Ken-ichi Hirayama

A NEW PARAMETER FOR WAVE BREAKING WITH OPPOSING CURRENT ON SLOPING SEA BED

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.

OBSERVATION OF SNOWFALL BY RADAR RAFNGAUGE

To utilize data of Radar rain gauge in prediction for snowfall disttibution a model was proposed In this model, a calculation of wind field on arbitrary terrain is included. The accuracy of the prediction model are examined by comparisons with field data of hourly measurements of snow fall at seven sites, maximum snow depth distribution in dam depth basin and dam inflow.

Study on Rainfall Runoff Prediction System for Radar Raingauge

Radar rainfall gauge gives a better information of rainfall distribution than the conventional Thiesen method. In the present study, a system for the prediction of rainfall-runoff is constructed. This system includes packages to obtain a channel network from the digital map, to combine the radar rainfall information with the channel network, and to calculate the runoff using the kinematic wave model.This paper described the each package of the system. And parameters of the kinematic wave model were obtained for 20 runoff events in 1990 and 91. Application of this rainfall runoff prediction system to dam reservoiurs is possible with several minor improvements of the system.

Use of digital map for a radar rainfall-runoff model

When a radar rainfall information is available, the distributed rainfall-runoff model should be used. However a construction of the model includes a tedious procedure to construct a channel network from many corresponding maps.In this study a method to obtain the channel network automatically from the digital map based on simple principles is proposed. Then a distribution of radar rainfall can be supperimposed on this channel network to calculate the run-off by the kinematic wave model.Thus a distributed radar rainfall-runoff model could be easily established in any river basins.

Caluculation of Ice Cover Roughness from Velocity Distributions

Field measurements of velocity profiles for ice-covered streams were performed in Hokkaido. Surface conditions of the cover were classified into smooth ice cover, rippled ice cover and cover with frazil slush. Adaptability of logarithmic velocity distribution was first investigated. The friction factor fi and Mannings roughness coefficient ni were caluculated based on an assumption of the logarithmic distribution; average values ni for smooth and rippled cover were 0.012 and 0.021 respectively.

Calculation of Snow-melt Runoff to Three Dam Reservoirs of Kitakaii River

Calculation of snow-melt runoff to Shijyu-shida, Gosyo and Yuda dam reservoirs was performed. This numerical model requires only daily air temperature and precipitation at a representative point in the basin as input data. 8 parameters in the model were chosen from past meteorological and hydrological data, and calculated hydrographs show a good coincidence with observed runoff at these dams. Improvement of methods to determine these parameters is left for the future research.

Prediction of Snowfall Distribution Considering Effect of Wind

A numerical model is proposed to predict the distribution of snowfall considering the effect of snow transportation by winds. This model consists of;(1) calculation of wind velocity vectors (3-D potential flow) over an arbitrary terrain (using Digital Terrain Data), and (2) calculation of snow particle transportation by wind. Influences of parameters in the model on numerical results are examined and reasonable values for the parameters are selected. Based on the above model, several examples of snowfall distributions on the ground are obtained from the distribution of snow particles observed at 2000 m above the ground by a radar rainrauge.