Tsunami-induced local scouring at the landward toe of a coastal dike is investigated experimentally and numerically in terms of the process of the scouring, the response of the foundation, and the stability of armor blocks. From a comparison between experimental data and numerical results, the predictive capability of a numerical model taking into account fluid-sediment-seabed interactions is demonstrated in terms of water surface elevations and scour profiles. Furthermore, it is found that armor blocks below the top and berm of the landward slope of the dike receive large landward and upward force because of an increase in air pressure inside the dike and a decrease in water pressure induced by flow separation, suggesting that these blocks would be vulnerable against tsunami overflow.

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The Great East Japan Tsunami in March, 2011 caused the significant changes of morphology on Sendai Coast. The flushing of sand spit in front of Nanakita River mouth and the breaching at Akaiko area can be observed. This study investigates the erosion of shoreline on the right side of Nanakita River mouth and the recovery of the breaching after the tsunami. Estimation of diffusion coefficient, which is an important parameter in numerical simulation of shoreline change, has been carried out for both study areas from measured data of erosional area propagation. These values of diffusion coefficient have been used to reproduce the erosion and the recovery of shoreline positions at study areas. The results show good agreement between the analytical result and measurement.

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Morphological changes and recovery process at the Natori River mouth were evaluated by using the aerial photography and the observed cross-sectional data. The river mouth morphology has changed completely due to the 2011 Tohoku Tsunami. Since then, there is in the process of recovery. The result of the analysis shows that the morphological changes of the river mouth become stable condition. Furthermore, the relationship between tidal prism and inlet cross-sectional area was used to determine the current state of the Natori River mouth. It indicates that the river mouth condition has been returned to the past state before the 2011 Tohoku Tsunami. This study presents the influences of the river mouth structure in analyzing morphological changes and recovery process. It is also considered the practical problems in this area.

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The causes of beach changes on south Kujukuri Beach facing the Pacific Ocean were investigated on the basis of aerial photographs and the data set of the long-term measurements of the ground level by the Chiba Prefectural Government. On this coastal lowland, ground subsidence owing to the pumping-up of the water-soluble gas reached 90 cm between 1968 and 2012, resulting in the shoreline recession by 18 m given the foreshore slope of 1/20. Furthermore, ground subsidence of 9.3 cm occurred by the crustal movement during the 2011 Great Earthquake. These factors affected the beach changes.

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Recovery of sandy beach from severe erosion by the 2011 tsunami can be observed on Sendai Coast even 3 years after the tsunami. The long-term effect of such a severe morphology change on sediment transport system is investigated through analysis of aerial photographs. Empirical Orthogonal Function (EOF) analysis is applied to shoreline positions extracted from the aerial photographs. The first and third modes express the recovery process of shoreline from the severe erosion with respective time-scale, and the superposition of their contribution rate is more than 70%. Comparison of shoreline change rate before and after the tsunami clearly shows that the recovery process of severely eroded area caused completely different trend of sediment transport processes.

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The response of the sandy beach to the 2011 Great Earthquake and Tsunami was investigated through the comparison of the shoreline changes between Oarai and Kashima Ports using satellite images before and after the earthquake, taking the Kashimanada coast as an example. Although a large amount of sand was deposited inside Kashima Port during the tsunami, dredged material was used for the offshore nourishment in 2011 and 2012 to maintain the coastal environment. The effectiveness of offshore nourishment to maintain the offshore seabed was revealed.

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To evaluate the shoreline retreat caused by sand dredging at offshore bars, a series of experiments were conducted in a 2D wave flume. Various amounts of sand were dredged at an offshore bar model formed by regular waves and the change in the beach profile was observed under the same or different wave condi-tions. Different dredging methods, i.e. one-time and periodic dredging were also tested to observe the in-fluence of the dredging method on the shoreline change. The results showed that the shoreline retreat in-creases as the dredging volume increases although the relationship between the two is not linear. The characteristics of shoreline retreat were investigated in terms of beach profile change, sediment transport rate, and wave height distribution. The applicability of Dean's formula, used to estimate shoreline change by beach nourishment, is also discussed.

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The morphology and suction dynamics of intertidal multiple sand bars is examined to provide insight into the factors controlling the bar characteristics. Field experiments over the intertidal sand waves show that the vane shear strength near sediment surface increases with suction behavior. Richards equation which expressed suction and ground water dynamics were used in numerical model. The laboratory experiment which imitates the ebb and flow upon sandy flats was used for validation of proposed model. In numerical experiment of tide-dominated conditions which mean quite small bedload effects, morphlogical changes show close relationships with suction dynamics due to suction-induced void state changes.

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Kujukuri Beach has been eroded owing to the decrease in sediment supply from sea cliffs and the obstruction of longshore sand transport by fishing port breakwaters. Eroded zone has been expanding rapidly to the central part of an arc-shaped 33 km long shoreline. Not only beach changes but also grain size changes occurred because fine sand can move faster than coarse sand. These changes were predicted using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept). The effect of beach nourishment using fine and coarse material was also investigated.

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This study developed a semi-empirical equilibrium-based shoreline change model, which was a nonlinear mixed-effect model allowing for random effects at equilibrium foreshore profiles. Using the model, the long-term uncertainties of equilibrium foreshore profiles, which were derived from such incompleteness of the model equation and latent variables unconsidered in the model were investigated. The model was applied to the longitudinal sandy beach profile data obtained at the Hasaki coast of Japan. The result showed that the uncertainties had the equilibrium foreshore profiles move parallel to the cross-shore direction, which resulted in foreshore deposition and erosion over several years and the slope of the equilibrium foreshore profile grew steeply with time by the uncertainties.

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Geographical features around the Hasaki Oceanographical Research Facility have been changed extremely by a big storm in October, 2006. Using topographical survey and particle size analysis data from 2005 to 2011, the relation between geographical features and the grain-size composition is shown. Before the storm, features and the grain-size tend to repeat the following two stages. Stage I: The foreshore slope is uniform by the long period wave run-up and median grain-size is medium sand at the shoreline and fine sand at the wave run-up end. Stage II: The slope is varied by the incident wave at the calm and the grain-size is medium sand at the berm. After the storm, features and the grain-size become a different stage. Stage III: The slope is steep and the high berm is formed along the coast with coarse sand.

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The correlation between foreshore beach profile change, especially berm erosion, and groundwater level fluctuation was considered using a numerical model, XBeach (Roelvink et al., 2010). After conducting the model verification with the observed field data, the correlation was analyzed by numerical experiments. From the numerical experiment analysis, when the groundwater level was controlled to an original level at some regular time interval, although the berm erosion occurred as the same as the un-controlled case, the berm erosion volume is reduced.

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A short-term swash zone beach profile change model originally proposed by Suzuki and Kuriyama (2009) focusing on berm formation and erosion was generalized in order to apply this model to another sandy beaches. The generalized model was applied to the calculation of three months beach profile change, which results were compared with field data and the computational results of the previous model. Also, the model was applied to the calculation of one year beach profile change and compared with field data. The present model was found to well predict not only the shoreline change but also the beach profile change, including the berm formation and erosion, for both short term and long term calculations.

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Notsukezaki is the longest sand spit in Japan, located in the east region of Hokkaido, and the waves and morphology vary along the spit. The main purpose of this study is improving one-line simulation model by optimization of input parameters, and applying this improved model to Notsukezaki. We set boundary condition by investigation of field observation, input time series wave data in every 6 hours from GPV-wave model, and changed the closure depth according to every wave condition. Results of calculation show that the model can predict well the shoreline changes on Notsukezaki.

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Fluvial discharge from the rivers is viewed as a missing piece for the inventory of the radionuclides in the ocean during the accident at the Fukushima Daiichi Nuclear Power Plant. The land-derived input introduces a time lag behind the direct release through hydrological process because these radionuclides mostly attach to suspended particles (sediments) that are transported quite differently to the dissolved matter in the ocean. We therefore develop a regional sediment transport model consisting of a multi-class non-cohesive sediment transport module, a wave-enhanced bed boundary layer model and a stratigraphy model proposed by Blaas et al. (2007) based on ROMS.

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Ultimate goal of this study is to understand how the sediment, placed as part of reclamation work, behaves on eroding beach. Field reclamation experiment has been carried out at the Murozumi coast in Yamaguchi prefecture and sand with two different colors, blue and green, was also placed as a tracer. To enhance the temporal and spatial resolutions of the tracer survey, this study aims to develop an image-based technique for estimation of the rate of color sand grains from the on-site images of the beach sand surface directly taken by a GPS digital camera. Validity of the newly developed image-based technique was examined through comparisons with the data obtained from sampled sand. Obtained movement of color sand was then compared to the morphology change around the reclaimed area captured by field camera.

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A 3D numerical model is created to study the sorting behavior of mixed-grain-size sediments in oscillatory sheet flow, including both particle-particle interaction and particle-fluid interaction. Additionally, beside this symmetry sinusoidal oscillatory flow, the sorting processes of mixed sands in asymmetry progressive cnoidal wave are also numerically investigated. The results of mixed sand under symmetric oscillatory flow show that the water particle semi-excursion is a key influence factor on the armoring effect. For the cnoidal wave, the vertical sorting proceeds until the wave crest passes by and fully develops in a complete period. The concentration centroid of large particles becomes higher landward within 2 periods.

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The initiation of sediment motion under waves has been studied to develop a simple empirical model for determining critical Shields parameter and critical velocity of fine sand. It is found that the Shields parameter linearly proportional to the relative wave height with respect to water depth. The onset relative wave height of sediment motion is governed primarily by a non-dimensional parameter consisted of grain size, water depth and wave period. The explicit formulas of both Shields parameter and critical velocity are derived from four different series of available experimental data obtained from small wave flume tests. The present model is simple and agrees well with the results of large wave flume test. For a given fine sand, the onset velocity derived from the present model is increased with increasing wave period and decreasing water depth.

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Headland is a coastal structure to control longshore sediment transport. This study focuses on the annual variations of shoreline configurations around three headlands established along a long sandy beach at Kashima coast, Ibaraki. With results of radar measurement, shoreline position, intertidal beach slope, and beach volumes are estimated by data analyses. Seasonal features of shoreline position are discussed in terms of seasonal wave conditions. Morphology around headlands and locations of breaker line are examined.

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Lakeshore changes associated with the extension of an offshore breakwater in a lake were investigated, taking the Torigasaki cuspate foreland located on the south shore of Lake Shinji as an example. After the construction of a long breakwater to form a wave-shelter zone, a cuspate foreland was formed with shoreline recession on the nearby coast. The shoreline changes were investigated using aerial photographs, and the beach changes were reproduced using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept). The predicted and measured beach changes were in good agreement.

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Recently, estuary choking occurs several times in Toufutsu river mouth every winter, and the dredging is carried out after occurrence of estuary choking. Estuary choking affect flood control, fisheries in lake, and so forth. In this study, we aimed to reveal the mechanism of estuary choking by observations, which are current observation, water level observation, sediment survey, and video monitoring at the entrance of the Toufutsu Lake. Followings were major accomplishments of this study. (1)When high tide level during the flood tide and incident wave from the right bank side occurred at the same time, estuary choking occurred in Toufutsu estuary. (2) In case that ground level of inland area is higher than the crown height of the revetment, estuary choking is likely to be caused by swash.

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The second inlet of Saloma Lake was made in 1979, and was closed by sand transport at first time at January 2012. The characteristics of topography change from 2001 to 2012 around the Inlet were understood. Primary factors of this closing phenomenon are the increase of long shore sediment transport towards left caused by waves, and the increase of discharged sediment from Tokoro River. The increase of discharged sediment was caused by increasing rain fall because of the global warming, and this phenomenon is happening in a long term. The change of ocean wave direction can be estimated by the change of sun spot number with about ten years period.

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In vast areas of the Arctic Coastal Plain, groups of lake basins with a common long-axis orientation, oriented lakes, can be found. Numerical simulation using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept) was carried out, and the characteristic of oriented lakes that the direction of their principal axis is perpendicular to the principal axis of probability distribution for the occurrence of wind direction was successfully explained. The predicted results and the examples given by Seppälä (2004) were in good agreement.

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The effect of hydro-oceanographic conditions of river mouth morphology on sandy beach was examined by the systematical experiment on variation of river discharge, sea level, and wave height and wave length. River mouth morphology was classified as three categories, stable channel with river mouth opened, meander channel which sand bar extends greatly, and barrier-spit channel formed by long sand bar. Finally, the effect of the position of an offshore breakwater affected on river mouth morphology was clarified by experiment.

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Sounding surveys were carried out to monitor topographic change around the Tama river mouth in Tokyo Bay every half year for 7 years since 2006 through 2013. Comparison of sounding data measured on the same cross sections in the river mouth provides the trend of temporal topographical changes during the monitoring period. Elevation changes averaged over the target area are around 10 cm for half year and they have increased corresponding to the extent of fresh water discharge during the period between the sounding surveys. In periods experiencing relatively large flood, depositions of sediments are prominent especially in the deeper channels with the order of 1 m, although the range of variations in shallow area are smaller than the channel portion with the range of at most few decimeters.

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This study presents bathymetric changes and its characteristics due to high waves and fluvial floods are examined for river mouth terrace in a wave-dominated estuary of the Tenryu river,a sediment-rich river on the Pacific coast (Enshu-nada) of central Japan. Frequent continuous nearshore bathymetric data of the river mouth terrace and vicinity are obtained from records of whitebait fishing activity by small vessels. Dominant feature of 5-year bathymetric trend are exhibited by concentrated erosion (approximately 3 m vertically) within the front of river mouth and the frontal lobe of terrace migration. Wave-induced retrogradation and flood-induced progradation of the terrace front during meteorological event are examined by transect analysis of the lobe.

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Field observations were conducted on the morphology and hydrodynamics around the Tenryu River mouth. The sand bar was eroded by storm waves followed by flood due to the typhoon in September, 2013, which significantly changed the water level variations inside the river mouth. The large friction at the narrow opening of the river mouth was found to raise the daily-averaged river water level by 0.2 m. The presence of and bar appeared to decrease the intrusion of tides and waves into the river. The transmission coefficient of waves increased from 0.2-2 % to 2-5 % as the cross-sectional area at the river mouth was increased. The water level variation due to tides and wave setup was found even at 3 km upstream from the river mouth.

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Morphological changes at the river mouth of Tenryu by floods and waves are observed continuously with a X-band radar for years 2010 and 2011. X-band radar grasps the shapes of the river channel and sand bar,and the submarine extent of river terrace formed at the seawards of the river mouth. When the river water level increases,flood flow erodes the sand bar,and sediment is fed to expand the river terrace. After the flood,recover of the sand bar starts and its tip migrates to close the river by the action of oblique incident waves. At the same time,river terrace starts to shrink also by the action of waves. The amounts of these changes were estimated from the result of X-band radar observation and were reasonably well correlated with the flood intensities and wave energy fluxes.

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The formation mechanism of a tombolo behind Oki Island in Tateyama Bay was investigated using aerial photographs together with beach survey data. This tombolo was formed on a shallow seabed, which was lifted by 1.6 m during the Kanto Earthquake occurred in 1923. Sand supplied from the Kanita River flowing into south of Oki Island was transported by longshore sand transport generated by wind waves incident from the west. The rate of longshore sand supply was estimated to be 215 m3/yr and windblown sand in winter was another important factor on beach changes.

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Using digital images of sand grain with a scanner, the training data set on minerals; quartz, feldspar, shale silicified stone and chart was made. The data set could be divided into five regions using the CIEL*a*b* color space methods. Especially color brightness and satulation are important to identity mienrals. Shapes of quartzs and feldspars are more rounder than other minerals. Filed observations were carruied out in Awaji Island and 17 samples of beach sand and 51 river were colleceted. The optimiation method was applied to estimate the impact rate from rivers toward beaches with a distance among a beach and a river. The estimated results are corresponding to the existing knowledge.

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Sediment budgets of the Kashima-nada have been unknown because the sediment discharge from the Naka River has not been well known. In this study, sediment discharges of the suspended load and the bed load from the rivermouth of Naka River were estimated by using the turbidity meter and ADCP. The bed load discharge was observed by using the bottom-track speed of ADCP and the Egashira equation. Observation and calculation results soon after the flood were well agreed with the Ashida-Michigami equation and the M-P&P equation, so that the bed load discharge at the peak flood was calculated by using the former equation and the friction velocity u* estimated by g, R and I. The result of estimation was that the suspended load discharge was 34,892 m³ and the bed load discharge 28,356 m³ through the year. In conclusion, the total discharge was estimated at 63,248 m³ and it was almost agreed with the another estimation.

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Topographic changes around the tip of Mihono-matsubara Sand Spit with the development of a steep slope owing to the succesive sand deposition into the deep water were investigated using bathymetric data. Then, numerical simulation of the elongation of sand spit on a sloping seabed with different water depth and slope was carried out using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept), and the relationship among the sand volume comprising the sand spit, the planar area of the sand spit, and the length were investigated.

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On the Omaezaki coast, not only beach changes owing to the imbalance of longshore sand transport but also those owing to ground subsidence triggered by crustal movement have occurred. The effect of crustal movement to the beach changes was included in the BG model, and the BG model was expanded to predict the long-term beach changes, taking both beach changes owing to ground subsidence triggered by crustal movement and beach changes owing to waves into account. The numerical simulation results and measured shoreline changes were in good agreement.

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In 2013, Mt. Fuji was designated as the world culture heritage with Mihono-Matsubara which has a famous spot of Hagoromo-no-matsu (Hagoromo Pine trees) as one of the primary components constituting the coastal scenery of Mt. Fuji from the shoreline. New measures against beach erosion which do not spoil the coastal scenery were requested. Upon these requests, beach changes between No. 4 artificial headland south of L-shape groin and transect No.1 near Shimizu Port were investigated and the longshore sand transport in recent years was estimated. Basic plan of the measure was also discussed.

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At Mihono-Matsubara on the Shimizu coast, new measures against beach erosion which do not spoil the coastal scenery of Mt. Fuji from the shoreline were required since the designation of Mt. Fuji as the world culture heritage in 2013. In this study, the effect of some measures including L-shape groins against beach erosion was analyzed by numerical simulation using the contour-line-change model considering the grain size. The most effective measure was the installation of four L-shape groins with the sand back pass by a rate of 5×10⁴ m³/yr from the north end of the sand spit.

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Shoreline changes along the coasts between Point Omaezaki and the Katsumata River mouth in Suruga Bay were investigated using aerial photographs. Although northward longshore sand transport was predominant before the construction of the Omaezaki Port breakwater, the direction of longshore sand transport reversed owing to the effect of the formation of the wave-shelter zone by the port breakwater. In addition, the effect of ground subsidence associated with crustal movement was superimposed to these beach changes.

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Trenches were excavated to observe the sedimentary strata on three beaches in Shizuoka, Japan. The western trench was near the Abe River, which is the source of sediment transport; the eastern trench was on the Miho Spit that marks the end of the longshore sediment transport, and the third was in between the two. The strata of the walls of the trenches were recorded and the grain-size distribution of each stratum analyzed. It was found that the grain-size accumulation curve could be divided into five groups based on the ratio of gravel to sand. This shows that conditions of sediment transport affect sediment content. Trench wall strata provide evidence of the strata-forming events.

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Taking the Fuji River which is the major source of sand to the Fuji coast as an example, the sand deposition caused by floods was investigated using the Narrow-Multi Beam surveys as a fundamental study of the comprehensive management of sand movement. During the observation period in 2011, three large floods with discharges of 3,340, 5,985 and 13,319 m3/s occurred during Typhoon 6, T12 and T15, respectively. Approximately 4×10⁵ m³ of sand was found to be supplied to the river mouth in each flood.

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On the Hamamatsu-Shinohara coast, beach nourishment using gravel was started in 2005, and monitoring surveys have been carried out since then. The analysis of the volume of sand deposited in the nourishment area showed that 1.8×10⁵ m³ of sand was left behind until February 2013 after the nourishment of 8.63×10⁵ m³ between 2005 and 2013, implying that the sand volume supplied in this period was 6.5×10⁵ m³. After a large amount of gravel was nourished, waves were incident almost from the direction normal to the shoreline, resulting in the shoreline advance near the nourishment area, even though high waves were incident.

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On the Hamamatsu-Shinohara coast, beach nourishment using gravel has been carried out since 2005. The beach changes on this coast were reproduced using the BG model (a three-dimensional model for predicting beach changes based on Bagnold's concept). Then, the beach changes after 20 years were predicted, and the effect of beach nourishment using coarse material was evaluated along with the evaluation of the beach nourishment using sand deposited in the reservoir upstream of Akiba Dam. It was concluded that the effect of the cancellation of beach nourishment appears in the long-term, beach will be gradually eroded, even though the contents of grain size of nourishment materials are altered, and beach width could be maintained by the nourishment using sand deposited in the reservoir upstream of Akiba Dam.

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As a measure against beach erosion, beach nourishment using coarse material has been carried out since 1996 east of the Showa Floodway on the Fuji coast, and 1.53×10⁶ m³ of gravel was nourished until 2013. In this study, the shoreline changes of the coast were investigated using aerial photographs together with the analysis of the data set of the Narrow Multibeam survey, which was initiated in 1996, and bottom sampling. The effectiveness of beach nourishment using gravel was investigated as well as the future measure to solve the issue caused by the lack of sand.

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Beach nourishment using coarse material has been carried out since 2012 on the Ninomiya coast, where beach was severely eroded owing to storm waves associated with Typhoon No. 9 hit on September 6, 2007. Beach nourishment was carried out in the area separated by two groins 300 m apart. After the beach nourishment, stable sandy beach was recovered and 89.9% of nourishment gravel was found to be left, implying the effeciency of beach nourishment using coarse material.

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A numerical simulation of the beach changes on the Seisho coast was carried out using a contour-line-change model considering changes in the grain size. The applicability of the simulation model to a gravel-sand beach with protruding rocks was verified by comparing the calculated and observed changes after storm waves generated by T0709. The sand transport controls achieved by different types of coastal facilities were estimated and compared under an imaginary wave condition that could occur in future. A newly-designed groin with a low crown height was found to be most effective in preserving a straight coastline, if a sufficient amount mount of sand will be supplied by beach nourishment.

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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 Inosakinotsugai in Bisan-seto fairway. Sediment accumulates at the region which is locally dredged and the volume is approximately 19,775 m³ during 7 years. The numerical analysis was carried out by LES(Large Eddy Simulation). 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 volume of sediment which accumulates in the pocket is approximately 4.0 m³ during a semi diurnal tidal cycle and this value is approximately 0.85 times as much as it of measured one.

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An assessment framework was developed for the erosion control project in Miyazaki Coast, which is composed of sand nourishment combined with construction of groins and buried seawalls. Key parameters used in the monitoring surveys were selected on the basis of characteristics observed in coastal processes of Miyazaki Coast. The impacts of project were evaluated by comparing predicted values of each parameter assessed by numerical models and those measured in the monitoring surveys. The evaluation accounted for the variable range of the parameter in addition to the trend. Impacts on ecosystems and beach utilization were also evaluated. The framework was found to be useful in extracting appropriate actions.

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Coral cays may be formed by the high waves in about several days. If the initial formation mechanism of coral cays can be understood, it will be useful for protection, the environmental preservation, and use of the coral reef seashore. Moreover, it can contribute also to protection of islands in Japan and the Pacific Ocean archipelagic country where the sea level rise due to global warming may result in submersion. In this paper, 3-dimensional hydraulic movable bed model tests were conducted to clarify the coral cays formation and maintenance process. Consequently, it turned out that wave breaking at leaf edge, the relative relation between leaf size and wavelength, and the cover effect of the wave and current by formation of the coral cays are important for the coral cays formation and maintenance process.

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Correspondence of the long-term trend of shoreline position and wind wave height changes on the Akita southern coast is verified through analyzing the variance, standard deviation and variation coefficient of both the field survey data, collected for more than the last 22 years, of shoreline position and observation data of wind wave height at the Sakata port offing for the same period of more than 22 years, and then comparing these analyzed results. Through the verification, it is confirmed that the standard deviations of the shoreline position and wind wave height changes on the Akita southern coast are gradually increasing with the years, and the time-dependent change pattern of both standard deviations is substantially the same.

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An improved measurement system was developed to quantify the sediment flux on the basis of two image-based techniques for sediment concentration and velocity measurement respectively. Motion images of sediment particles in target flow are recorded by a high-speed camera with an electro luminescence sheet as a backlight source. A stroboscope is synchronized with the camera through a time delay generator at half of the frame rate. Normal (backlight only) and strobo-illuminated images are alternatively obtained for image analysis. Sediment concentration is estimated from normal images according to a pre-calibrated relationship between concentration and light attenuation based on the Lambert-Beer law. Velocities of sediment particles are obtained by applying PIV to each set of the normal and strobo-illuminated motion images. Sediment flux can be figured out by multiplying the concentration and velocity at respective locations. Simple verification tests were conducted to demonstrate the feasibility of the improved system. The results suggest that the system is capable of measuring sediment concentration over 190g/L with errors of no more than 10%.

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A laboratory study under swash flow on a steep slope was designed to investigate the characteristics of bottom boundary layer. By careful setup of the PIV system and optimizing the traditional cross-correlation algorithm, the velocity fields within this thin boundary layer of an order of 1 mm were successfully resolved over ten points. The spatially and temporally resolved near-bed velocity profiles had higher resolution than previous studies and were expected to make reliable insights into the boundary layer structure, including the mean velocities, turbulence intensity and bed shear stress. Results suggested that mean velocities and tur-bulence intensity in uprush are larger than that in the backwash. The uprush flow is associated with the bore-generated and bed-generated turbulence, while the backwash flow is supposed to be dominated by bed-generated turbulence, and the high turbulence intensity in the final stage of backwash is supposed to be related to high velocity gradient. The bed shear stress estimated by fitting the logarithmic profiles to the measured velocity profiles in the uprush was larger than that in the backwash. The detailed measurement data can be used to develop and verify numerical models for boundary layer studies under swash.

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Interactions between contacting and colliding particles associated with energy dissipation mainly dominate sediment transport under oscillatory sheet-flow regime, where hysteretic-dependent complicated behavior dominates over periodical one due to a change in microscopic particle configuration even under the fully periodically oscillatory external forces. Difference in response time between solid particle and carrier phase to oscillatory flow furnish momentum transfer, resulting phase-dependent particle stress should be estimated to ascertain detail mechanism of the sheet-flow regime. In the present study, particle velocity under oscillatory flow is extracted from video sequence taken through the sidewall, accordingly phase-dependent particle shear stress is revealed.

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