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Simulation of Tidal Flat Sedimentation in Response to Typhoon-induced Storm Surges: A case study from Rudong Coast,Jiangsu,China
Pages: 79-90
Year: Issue:  1
Journal: Acta Sedimentologica Sinica

Keyword:  tidal flat sedimentationspatial variabilitycross-shore profile morphologystorm surgesdynamic simulationJiangsu coast;
Abstract: Tidal flat sedimentation is mainly controlled by sediment supply and hydrodynamic conditions,and the resultant sedimentary records are valuable in the study of the evolution of coastal environments at various time-scales ranging from several days associated with extreme events to millenniums related to climate changes. A strong storm surge event may destroy a relatively thick sedimentary sequences formed over a long period of time. Therefore,it is important to evaluate the influence of extreme events on the continuity and temporal resolution of tidal flat sedimentary records. In the present contribution,an approach to the modeling of the spatial distribution patterns of tidal flat accretion / erosion,under both fair weather and storm surge conditions,is proposed. This model is applied to the Rudong coast,Jiangsu Province,which is exposed to frequent typhoon attack,to illustrate the sediment dynamic processes and the modification of normal tidally-dominated sedimentary sequences associated with storm surges. The model consists of four parts that deal with the current velocity and near-bed shear stress due to tides or combined tide-typhoon effects,suspended sediment transport and vertical( settling and erosion) fluxes,bedload transport and accretion / erosion,and morphological evolution of the bed,respectively. Driven by the tidal water level curve reconstructed by using the harmonic analysis of the observed data from the study area,the model output reproduced the zonation pattern of intertidal flat sedimentation under the fair weather conditions. Furthermore,its prediction about the tidal flat cross-shore profile associated with a small bed slope,strong tidal currents and a weak time-velocity asymmetry,which is characterized by a "double convexity"shape,is consistent with the observed shape for the study area. According to the model output,the two convexities are located in the vicinity of mean high water and mean low water,respectively. Subsequently,the model was run taking into account both tides and storm surges. Under the condition that a storm surge occurs in association with astronomical spring tides,which occurred over the study area in 1981( i. e.,Typhoon No. 8114),the model prediction is that the bed is subjected to mud accretion over the supratidal zone and the upper part of the intertidal zone,while sand erosion occurs over the lower-middle parts of the intertidal zone. Thus,an erosion surface is formed within the sedimentary sequence,representing the storm effect. This pattern,once again,is consistent with the in-situ observation made following the typhoon event for the area. The model output implies that storm-induced sedimentary record can be found in the upper parts of the tidal flat. It should be noted that the results presented here are only preliminary: a number of detailed morphological parameters about the storm deposit are not available in the model output. In the future,the model may be further improved by taking into account the factors such as the boundary characteristics under extreme shallow water conditions,variability of grain size distribution curves,combined tidal currents and waves,biological activities,tidal creek migration and artificial land reclamation. In combination with inverse methods,the forward modeling will be beneficial to a better interpretation of the formation of tidal flat sedimentary records.
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