SEDIMENT DYNAMICS BEHAVIOR AND BEACH PROFILE TYPES BASED ON SEDIMENT PROPERTIES

Sand samples along the shorelines and in the rivers of Tottori Prefecture were assayed for chemical elements using energy dispersive X-ray spectrometer. Samples contained more than 60 wt. % Si, Al, Ca, Fe, Na and Mg less than 10 wt. %. It was found by EOF analysis that Si, Al, Ca and Fe were the significant chemical elements. The spatial variations of first mode of Si are related to sediment dynamic behavior. The transport regime is net accretion when the first mode value of Si is increasing, and net erosion when being decreasing.


INTRODUCTION
Since sandy beaches have been playing an important role in defending the land side area, the importance of coastal conservation has been increasing further.Therefore, field surveys, laboratory experiments and numerical simulations have been carried out to obtain knowledge on beach conservations.Based mainly on these results, beach nourishment and coastal structures have been widely applied.But the sediment management considering river basins has not been done sufficiently.One of the reasons is that it is extremely difficult to evaluate the amount of sediment supplied from rivers, and the mechanism of sediment transport after reaching the coastal areas also not yet been sufficiently made clear.
Field observations using fluorescent sands or colored sands have been carried out to investigate the sediment transport dynamics in the coastal area, but there are problems of selecting sand inputting site and taking out sand particles from the collected sediments.In addition, under the sea weather conditions where the dynamics of sediment transport become active, it will be difficult to carry the filed observation itself in coastal areas.Therefore, focusing on spatial history of the sediment characteristics, analysis of sediment dynamics has been carried out using the physical properties of sediments, the chemical elements and the mineral composition.Measurements of sediment grain size with a sieve or identification of mineral composition using a microscopic requires a great deal time of time and skilled labor.Also in order to shorten time, an expensive laser-type particle diameter measuring device and the X-ray linear chemical element analysis instrument are needed.Against this background, Tsujimoto et al. (2012) calculated the sediment particle size, roundness, sand color and mineral identification from the image obtained using a commercially available scanner, and studying the relationships between the direction of sediment transport and the geology of the river basin.
As a study focusing on chemical elements among sediment properties, Ishiga et al. ( 2010) investigated the geochemical composition of beach sand on the San'in Coast, indicating that SiO 2 has a negative correlation with the sorting coefficient.Terashima et al. (2013) analyzed the sediment grain size and the chemical element concentration changes.For river sediments, the element concentration become high as the grain size decreases, but there is no tendency for K and Ba.It is because that the feldspar of felsic rocks derived from felsic rocks is difficult to refine.
Further as research examples applying the chemical elements in the sediments to the issues of sediment transport, Kumagai et al. (1997) determine the source of sediment transport using the correlation between two samples based on the chemical element ratio.Nagai et al.(2004) are tracking their moving path using the composition ratio of element of the gravels in the offshore area.In addition, Ishii et al. (2011) conducted elemental analysis of bottom sediments at Kujukurihama Beach, and tried to estimate the direction of sediment transport based on the relationships between colored minerals and colorless minerals.
Kato et al, (2013) investigate the beach profiles with the chemical elements in the sediments obtained by X-ray fluorescence analysis method.Okada et al. (2013) classify the mud distribution on the chemical composition of the muds in Tokyo Bay, and estimate the distribution range of the silt component and the sand component supplied from main rivers in Tokyo bay.As shown in F une 5 and 6, 2 near the down hing.We also wing into the co e larger basin a logical Chara In order to inv n river, the ge n using Quant Figure 2         From Fig. 8 and Fig. 10, it can be said that the variation in Si element mode is positive ant the maturity is high on both the Hojo coast and the Uno coast classified as Type B, being negative and low on Mizushiri coast and Hakuto as Type C, and being none and moderate on the Sakyu coast and the Iwato coast as Type A.

CONCLUSION
Correspondence between the elements presumed from the geology of the river basin and the sampled sedimentary element is good.It was confirmed that Si, Fe Al and Ca are important elements as chemical elements, and their variations correspond to changes in particle size and mineral composition.The variation of Si element mode and the sediment dynamic behaviors are related, the variation of Si element mode increases in the deposition type, and decreases in the case of the erosion type.These relationships focused on Si element are shown in Table 1.
Figure 3 show ribution ratios ending on the nged from har change from s a River with l he Tottori coas Figure 7 ws the distribu s from the To m the Hamamu asing from the he fact that f Si 2 O 8 ), Plag the sediment w Figure 9 etween chemi Figure 10 obtained.The sediment dynamic behavior between Mizushiri coast and Hakuto coast corresponds to type C. Furthermore, the sediment dynamic behavior between the Sakyu coast and the Iwato coast correspond to type A. As a factor causing the different sediment dynamic behavior, the sediment transport in the east-west direction due to seasonal variation is considered.Kawauchi et al. (2010) have conducted a total of four field surveys on the Tottori Sand Dune coast located on the east side of the Sendai rives in winter 2000 to 2005 and May 2009, and as a result, the same results as this research are obtained.

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