is further confirmed by compositional data which record no preferential loss of the sandstone, argillite, and quartz components. The only compositional changes were the incorporation into the new beach of small (< 10%) quantities of sediment derived from the old beach surface and from biogenic productivity. 相似文献
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Chirananda De 《Marine Georesources & Geotechnology》2013,31(2):79-95
Formation of burrow-head mud volcanoes by the mud-loving amphibious crab Uca marionis (Alcock) selectively on the either sides of estuary mouths along the Bay of Bengal coast, eastern India, requires peculiar substratal and biological conditions where soft muddy bottom sediments of the coastal mudflats are covered by a thin blanket of relatively rigid beach sands that provide a false substrate stability. Shallow-seated mud layers, being within the substrate penetration power, allow opportunistic burrowing by the crab and consequent oozing out of internal mud slur to form conical heaps of mud resembling volcanic cones. Removal of this thin sand cover prompts very fast erosion of the bottom mud and consequent widening of the estuary mouth and rapid beach erosion. A thick and rigid sand cover restricts deeper burrowing by the crabs. Uca marionis mud volcanoes, by virtue of limited power of vertical penetration down to required muddy substrate and requirement of special substrate conditions and geomorphic position along the coastal zone, are considered as unique ichnological tools that readily identify and precisely demarcate highly unstable or erosion-prone beach sectors, and thus help in planning, protection and execution of various coastal developmental programs. Wide zoogeographic distribution of Uca in tropical-subtropical sea coasts greatly enhances the application potential of this new ichnological tool. Fossilized biogenic mud volcanoes in post-Jurassic geologic records would ease taxonomic identification of the ancient trace producers and coastal marine palaeogeomorphic interpretations. 相似文献
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