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Masayasu IRIE, Yuji FUJII, Teruhisa OKADA, Shuzo NISHIDA
2013 Volume 69 Issue 2 Pages
I_501-I_505
Published: 2013
Released on J-STAGE: November 12, 2013
JOURNAL
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Surface current data measured by HF oceanic radar is assimilated with Regional Ocean Modeling System (ROMS) and four dimensional variational method (4D-Var). Sensitivity analyses are carried out to decide appropriate parameters for the data assimilation. 4D-Var reduces RMSE of surface velocity by 0.05 m/s at maximum. 4D-Var with the Inner-loop of 10, the radius of horizontal error covariance of 1km gets the better RMSE than other cases. The assimilated surface currents are compared with those assimilated with nudging method. While the results of nudging assimilation have discontinuous change of the currents, those of 4D-Var do not and the time series of surface velocity come closer to those of the observations than those assimilated with nudging outside of the observation range.
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Masayasu IRIE, Teruhisa OKADA, Shuzo NISHIDA
2013 Volume 69 Issue 2 Pages
I_506-I_510
Published: 2013
Released on J-STAGE: November 12, 2013
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Four dimensional variational (4D-Var) data assimilation is carried out using Regional Ocean Modeling System (ROMS) and the vertical current profiles which are measured by Osaka Bay Water Quality Observation System in this paper. The applicability of 4D-Var is tested through the sensitivity analyses in which parameters for 4D-Var and sets of control variables are changed. The RMSE of velocity at the observation stations decreases more with the number of inner-loop of 10, the radii of horizontal and vertical error covariance of 5 km and 3m respectively. The effect of the 4D-Var appears in the analyses of velocity near the surface at some stations where there is larger difference from the observations and those of surface salinity even though salinity is not assimilated directly.
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Yusuke TANAKA, Nobuhito MORI, Junichi NINOMIYA, Koichi SUGIMATSU, Hiro ...
2013 Volume 69 Issue 2 Pages
I_511-I_515
Published: 2013
Released on J-STAGE: November 12, 2013
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Seto Inland Sea is the largest semi-enclosed sea in Japan. The operational numerical hindcasts have been conducted by Fishery Research Agency since 2006 by POM oriented FRA-JCOPE model. Since the development of POM, the numerical model and scheme of ocean models have been developed in the last decade. Specially the modeling in strong mixing condition has been improved. This study applied ROMS both annual ocean climate hindcasts and short-term impact due to typhoon in the Seto Inland Sea. The numerical results are compared with ROMS and FRA-POM model and the difference of results is discussed in detail.
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Soo Youl KIM, Tomonori MATSUURA, Yoshiharu MATSUMI, Kazuhisa TAMAI, To ...
2013 Volume 69 Issue 2 Pages
I_516-I_520
Published: 2013
Released on J-STAGE: November 12, 2013
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This paper describes the performance of the weather research and forecasting (WRF) model applied for Typhoon Maemi in 2003 in the mid-latitude (N35°_55°) using grid point value (GPV) data of NCEP FNL (ds083.2) and NCEP/NCAR Reanalysis (ds090.0), by changing planetary boundary layer scheme and cloud microphysics. It was found that typhoon tracks are closer to the best track when using ds090.0 data, while intensity is well simulated by using ds083.2 in the range of over N30°. In addition, wind is more sensitive to the planetary boundary layer scheme than the cloud microphysics. Sea level pressure is similarly sensitive to both schemes of the planetary boundary layer scheme and the cloud microphysics.
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Yusuke UCHIYAMA, Dai MIYAZAKI, Hideki KAIDA
2013 Volume 69 Issue 2 Pages
I_521-I_525
Published: 2013
Released on J-STAGE: November 12, 2013
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Current effect on waves (CEW) is examined for formation of rip channel systems with a barotropic model that consists of an Eulerian phase-averaged shallow water equation with a vortex-force formalism, WKB ray equations, and a bed evolution equation with the Soulsby-Van Rijn's total sediment flux formula. CEW acts on reducing the offshore extent of seaward rip currents through wave refraction on the currents, leading to modifying the budget of sediment flux and the associated surf-zone topography. Inclusion of CEW results in shoaling rip channels, deepening offshore mounds, and elongating alongshore spacing of rip channels with both the normal and oblique incidence of offshore waves.
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Masatoshi ENDO, Akio KOBAYASHI, Takaaki UDA, Masumi SERIZAWA
2013 Volume 69 Issue 2 Pages
I_526-I_530
Published: 2013
Released on J-STAGE: November 12, 2013
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A new model for predicting beach changes was developed using the cellular automaton method, independently taking sand transport under ongoing and outgoing waves into account, while retuning the fundamental concept of the BG model. The model was used to predict beach changes around a detached breakwater and a groin with a lower crown height built on the Osawa coast in Chiba Prefecture. The observed changes were well reproduced, and the applicability of the model to the prediction of beach changes with complicated structural conditions was confirmed.
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Takaaki UDA, Yasuhito NOSHI, Takayuki KUMADA, Hiroshi MIZUGAKI, Ko-ich ...
2013 Volume 69 Issue 2 Pages
I_531-I_535
Published: 2013
Released on J-STAGE: November 12, 2013
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On northern Kujukuri Beach extending between Iioka and Katakai fishing ports, beach has been eroded due to the decrease in sediment supply from Byobugaura sea cliff, which was triggered by the installation of concrete blocks along the sea cliff as a measure against cliff erosion by the 1970s. These beach changes were reproduced using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept) proposed by Serizawa et al. (2006). Also future beach changes were predicted using the same model. It was concluded that some measures are required to preserve sandy beach of Kujukuri Beach.
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Koichi HOSAKA, Sadakazu KATORI, Yoshihiro NISHIUKE, Susumu KUBOTA
2013 Volume 69 Issue 2 Pages
I_536-I_540
Published: 2013
Released on J-STAGE: November 12, 2013
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In order to determine the distance required over a sand bed for the transport rate by wind to be in equilibrium, and the distance from the end of the sand bed over which most of the falling sand grains will deposit, laboratory experiments were carried out in a large blow-off type wind-tunnel under the realistic conditions. Thus, results from the measured vertical distributions of wind-blown sand transport rates suggested that: (1) the equilibrium distance was 8-10m for the fine sand and 15m for the coarse sand; (2) the erosion area which appeared in the beginning of the sand bed was 6m long for a fine sand bed and 8m long for a coarse sand bed; and (3) the leeward distance from the end of the sand bed to a point that most of the sand grains could not pass was 4m for the case of fine sand and 6-8m for the case of coarse sand.
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Masayuki BANNO, Yoshiaki KURIYAMA
2013 Volume 69 Issue 2 Pages
I_541-I_545
Published: 2013
Released on J-STAGE: November 12, 2013
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This study developed the shoreline change model using a random effect of time heterogeneity which was caused by the influence of unmeasured variables, and the model could estimate the effects of the wave energy and the tidal level. The developed model predicted the future shoreline positions from 2008 to 2095 with assumptions of sea level rises and wave climate changes under the global climate changes on the Hasaki coast in Japan, facing the Pacific Ocean. The simulation results showed that the foreshore would be eroded approximately 20 m and the shoreline position would retreat approximately 40 m due to global climate change by the end of this century.
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Lulu HE, Masashi OKAJIMA, Wataru KIOKA, Toshikazu KITANO
2013 Volume 69 Issue 2 Pages
I_546-I_550
Published: 2013
Released on J-STAGE: November 12, 2013
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The three-dimensional lattice Boltzmann method (LBM) is used to simulate the behavior of bed-load layer in open channel shear flow. The 3D LBM for particle-fluid suspensions originally developed by Ladd (1994) has been extended to free-surface flow and to higher Reynolds number regime. The SGS turbulence term based on Smagorinsky model is also included in the LBM flow simulation. The present simulation predicts well the behavior of each particle in the bed-load layer both in saltation and sheetflow regimes. Results of the present simulation for the height and length of saltation,the bed-load velocity and the existing probability density agree fairly well with the experimental data from Gotoh et al. (1994).
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Shin-ichi YANAGISHIMA
2013 Volume 69 Issue 2 Pages
I_551-I_555
Published: 2013
Released on J-STAGE: November 12, 2013
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Based on the observed data for 27 years from 1986 at Hazaki Oceanographical Research Station, the changes of cross-shore profile and the mean sediment diameter at beach surface by huge storms have been extracted. As results, the longshore bar disappears by storm and high waves come to reach the shore. Therefore, the newly formed bar comes to be eroded easily and fine sand cannot stay near the shoreline. On the assumption that the storm is made huge by global warming, it is expected that the former beach slope becomes steep and the grain diameter near the shoreline roughens.
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Eiji HARADA, Hitoshi GOTOH, Naoki TSURUTA
2013 Volume 69 Issue 2 Pages
I_556-I_560
Published: 2013
Released on J-STAGE: November 12, 2013
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The components of shear stress in the oscillatory sheet-flow layer, especially concerning the inter-granular stress, are considerably unknown field because of difficulty in experimental measurements. In the present study, components of the shear stress in the oscillatory sheet-flow layer have been addressed by the LES for the particulate flow based on the Euler-Lagrange coupling. The inter-granular stress has been calculated from the solid-liquid interaction term. Then the vertical profile of each component of the shear stress has been shown in some phases. Furthermore, the predominant region for collision and contact has been found by considering both the particle concentration related to the interstitial area between particles and the turbulence intensity for particle velocity.
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Fumihiko YAMADA, Seiya SUENAGA, Gozo TUJIMOTO, Hajime SHIROUZU, Sota N ...
2013 Volume 69 Issue 2 Pages
I_561-I_565
Published: 2013
Released on J-STAGE: November 12, 2013
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A medical X-ray computed tomography (CT) scanner was applied to dynamic measurements of beach profile changes, internal sediment structures, and sediment transport processes during wave actions in the laboratory experiments. An acrylic flume 7 m long and with an inner rectangular cross-section of 0.3 m × 0.3 m passes through the mobile gantry of a medical X-ray CT-scanner. Reconstructing three-dimensional images using Hounsfield Units (HU), the relationships between beach profile changes and sediment density distributions within the depth of disturbance (DOD) are examined. The DOD is located within 9 mm below the bottom surface and sixty times larger than mean sand diameter (d50). A negative correlation is found to be existed between them.
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Yosuke NAGASAKA, Shinji SATO
2013 Volume 69 Issue 2 Pages
I_566-I_570
Published: 2013
Released on J-STAGE: November 12, 2013
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The field survey of the 2011 Tohoku Tsunami in Unosumai District of Kamaishi City, Iwate Prefecture suggested the collapse of embankment due to momentary liquefaction. We performed numerical simulation of the effect of pore pressure variation on the stability of embankment. A consolidation model considering saturation of the soil was applied. The numerical analysis demonstrated that the embankment with lower saturation can be unstabilized by the rapid drawdown due to tsunami. Laboratory experiment in the oscillatory flow tunnel also verified that unsaturated sand bed becomes unstable by the rapid decrease in pressure and thus significantly increases the sand transport rate.
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Yasuyuki NAKAGAWA, Kazuo NADAOKA, Hiroshi YAGI, Yasuo NIHEI, Akihiro K ...
2013 Volume 69 Issue 2 Pages
I_571-I_575
Published: 2013
Released on J-STAGE: November 12, 2013
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Very soft mud with high water content of over 400 % is prevailing in the deeper area off Haneda in the Tokyo Bay and behavior of the mud is crucial for the water environment around the area. The fine sediment transport processes of such muddy sediments were modeled considering the sedimentary characteristics such as vertical profiles of mud concentration near the bottom surface. Assuming the near surface muddy sediment as Bingham fluid, analytical solution for horizontal mass flux of the mud layer was newly derived. The equation was also applied to estimate the sediment transport during the observed typhoon event in the Tokyo Bay with a 3-D circulation model (POM) and wind wave model (SWAN). The results showed applicability of the model to simulate the muddy sediment transport process during the storm event.
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Shigeru KATO, Takumi OKABE, Hidenori MITSUYAMA, So NAKAGAKI
2013 Volume 69 Issue 2 Pages
I_576-I_580
Published: 2013
Released on J-STAGE: November 12, 2013
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The experiment of color sand tracking was carried out to investigate sediment movement on a tidal flat. Observations of current and water level were also conducted in two days. Longshore currents on the flat were much influenced by wind and cross-shore currents responded to the tidal oscillation. By the experiment, the sand was moved to the north widely by strong southerly or westerly winds in a short time and the sand was also pushed southward by frequent and relatively mild wind from the north. The contents of chemical elements in the sands were measured by the X-ray Fluorescence analysis. The distribution of the contents of some single elements and correlation among datasets of element contents indicated the similar pattern of sand movement by the experiment.
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Akiyoshi KATANO, Nobuyuki KURUSHIMA, Sakae NAGAI, Hiroshi IZUMIDA, Tos ...
2013 Volume 69 Issue 2 Pages
I_581-I_585
Published: 2013
Released on J-STAGE: November 12, 2013
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Scour formation behind submerged breakwaters is seen in two coasts with different characteristics, which shows the relation between scour formation and submerged breakwaters. In this study, mechanism of the scour formation has been examined by comparing the characteristics of the two coasts. Some evidence of the relation between the scour formation and turbulence behind submerged breakwaters were found and simultaneous observation of current, turbidity, and seabed change were carried out in the area behind the submerged breakwater. The observation results indicate that the turbulence due to wave breaking on the submerged breakwaters and offshore mean current strongly affect the sand transport behind the submerged breakwaters.
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Thi Lan Huong VU, Norimi MIZUTANI
2013 Volume 69 Issue 2 Pages
I_586-I_590
Published: 2013
Released on J-STAGE: November 12, 2013
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Image analysis using Web camera can be very useful tool to clarify the mechanics of beach deformation because it allows time domain analysis of shoreline changes. The purpose of the present study is to extract shoreline from the video images using image processing and investigate the relationship between shoreline change and waves. New method to detect shoreline in images has been proposed and it has been demonstrated to detect shoreline more stable than the exiting CCD model. Results reveal that the shoreline tends to forward if the significant wave height is ranged between 1m and 2m, whereas it tends to retreat if the significant wave height is larger than 3m. Furthermore, the image analysis reveals that presence of artificial reefs reduces the retreat of shoreline during storm
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Takashi YAMANO, Ryuichi FUJIWARA, Kouji NOMURA, Kouichi SHIRAKI
2013 Volume 69 Issue 2 Pages
I_591-I_595
Published: 2013
Released on J-STAGE: November 12, 2013
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In this study, about the characteristics scour of the pile-supported wave absorbing breakwater with a low crown height with different pile spacing and effects of the countermeasure against local scour, we intended to grasp by moving bed tests with plane water tank. As a result, we found that the scour depth is reduced by widening the spacing pile. Also we confirmed the effect of the countermeasure against local scour by model tests and field observation. In addition, by organizing the pile diameter including the countermeasure against local scour, there is a possibility that can be evaluated as a single pile. In addition, detailed studies are needed in the future as the effects of pile group.
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Takaaki UDA, Shinji SATO, Kenji NOGUCHI, Makoto SHIBASAKI, Takayuki KU ...
2013 Volume 69 Issue 2 Pages
I_596-I_600
Published: 2013
Released on J-STAGE: November 12, 2013
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Wave flume tests and movable-bed experiments were carried out to improve wave dissipation effect of an artificial reef with crests and to reduce strong shoreward currents on the reef. Not only the effect of an ordinary-type artificial reef with crests but also that of a tandem-type artificial reef were investigated. It was found that the effect of an artificial reef with three crests was better than those of the other types in terms of the stabilization of the beach shoreward of the artificial reef.
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Masataka HORIIKE, Masataka YAMAGUCHI, Hideto EGUCHI, Akihiko YAHIRO, Y ...
2013 Volume 69 Issue 2 Pages
I_601-I_605
Published: 2013
Released on J-STAGE: November 12, 2013
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At harbor entrance in Tagonoura Port, channel infilling has continuously occurred so far, and the maintenance dredging has been usually carried out. In order to reduce the infilling rate, implementation of spot dredging has been proposed and the field experiment has been carried out since August, 2012. This study intends to clarify the mechanism of channel infilling and effectiveness of the spot dredging works. By analyzing the bathymetric survey data and wave observation data, the effectiveness of spot dredging works were confirmed. Numerical model experiments have been also conducted to examine effective arrangement of the spot dredging.
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Shin-ichi TABATA, Tsutomu KAWAGUCHI, Yoshinori YAMAKAMI, Hiroshi SAKUR ...
2013 Volume 69 Issue 2 Pages
I_606-I_610
Published: 2013
Released on J-STAGE: November 12, 2013
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In Bakkai Fishing Port where the sand drift phenomenon has been occurring, the burial of the port and the channel is longstanding problem. Generally, a sand drift simulation at a coastal area where tidal fluctuation is small, only wave-induced currents are considered. However, at this area, waves are interrupted by Islands and merely weak currents are generated. On the other hand, this area is high wind site, so there is a possibility that the currents due to wind influence the flow environment. In this paper, (1) we figured out the sand movement and its generation mechanism from observation data and flow property. (2) We proposed the new method of estimating the currents due to wind in the long-time projection of geographical change, and confirmed the improvements of degree of projection reproducibility.
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Yuta MITOBE, Hoang Cong VO, Mohammad Bagus ADITYAWAN, Hitoshi TANAKA
2013 Volume 69 Issue 2 Pages
I_611-I_615
Published: 2013
Released on J-STAGE: November 12, 2013
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Characteristics of the beach recovery process on Sendai Coast after the 2011 Great East Japan Earthquake Tsunami are discussed through the analysis of shoreline changes measured from aerial photographs which have been taken every 1 or 2 months. Coastal structures located near shoreline such as detached breakwaters, which reduce long-shore sand transport, have a significant effect on the recovery process. An embankment of 15m height located near the Nanakita River mouth has been eroded intermittently by high waves to be a large source of sand. The retreat of the shoreline near the Nanakita River mouth has been reduced by 12 cm/day on average, while the change rate near the Natori River mouth is 7 cm/day. The beach morphology on Sendai Coast is not in an equilibrium state even after 2 years from the tsunami.
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Hitoshi TANAKA, Mohammad Bagus ADITYAWAN, Min ROH, Hoang Cong VO
2013 Volume 69 Issue 2 Pages
I_616-I_620
Published: 2013
Released on J-STAGE: November 12, 2013
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The Great East Japan Tsunami of 2011 caused severe morphology changes along the affected shoreline, including sand formation in front of the river mouth. This study investigates the recovery process of this sand formation at several rivers. Sand spit intrusion into the rivers occurs during the recovery process. The river mouth width and the intrusion distance show similar relation and trends, which was also observed in sand intrusion into the river due to jetty construction. A more detail analysis show that the river mouth was severely eroded by the tsunami. The water depth in the river mouths was significantly deeper after the tsunami. Thus, the location of the depth of closure was moved into the rivers, which lead to the sand intrusion. This agrees well with laboratory experiments from previous study.
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Nobuyuki ONO, Keiji KUROKI, Kenji ISHIMOTO, Yoshimasa ITO
2013 Volume 69 Issue 2 Pages
I_621-I_625
Published: 2013
Released on J-STAGE: November 12, 2013
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Masuda port is located in both sides of the mouth of Takatsu River, the access channel of which passes behind a river-mouth bar. This study intends to develop a tool for examination of countermeasures against channel infilling which is very linked with deformation of river-mouth bar. First, the relation between the sand bar deformation and channel infilling has been examined for the river mouth area of Takatsu River through analysis of aerial photos, current and wave data, bathymetric survey data, and so on. As the results, two dominant processes of flushing sand bar due to flood and reformation of sand bar by waves are confirmed. Also, numerical simulations for the two dominant processes have been conducted and the reproducibility of the model has been examined.
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Kohji UNO, Hiroaki NAKANISHI, Gozo TSUJIMOTO, Tetsuya KAKINOKI
2013 Volume 69 Issue 2 Pages
I_626-I_630
Published: 2013
Released on J-STAGE: November 12, 2013
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In this study, to clarify the forces affecting on the temporal-spatial variation of the median grain size and topographic change of the sand gravel beach, field observations were carried out for 3 years and a numerical model was developed. Study site is the east coast beach in the Narugashima Island located between inner bay - Osaka bay - and open sea - Kii channel -, in Seto Inland Sea, western Japan. From the result of field observations, the periodic disturbance in this beach was confirmed. It tends to be coarse at the first half of observation period and be fine at the second half of observation period. On the other hand, the result of numerical simulation shows that the blown sand is important factor affecting on the temporal-spatial distributions of the median grain size and topographic change in this beach.
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Manu LUSIA, Hiroki SHIRAISHI, Masakazu ITO, Takaomi HOKAMURA, Sota NAK ...
2013 Volume 69 Issue 2 Pages
I_631-I_635
Published: 2013
Released on J-STAGE: November 12, 2013
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The geomorphological response of intertidal flats adjacent to Shirakawa River mouth due to flush flood torrential rainfalls on July 12, 2012 was examined using field observation data. Mudflat profiles have been measured monthly along six cross-shore lines exceeding 1,000 m since 2006. Because all the measured profiles were approximated by a quadratic profile represented by the three parameters based on the results of Yamada and Kobayashi (2003), a vertical displacement parameter was used to understand the temporal variations of measured profiles. The maximum average accretion along the measured profiles due to this flooding was found to be 30cm and three times larger than those of past 8-years data.
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Yusuke TAGUCHI, Yoshimitsu TAJIMA, Mohammad Asad HUSSAIN
2013 Volume 69 Issue 2 Pages
I_636-I_640
Published: 2013
Released on J-STAGE: November 12, 2013
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Meghna Estuary is located in the south of Bangladesh and is one of the most dynamically deforming estuaries on the earth. The Ganges, the Brahnmaputra, and the Meghna merge with each other and find their way to Meghna Estuary and discharge with huge amount of sediment. The recent coastlines were distinguished by a total of twenty-one PALSAR images from 2007 to 2011. Observed change of the land area was compared with various factors and it was found from the analysis that the morphological change in Meghna Estuary showed seasonal cyclic trend and is strongly related to heavy sediment discharge from the Meghna River and near shore waves. It should also be highlighted that precipitations in the catchment and the observed area change showed strong correlations but has clear phase shift of around 100 days.
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Masatoshi YUHI
2013 Volume 69 Issue 2 Pages
I_641-I_645
Published: 2013
Released on J-STAGE: November 12, 2013
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This study analyzes a bathymetric dataset sampled annually for 51 years along the Ishikawa Coast, Japan, where the morphological variation is characterized by the cyclic cross-shore migration of bars with approximately 10-year return period. Five cycles have been identified from 1960 to 2010. The variability of spatial pattern during individual cycle is analyzed to quantify the characteristics of three-dimensional morphological evolutions. Considerable changes in plan shape were observed such as quasi-regular crescentic patterns, parallel alignment of oblique bars, disconnection and realignment of bars. This is in contrast to the quasi two-dimensional progress of net offshore migration (NOM) of sandbars reported in the Netherlands, New Zealand, Denmark, and Japan.
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Toshiro SAN-NAMI, Takaaki UDA, Toshinori ISHIKAWA, Shiro OIDO, Kazumas ...
2013 Volume 69 Issue 2 Pages
I_646-I_650
Published: 2013
Released on J-STAGE: November 12, 2013
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On the Hamamatsu-goto coast located west of the Tenryu River mouth, beach has been eroded severely in recent years, resulting in the exposure of the seawall protecting the sewage facility. Now urgent measures are required to prevent the damage to the seawall. In particular, large-scale offshore troughs have developed in this area, resulting in strong wave action to the seawall. Erosion around the Tenryu River mouth was investigated using aerial photographs, NMB and bottom sounding data along with the grain size analysis of seabed materials.
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Takumi OKABE, Shigeru KATO
2013 Volume 69 Issue 2 Pages
I_651-I_655
Published: 2013
Released on J-STAGE: November 12, 2013
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In this study, bathymetric data is obtained frequently from operational record (the position by GPS and the depth by fishfinder) of small fishing boats in the nearshore area. Medium-term trends of ebb-tidal delta (ETD) progradation and short-term topographical changes on ETD are detected in comparison of frequent bathymetric data from 2007 to 2012. Analysis of ETD terminal slope (depth of 9-11 m) resulted in 7-9 m/year of annual rate of prograding seaward until June 2011. Bathymetric change analysis shows that concentrated erosion (approximately 2 m vertically) occurred within ETD by effect of high wave condition due to T1106 in July 2011. Longshore sediment transport is estimated from volumetric change of erosion zone on ETD.
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Masatoshi YUHI, Masayuki MATSUYAMA
2013 Volume 69 Issue 2 Pages
I_656-I_660
Published: 2013
Released on J-STAGE: November 12, 2013
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The characteristics of spatiotemporal variation of the multiple bar system on the Chirihama and neighboring beach, Japan, have been investigated using a set of field surveys collected over 13 years and aerial photographs during 1947 to 2010. In the north and middle of the study area temporal variation of sandbar configuration is characterized by the presence of cyclic cross-shore migration with approximately 4 to 6 years return period. The direction of systematic inter-annual migration is net offshore. The migration features indicate substantial alongshore variability. On the north part the behavior of bar system is quasi two-dimensional. On the middle to south area several three-dimensional configuration and deformation such as bar switching and bifurcation are observed.
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Takaaki UDA, Masumi SERIZAWA, Shiho MIYAHARA
2013 Volume 69 Issue 2 Pages
I_661-I_665
Published: 2013
Released on J-STAGE: November 12, 2013
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The interaction of symmetric and asymmetric sand bars enclosing a bay between them due to wave action was investigated using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept). Under the condition that sand spits with asymmetric shape elongate from both shores of a bay, the wave-sheltering effect of these sand spits affecting the other spit differ each other, causing the interaction of the sand bars. This results in the formation of sand bars with characteristic features. The predicted beach changes were compared with the results given by Zenkovich (1967).
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Takaaki UDA, Toshiro SAN-NAMI, Toshinori ISHIKAWA, Yusuke ITO, Norifus ...
2013 Volume 69 Issue 2 Pages
I_666-I_670
Published: 2013
Released on J-STAGE: November 12, 2013
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Shoreline changes along the coasts between the Tenryu River mouth and Point Omaezaki facing the Pacific Ocean were investigated using aerial photographs. Beach has been eroded on the coast located near the east end of the coastline far from the river mouth. Although beach erosion on the Ryuyo and Fukude coasts composing part of the Tenryu River delta was triggered by the decrease in fluvial sand supply and the obstruction of longshore sand transport by a port breakwater, beach erosion on a coast far from the river mouth was due to the effect of ground subsidence along with that of windblown sand.
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Shigeru MIZUGAKI, Junichi OTSUKA, Masahiro MARUYAMA, Hiroki YABE, Sato ...
2013 Volume 69 Issue 2 Pages
I_671-I_675
Published: 2013
Released on J-STAGE: November 12, 2013
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To elucidate the seasonal change, spatial distribution of particle size and source of coastal sediment, monitoring and fingerprinting of coastal sediment were conducted in the Mukawa Coast, the Pacific Ocean of Hokkaido, northern Japan. Statistical analysis among the indices of the particle size and the wave and discharge suggested that the seasonal and temporal variation in particle size can be controlled by fine sand dynamics through the interaction between seasonal change of wave and discharge and geographical condition associated with river mouth and port. The source areas of the fine sand were estimated as upstream and midstream of the river watersheds through the fingerprinting technique using natural radionuclides.
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Shintaro WADA, Syuhei ONUKI, Jun-ichi KADOTA, Makoto IFUKU
2013 Volume 69 Issue 2 Pages
I_676-I_680
Published: 2013
Released on J-STAGE: November 12, 2013
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This study presents the results of flow, topography change and time variation of accretion or erosion rates for a symmetric semi diurnal tide around the Shiogama(namely the deepest region) at Bisan-seto fairway. The numerical analysis was carried out by LES. The flow accelerates and diverges radially during the westward current and converges during the eastward current near the top of slope around Shiogama. These numerical results of flow accord with the measured results by ADP. The accretion and erosion rates of uniform bed are approximately 0.95 times as much as those of mixture bed. The rates of accretion and erosion per unit time are below 0.01 m/h.
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Morika OHMURA, Shinji SATO
2013 Volume 69 Issue 2 Pages
I_681-I_685
Published: 2013
Released on J-STAGE: November 12, 2013
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Kaetsu region has been facing problems of coastal erosion and accumulation of sediments in dams and harbors. This study aims to investigate sediment transport and its long-term changes considering sea level variation. Numerical calculation of waves and nearshore currents, together with analysis of physical properties of sand particles such as thermoluminessence, color and size were conducted to estimate the source and transport direction of sediment over geological time scale. It is found that the changes in the nearshore currents around the Kuzuryu River mouth and sediment supply from old dunes onto the coast north of the Kuzuryu River mouth are essential in understanding the sediment movement in the watershed scale.
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Masayuki BANNO, Koji SEIKE, Junko KOMATSUBARA, Yoshiaki KURIYAMA
2013 Volume 69 Issue 2 Pages
I_686-I_690
Published: 2013
Released on J-STAGE: November 12, 2013
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Sediment deposition and the origins at water depths of 9 to 19 m at Kashima-nada Sea were investigated by radiocarbon dating the age of shells contained in the seabed core samples. The older-than-normal shells were used as tracers, which was included in sediments dumped into the sea from 1965 to 1977, to estimate the offshore sedimentation and sediment transport history. The results showed that the influence of the dumped sediments was observed even at a water depth of 19 m, and it was also indicated that the dumped sediments were not moved in relative deepwater points after the deposition and the dumped sediments eroded after the deposition in relative shallow-water points would be transported and be redeposited.
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Hideo SEKIGUCHI, Hideo YAMAZAKI, Ryota NAKAGAWA, Masanobu ISHIDA, Ryou ...
2013 Volume 69 Issue 2 Pages
I_691-I_695
Published: 2013
Released on J-STAGE: November 12, 2013
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The fluvial supply and littoral dispersal of sediment exert profound influences on the way in which sandy beaches evolve. This paper looks at the importance of flood events in assessing the sediment budget in a littoral cell,with consideration of the grain-size dependency of sediment dispersal. The particular discussion focuses on the impact of a major flood that occurred at the end of July 2011 and brought a significant amount of sediment offshore through the mouth of a river(Okotsu diversion channel). The retrieval and facies analysis of three offshore sediment cores permitted the authors to identify the 2011 flood-event layer on top of each sediment core. The gamma-ray spectrometry revealed that the flood-event layer carried the March 2011 Fukushima-event-associated radioactive nuclides.
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Gozo TSUJIMOTO, Masahiro TAMAI, Sota NAKAJO
2013 Volume 69 Issue 2 Pages
I_696-I_700
Published: 2013
Released on J-STAGE: November 12, 2013
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The direction of sediment transport is one of important factors to manage sandy beaches. The prominent direction of sediment transport was estimated using grain size parameters such as the mean, sorting, skewness and roundness. They were obtained from digital images. The agreement between grain size distribution profiles by a sieving technique and by digital images is good. With decreasing of grain size diameter, grain shape becomes more round. Also distribution profiles of grain roundness are corresponding to normal distribution profiles. The prominent direction of sediment transport in Awaji Island has both southwest and northeast\. The significant level of Z-score increases by considering grain roundness.
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Akio KOBAYASHI, Takaaki UDA, Masatoshi ENDO, Kouta MASUDA
2013 Volume 69 Issue 2 Pages
I_701-I_705
Published: 2013
Released on J-STAGE: November 12, 2013
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Ground subsidence by 22 cm occurred in Lake Hinuma in Ibaraki Prefecture during the 2011 Great Earthquake on March 11, 2011. This lake is connected to the Pacific Ocean via the Hinuma and Naka Rivers, resulting in the sudden increase in water level of the lake by 22 cm. This increase in water level was larger than the mean significant wave height of normal waves in Lake Hinuma, and thus large impact to the sandy beach and shoreline vegetation was caused. Field observations were carried out to investigate the impact as well as the impact of a groin constructed before the earthquake.
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Takaaki UDA, Takayuki KUMADA, Yasuhito NOSHI, Yoshiaki ARASHIBA
2013 Volume 69 Issue 2 Pages
I_706-I_710
Published: 2013
Released on J-STAGE: November 12, 2013
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On the Hokota coast facing the Pacific Ocean, beach changes have occurred in response to the seasonal variation in wave direction and wave height. Aerial photographs were taken to investigate shoreline changes around Nos. 23 and 29 artificial headlands. Numerical simulation using the BG model improved by Noshi et al. (2009) was carried out. The seasonal changes in beach topography and grain size of bed materials were reproduced. Furthermore, beach changes when submerged groins were extended offshore of Nos. 23 and 29 artificial headlands were predicted.
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Yoshiyuki IZUMI, Hitomi ITO, Hiromi MUKASA, Takaaki UDA, Kazuya SAKAI, ...
2013 Volume 69 Issue 2 Pages
I_711-I_715
Published: 2013
Released on J-STAGE: November 12, 2013
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On the Ninomiya coast, two groins of 50 m length with an opening of 300 m were constructed as a measure preventing longshore discharge of nourishment sand, and then beach nourishment using 16,400 m
3 of the riverbed materials of the Sakawa River were carried out by July 9, 2012. Storm waves of Typhoon No. 5 hit the coast on June 19, 2012 and 10,900 m
3 of beach materials discharged by storm waves. The effect of beach nourishment using coarse materials on this coast was investigated by field observation along with the numerical simulation using the contour-line-change model.
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Puangpet RATTANARAMA, Arjong NOPMUENG, Yoshimichi YAMAMOTO
2013 Volume 69 Issue 2 Pages
I_716-I_720
Published: 2013
Released on J-STAGE: November 12, 2013
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In many coasts of Thailand, serious coastal erosion has occurred and breakwaters for preventing it have been constructed. Especially since many coasts in the gulf of Thailand consist of very fine bed materials, wave dissipation breakwaters made of bamboo piles and detached breakwaters made of geotextile bags which were packed bed materials have been constructed instead of concrete block breakwaters. However, these arrangement plans were based on empirical techniques. This research examines the validity of the effect evaluation method of the coastal erosion prevention using a numerical prediction model. Moreover, the comparison of the bamboo pile breakwater and the geotextile detached breakwater shows that the former can acquire sufficient effect for the erosion prevention with construction costs cheaper a little than the latter.
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Shinya MOTOJIMA, Akio KOBAYASHI, Takaaki UDA, Masatoshi ENDO
2013 Volume 69 Issue 2 Pages
I_721-I_725
Published: 2013
Released on J-STAGE: November 12, 2013
JOURNAL
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On the Oharai-Isohama coast, 1×10
4 m
3 of gravel and 2.5×10
3 m
3 of fine sand were nourished in April and May 2012 as a measure against beach erosion. Simultaneously tracer test was carried out using 100 m3 of granite gravel with a diameter of 20 cm, which was not deposited on the original beach. Granite gravel was placed on the shoreline, and subsequent movement was measured using GPS along with the measurement of the diameter of the gravel. It was found that gravel was transported northward and deposited on the shoreline.
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Kenji NOGUCHI, Yoshio SUWA, Kunihiro WATANABE, Kazumori YOSHIKURA, Yuk ...
2013 Volume 69 Issue 2 Pages
I_726-I_730
Published: 2013
Released on J-STAGE: November 12, 2013
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Unconsolidated sand dune is vulnerable to ran-up wave attacks. Adding,recovery of its volume is difficult. To protect the foot of sand dune scarp is important to the crest height conservation. We evaluated effects of the “Sand Dune Scarp Control Works” with an experimental construction. The objects were experienced four typhoon attacks. Beach profile change was caused by beach cusps and mega cusps. We confirmed their effect to protect dune and innocuity to onshore sediment transport.
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Takaaki UDA, Yukiyoshi HOSHIGAMI, Kazuya SAKAI, Yasuhito NOSHI
2013 Volume 69 Issue 2 Pages
I_731-I_735
Published: 2013
Released on J-STAGE: November 12, 2013
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On the Takata-matsubara coast, sandy beach was severely eroded by the return flow of the 2011 Great Earthquake Tsunami occurred on March 11, 2011. The recovery of sandy beach was planned using beach nourishment. In this study, the effect of beach nourishment using relatively coarse materials such as the grain size of 1 mm was investigated using the BG model. Because three artificial reefs with a crown depth of 3 m have been constructed before the earthquake on this coast, beach changes due to these artificial reefs were taken into account.,
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Takaaki UDA, Susumu ONAKA, Masumi SERIZAWA, Masatoshi IZUMI, Toshiro S ...
2013 Volume 69 Issue 2 Pages
I_736-I_740
Published: 2013
Released on J-STAGE: November 12, 2013
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A plan of beach nourishment using coral sand and gravel on the lagoon side of Fongafale Island in Tuvalu was investigated. Field observation was carried out on June 5, 2012 and the formation of the composite slope of an offshore gentle slope covered with sand and a steep foreshore slope covered with gravel was confirmed. On the basis of this fundamental information, a method of gravel nourishment together with use of sand was investigated using the BG model. When two groins with 40 m length and an interval of 185 m were constructed along with beach nourishment, it was possible to recover the stable beach.
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Satoshi TAKEWAKA, Seunghyun AN
2013 Volume 69 Issue 2 Pages
I_741-I_745
Published: 2013
Released on J-STAGE: November 12, 2013
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Field observation on spatial and temporal variation of shoreline positions along a 16 km-long sandy beach forming a littoral cell was conducted with four X-band radars in year 2010. Half of the coast is protected by jetties,locally known as Headlands,and the rest is close to natural state exposed to the ocean. Hourly shoreline position variations at the Headland were decomposed with Empirical Orthogonal Function analysis into non-synchronizing and synchronizing modes. Non-synchronizing modes are the most prevailing constituent,having opposite signs on both sides of the Headland. These are due to trapping of the longshore sediment at the Headland,and showed a moderate correlation with longshore wave energy flux and migration speeds of coastal features observed at the research pier which locates in the natural section.
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Katsuya HIRAYAMA, Kiyomitsu KAWAUCHI, Ichiro MIYAZATO, Kazuhiro TANAKA
2013 Volume 69 Issue 2 Pages
I_746-I_750
Published: 2013
Released on J-STAGE: November 12, 2013
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A wave overtopping rate for a seawall on coral reef may be evaluated with the estimation diagrams of it on sloping beach, which is proposed by Goda & Kishira (1975). To do this, Miyakuni et al. (2008) have suggested that wave set-up and surf-beat should be added to the design water depth which is applied on them. Moreover, Hirayama et al. (2009) have indicated that such design conditions on a coral reef can be calculated by using the Boussinesq-type wave transformation model developed by Hirayama & Hiraishi (2005). In this study, an applicability of such estimation method is verified with the results of model experiments which are carried out on a horizontal basin, and it is confirmed that the calculations of wave transformation on coral reef should be conducted with the topography installed the designed seawalls.
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