Toshiyuki Asano

TWO-PHASE FLOW MODEL ON OSCILLATORY SHEET-FLOW

Tanah Lot Temple is situated in Tabanan Regency - Bali, on the coast of the Indonesian Ocean. Due to continuous wave attack, wind force, and weathering of the rock bank where the Temple stands, abrasion has occured which is more and more threatening the existence of the Temple. Considering that Tanah Lot Temple is a sacred place for the Hindu Balinese people and a place of high cultural value, and also an important tourism, steps to save the Temple are imperative. The Central as well as the Regional Authorities, and also the Bali nese community are very much interested in the effort to keep the Temple intact. Measures have been undertaken to protect both the seaside and land-side banks of the Temple rock bank. This paper only discusses counter measures of the sea —side bank of the Temple.

Sediment accretion and variability of sedimentological characteristics of a tropical estuarine mangrove: Kemaman, Terengganu, Malaysia

This paper reports on a study of accretion rate and sedimentological variability in a estuarine mangrove swamp. One hundred and sixteen stations were monitored for 2 years. In addition, surface sediment samples were collected at 52 stations during the months of May, June and July (1994) to represent the non‐monsoon sediments and November, December (1994) and January (1995) to represent the monsoon sediments. Results show that the accretion rate for the first year was 1.46±0.13 cm/yr and 0.66±0.04 cm/yr for the second year thus making the average accretion for the 2 years period to be 1.06 cm/yr. The average accretion rate for the monsoon season (0.26 ± 0.04 cm/month) was found to be significantly higher than the non‐monsoon season (0.12 ± 0.03 cm/month). Nevertheless, the same is not true for the surface sediment characteristics. The sedimentological characteristics between the monsoon and the non‐monsoon sediments were not significantly different.

Initial tsunami source estimation by inversion with an intelligent selection of model parameters and time delays

We propose a method for accurately estimating the initial tsunami source. Our technique is independent of the earthquake parameters, because we only use recorded tsunami waveforms and an auxiliary basis function, instead of a fault model. We first use the measured waveforms to roughly identify the source area using backward propagated travel times, and then infer the initial sea surface deformation through inversion analysis. A computational intelligence approach based on a genetic algorithm combined with a pattern search was used to select appropriate least squares model parameters and time delays. The proposed method significantly reduced the number of parameters and suppressed the negative effect of regularization schemes that decreased the plausibility of the model. Furthermore, the stochastic approach for deriving the time delays is a more flexible strategy for simulating actual phenomena that occur in nature. The selected parameters and time delays increased the accuracy, and the models ability to reveal the underlying physics associated with the tsunami-generating processes. In this paper, we applied the method to the 2011 Tohoku-Oki tsunami event and examined its effectiveness by comparing the results to those using the conventional method.

Effect of Reflective Structures on Undertow Distribution

/Uastraot: The study investigates the effects of reflective seawalls on wave breaking processes and mean flow distribution throughout the surf zone. The presence of reflective structures results in a significant change of wave breaking characteristics and turbulence structure in the surf zone. The organized large vortexes, which cause onshoreward mass transport, will also be changed thus changing the undertow considerably. The physical processes and mechanisms of wave breaking and turbulence structures in presence of a seawall have been investigated using visualization techniques. A model for evaluating the distribution of undertow in front of a reflective structure is also proposed on the basis of the change in wave fields due to the presence of reflected waves in the surf zone. The model is in reasonable agreement with the experimental results. It has been found that the presence of reflected waves due to reflective condition in the surf zone changes the wave breaking characteristics and reduces the magnitude of undertow. The results of the present work can be implemented for predicting cross-shore sediment transport models and beach evaluation models where reflective conditions exist.

SWASH MOTION DUE TO OBLIQUELY INCIDENT WAVES

A special reflecting wall 12 m long and 2.1 m high was built off the beach at Reggio Calabria, and 30 wave gauges were assembled before the wall and were connected to an electronic station on land. It was possible to observe the reflection of wind waves generated by a very stable wind over a fetch of 10 Km. The experiment aimed to verify the general closed solution for the wave group mechanics (Boccotti, 1988, 1989), for the special case of the wave reflection.Significant features on Wadden Sea wave climate are evaluated in respect of the state of the art. Main emphasis was laid on an analysis of the governing boundary conditions of local wave climate in island sheltered Wadden Sea areas with extensions being sufficient for local wind wave growth. Explanatory for significant wave heights a reliable parametrization of local wave climate has been evaluated by using generally available data of water level and wind measurements.

TIME VARYING TSUNAMI ATTENUATION ABILITY OF COASTAL FORESTS BASED ON FOREST GROWTH MODELS

The great tsunami off Sumatra Is., 2004 has led us to initiate research into a new aspect of coastal forests — their damage reduction capacity. Coastal shelterbelt plantation is a promising countermeasure to mitigate tsunami disaster, and possesses concurrent benefits for the coastal environment. This studys aim is to assess the tsunami attenuation ability of coastal forests by applying knowledge from forest science. The temporal developments of tree diameter and stand density under self-thinning conditions are discussed. An analytical formulation of the tsunami attenuation coefficient is developed based on forest growth models. Tree throw-down effect by tsunami attack is included, and the maximum tsunami attenuation is assessed in regards to the temporal development of the coastal forest. Furthermore, trunk diameter distributions are considered, and more realistic evaluations on tsunami attenuation ability of coastal forests are attained.

EFFECTS OF PARTICLE PROPERTIES ON OSCILLATORY SHEET-FLOW DYNAMICS

In order to reproduce intensive sediment transport over flat beds; the so-called sheet-flow in laboratories, a number of experimental studies using various kinds of artificial particles have been performed. However, no systematic discussion has been made concerning the effects of particle properties such as size, shape and material on the sheet flow dynamics. In this study, comprehensive analyses on existing data sets have been performed to examine the dynamical equivalence between sediment transport using natural sand and that using artificial particles. First, the mechanism through which particle properties affect sediment transport is discussed. Second, systematic data analyses are conducted on the transport properties in the light of particle properties.

Retrieval of missing values in water temperature series using a data-driven model

A measurement buoy with attached sensors has been deployed at our study area to monitor hydrodynamics, water properties, and water quality conditions. High-resolution temporal data have been collected and streamed into an online system that is accessible in nearly real-time. However, in certain circumstances the sensors may fail to provide continuous and high quality data. This results in gaps or corrupted values. The aim of this study was to reconstruct the faulty values. This paper proposes a method based on a data-driven model, using an Artificial Neural Network combined with a Genetic Algorithm to generate a synthetic data series. The generated data can be used as a patch for the incomplete measured data. Additional improvements were achieved by removing seasonal patterns from the original time series using a wavelet decomposition prior to the data-driven model training process. Comparisons with a standard missing-data imputation method using the Kohonen self-organizing map were made to further asses the performance of the proposed data-driven model. The algorithm was applied to water temperature data, but the same approach is applicable to other parameters of interest.

SEDIMENT TRANSPORT IN SWASH ZONE UNDER OBLIQUELY INCIDENT WAVES

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Measurements of Current Velocity Generated in Swash Zone by Obliquely Incident Waves

ABSTRACTLongshore current velocities due to obliquely incident waves have been measured by a tracer method in the swash zone including the landward region of the still water shoreline. Substantial longshore current velocity was detected in this region, although it is normally treated as zero in conventional time-averaged longshore current models. The magnitude of the velocity at the mean water shoreline increases with the swash zone width and shows good correlation with the surf similarity parameter.