Mikio Sasaki

THEORETICAL MODEL FOR NEARSHORE CIRCULATIONS

The Labrador Sea Extreme Waves Experiment (LEWEX), is an international basic research programme concerned with full-scale measurements, analysis, modelling and simulation in test basins of 3-dimensional seas. The research is carried out in order to assess the significance of 3-dimensional sea states in engineering applications. The first phase of the programme full scale wave measurements in the North Atlantic Ocean was performed at a site and time that had a high probability of encountering severe sea states. The present publication shows examples of measured bi-modal directional sea spectra obtained with the WAVESCAN buoy and directional sea spectra measured with an airborne Synthetic Aperture Radar (SAR). Directional spectra of gravity waves are obtained with the SAR both in open waters and below an ice cover. Further work is needed in order to verify SAR-measurements with in-situ observations. In-situ measured directional spectra are also compared with hindcast spectra from the 3G-WAM model. Hindcast significant wave heights were found to be lower than the in-situ measurements.The littoral drift model developed at DHI and ISVA, see Deigaard et al. (1986b) has been extended to include the effects of the irregularity of the waves, of a coastal current and a wind acting on the surf zone. Further, a mathematical model to simulate the near-shore current pattern along a barred coast with rip channels has been developed. The influence on the littoral drift of the irregularity of waves, wind, coastal current, and rip channels is discussed. It is concluded that irregularity of waves and presence of rip channels must be considered while coastal current and wind action are of minor importance.At present, the Prodhoe Bay oil field in Alaska contributes a substantial amount of the domestic oil production of the United States. Oil is also expected to be present on the continental shelf of Alaska, and it is estimated that approximatedly 28 percent of the total U. S. reserve is located beneath the shallow ice covered seas of the Alaskan continental shelf. To expolre and to exploit these oil rich resources, engineers are confronted with hostile oceanographic conditions such as high tides, waves, strong currents and sea ice. The same area is also rich in fishery resources. Being one of the most productive fishing grounds in the nothern Pacific, the potential ecological impact due to an oil spill is of a major concern. This paper describes the methologies used for the development of a modeling system for the oil risk analysis. The system is designed with generality in mind so it can be used for other coastal areas. The development of three dimensional models used in the modeling system described here have been published in the earlier International Coastal Engineering Conferences (Liu and Leendertse, 1982, 1984, 1986) and a report published recently by RAND (Liu and Leendertse, 1987). In the oil-spill risk analysis, these three dimensional hydrodynamic models are coupled to a two-dimensional stochastic weather model and an oil weathering model.The two projects (LUBIATOWO 79 and LUBIATOWO 86) were aimed at study pore pressure behaviour in natural sand bed in the coastal zone of the Baltic sea under the action of storm waves. During both projects, the wave induced pore pressures at the various levels in the sea bed were measured. The collected data were used to verify the applicability of the various theoretical approaches. In the conclusion, the range of the application of the particular analytical method is given.The rapid recession of the shingle bank of Hurst Beach (up to 3.5m/yr) makes it an excellent natural laboratory for the study of the factors which influence the stability of shingle beaches. Studies have included: the significance of long period, high energy, swell waves the classification and quantification of overwash processes run-up and seepage characteristics the effect of settlement of the underlying strata and the implications for practices in shingle nourishment. The studies have revealed the distinctive character of shingle beaches as compared with the more fully researched sand beaches. More detailed research on shingle beaches is justified particularly in relation to (i) the run-up characteristics including its interaction with swash cusps and (ii) the influence of the subsidiary sand fraction on the beach characteristics.Environmental assessment, engineering studies and designs were completed for a new 26.5 m3/s seawater intake system in the Persian Gulf. The original intake facility consisted of a curved, 60m breakwater with one end attached to the shoreline, a settling basin immediately adjacent to the shoreline and dredged to a maximum depth of approximately 5m, and a pumphouse structure located on shore such that the seaward wall formed one side of the settling basin. The facility located on an island in the Gulf, which served multiple seawater uses, had experienced both structural and operational problems, the latter consisting principally of excessive ingestion of sediment and seaweed. These factors plus the requirement for additional demands for seawater beyond plant capacity caused the owner to initiate a study of alternative intake systems, produce a design for the most effective solution and construct the new intake system.A two-dimensional wave prediction model suitable for use on personal computers is described. The model requires the twodimensional time-dependent wind field as input. Output consists of wave height, wave period, and wave direction estimates at all grid points on a computational grid representing an enclosed or semi-closed basin. Model predictions compare favorably with observations from a wave research tower in Lake Erie. A formula is provided to estimate how long a model simulation would take on a personal computer given the surface area of the computational domain, the grid size, and the computer clock speed.Cullera Bay is a neritic ecosystem placed on the Spanish Mediterranean Littoral largely influenced by the Jucar River, that brings about lower salinities than surrounding waters, and broad variations of its values. An extensive research, with 9 samplings throughout the year, was carried out, measuring both physical and chemical parameters, and the planktonic communities. The trophic status of the ecosystem, the spatial and temporal variations of the nutrients and the planktonic communities were studied, evaluating the influence of the river loads and the littoral dynamics. Some essential basis to allow a suitable emplacement of waste waters disposals along the Valencian littoral are set up in order to minimize the gradual eutrophication of this coast.In the last two years a whole of studies was realized in order to determine precise solutions to the regeneration of Villajoyosas beach, in the Spanish mediterranean coast. Investigations were carried out to the surrounding coastal areas based in field investigations and laboratory analyses of the beaches materials.

Velocity Profiles in Nearshore Circulation Current

ABSTRACTNearshore circulation current system on a plane beach produced by a uniform wave train, normally incident on the beach, is investigated experimentally. To measure mean rip and shoreward currents, a two-component electromagnetic flowmeter has been used on the beach. (1) The rip and shoreward currents near the break point gained a steady-state when the 8th wave reached the beach. The rip and shoreward currents in the region where the depth was twice breaker depth reached a steady- state at about 3 wave period later. When the currents gained the steady-state, the mean water levels reached always some constant levels. Currents in the upper layer of the flow region reached the beginning of the steady-state at about 2nd wave after currents in the middle and lower layers gained the steady-state. (2) Seaward currents over the total depth occurred in the rip current except on the surface near the break point. (3) The rip current velocities increased to a maximum value slightly offshore side of the break po...

Characteristics of Salt Water Movement in Iwaki River Estuary, Japan

The present study aims to investigate the characteristics of the motion of salt water and to show the temporal fluctuation of the vertical salinity distribution in Lake Jusan located in the estuary of Iwaki River in Aomori Prefecture, Japan. The Lake Jusan is the best productive water area of the shellfish, corbicula, in Japan in 2013. Then, the lake is very important in Aomori Prefecture as corbicula’s home. The change of the brackish environment influences the ecology of the corbicula shellfish, then, the shellfish harvest changes every year. Now, it is important to make clear the characteristics of the motion of salt water in the lake. In the present study, observations for the motion of the salt water going up to the lake and going down from the lake to the sea were carried out from June to September in 2015. The present study investigates the time change of the salinity distribution in a perpendicular direction and shows that the movement of the saltwater in the lake can be generated well by the theory given by Sasaki et al., 2009.

Shoreline Changes Around Artificial Headlands Along the Misawa Coast, Japan

Artificial headlands were constructed along the Misawa coast of Japan to prevent beach erosion caused by the construction of the Misawa fishery port in 1971. In order to assess the protection afforded by the artificial headlands, monitoring of shoreline changes was undertaken by conducting monthly GPS surveys and aerial photographs Based on the average position of the shorelines in 2006, advance of the shoreline has occurred along the coasts to the north and south of headlands B1, B3, and B11 The headlands B1 and B13 are in the south end and in the north end of the headlands group. Those lengths are 200 and 100 meters. The shorelines of the coasts to the north and south of headlands B5, B7 and B9 were stable, and the coast to the north of headland B13 was retreating. While the position of the shoreline along the north coast changes every month, change in the position of the averaged shoreline has decreased since the latter half of 2004. In conclusion, the artificial headlands were effective measures for countering beach erosion along the Misawa coast.

Characteristics of movement of solid particle in snow-water mixtures

In the present study, experimental observations for the movement of solid particles in the solid-water mixture flow were carried out in the horizontal pipe with a high-speed camera. When flow is slow, the picture was taken at 1000 scenes per second, and when flow is fast, the flow observation catches the solid particle very clearly at 4000 scenes per second. From the flow observation of the solid-water multi-phase flow that the solid specific gravity is near that of the transportation fluid, the change of the solid particle position and the speed change of the solid particle were shown in the present study. Within the scope of the present study, the following conclusions were derived. The solid particle flows with moving up and down. The change of the speed is large. The speeds in the lower layer and upper layer are both great fluctuations because the change of the speed near the wall is large. On the other hand, the vicinity of the solid particle in the middle layer of the pipe fluctuates a little and a steady speed continues. The solid particle near the wall rotates greatly, however, the solid particle in the middle layer of the pipe shows a small rotation. The rotation means that the flow of the mixtures is not Bingham flow.

Calculation of Water That Flows in River in North District, Japan

In this study, two models for snow and snowmelt were extended. Using those models, the calculation of water flowing in river was carried out. The results were compared with the observations. The outflow estimated by using the snow model in winter is in good agreement with the observations, and the snowmelt runoff predicted by using the snowmelt model in spring, April, May and June, is also at the good accuracy. The snowmelt runoff starts increasing from the early April, and it reaches the peak in the early May.Copyright

Energy Loss in Snow-Water Mixture Flow

Energy losses in the solid-water mixture flow where the density of solid is nearly equal to that of fluid were observed in horizontal pipelines. The observation was carried out to investigate the influence that the specific gravity of the solid particles exerted on the energy loss. A relative friction factor based on the friction factor of the pure water flow becomes larger as the solid concentration increases in the mixture flow of solid particles with the specific gravity 0.86 and 1.04. The relative friction factor is given with the Froude number, the solid concentration and the specific gravity of solid.Copyright

RIVER IMPROVEMENT WORK TO RESTORE BIOTOP AT JUNCTURE OF RIVERS

Recent days, many people are interested in natural environment of rivers. The Ministry of Construction have been attempting to preserve or to restore natural envioronment of rivers, since 1990 in Japan. In Tohoku district, river planning has been implemented to restore biotope in the Iwaki river which flows in Tugaru area at Aomori Pref. It gives educational chances to children and people who wantto meet living things in the river field. Considering the circumstances, this paper discriminates the following: preserving area, restoring area, watching living things area and digging to create shallow water area to expect to restore biotope.

ON THE EFFECTS OF CONCEPTION OF THE EXCAVATED CHANNEL ON FLOW VELOCITYIN THE INNER PART OF MUTSU BAY, ENVIRONMENT, AND GOODS MOVEMENT

The concept of the excavated channel at Shimokita arm is considered to increase the tidal exchange between the innerpart of the Mutsu Bay and the open sea.The change of flow velocity is calculated by FEM under two conditions with and without the excavated channel.In additions, the utilizing the excavated chamel as seaway gives the possibility of the reduction of carbon dioxide emission and energy consumption due to shortcut of seaway route.And, the possibility of reduction of goods movement cost is also investigated in the paper.

Characteristics of Salt Water Movement in Jyusan Lake

Observations for the movement of salt water were carried out in Jyusan Lake for two years from 1995. From this observations, we show the correlation between the flow velocity of stratified fluid and the generation and the disappear of salt wedge, and the motion of salt and fresh water in the lake. Then, we discuss the dynamics of salt water motion and the diffusion process of salt.