Numerical Research On Evolvement Character Of Submarine Sand Waves In The Northern South China Sea

The geological structure, submarine landforms and hydrodynamic conditions ofthe South China Sea are very complicated. There are a large number of submarinesand waves in this area, which is one of the serious threats to the submarineengineering facilities. The sand waves are active in most cases. Sand waves willmigrate rapidly under the influence of tide wave, storm surge, internal waves, and soon. The migration of sand waves might cause a serious of significant damage, forexample, free span of submarine pipelines, or even the breakage of the pipelines, thecollapse of the rig platform, the sedimentation of the waterway and the breakage ofsubmarine cable and so on. Some scholars have been studied the sand waves in thisarea, however, some scientific problems need to be further studied.Based on the existing research on submarine sand waves in the South China Sea,the evolvement of the submarine sand waves in the focus areas is studied, the surfacesediments and sand wave’s character are summarized and analyzed, the bottom flowfield data between2010and2011in the study area is simulated by the ROMS model,the incipient velocity of surface sediment in specific position is calculated; themigration of sand waves is simulated and calculated by using Rubin’s and Shinohara’sformula; combining with typhoon data and bottom flow field data, the response of thesand waves under the influence of typhoon is analyzed. Main results were shown asfollows:The surface sediments in the sand wave area Ⅰand Ⅱ can be divided into fourtypes, including sandy gravel, gravely sand; gravely muddy sand, and sand withgravel. The median diameter in the study area is between0.233mm and2.234mmwith the mean value1.414mm. Sand waves in the study area are mostly ripples withstraight crest line, and the strike of the crest line is NE-SW, the lee slopes have two different trends, which are NW and SE respectively. Sand waves with wave heightlower than0.5m are widely distributed, with the highest5.67m. Sand waves in thestudy area migrated from northwest to southeast between2010and2011.The results of the migration direction calculated by Rubin’s formula combiningwith bottom flow are very similar with collected datum. The migration distance ofdifferent position is between0m and21.8m. The numerical results of migrationdistance of some station is0.25m by using Shinohara’s formula, which is significantlysmaller compared with the1.9m calculated by Rubin’s formula.The super typhoon “FANAPI” enhanced the bottom flow velocity in theresearched area significantly. The migration distance of2sites in the study area is2.0m and2.9m during “FANAPI”, with a percent of9.17%and26.36%in its annualmigration distance, which proves that the typhoon makes a significant impact onsubmarine sand waves.