Makoto Ifuku

DEVELOPMENT OF EELGRASS(Zostera marina) BED UTILIZING SAND DRIFT CONTROL MATS

Field observation for the development of eelgrass(Zostera marina) beds was conducted off Kushiki beach, Naruto, Tokushima Prefecture. Chemical fiber mats were used to control the sand drift. Square seeds bags with side 30 cm long were laid under the mats in November and December 1995 and also in January 1996. In May 1996, the amount of eelgrass germinated per unit area reached up to 100/m2. The results of numerical analysis indicated that the velocity inside mat decreases when the velocity at the upper boundary becomes large. A small amount of circulating flow takes place with the occurrence of vertical flow, which seems to relate to the diffusion of suspended sediment. Sediment concentration near the bed, averaged over a wave period, is about 10 ~ 30% of that without mat. The seeding method presented in this study is demonstrated to be one effective means for the development of eelgrass beds.

The regional steady interface between fresh water and salt water in a coastal aquifer

Abstract First, a theoretical model is presented which is useful for determining the regional steady interface between fresh water and salt water under the appropriate boundary conditions for both confined and unconfined aquifers. This model is then applied to the confined groundwater in the estuary of the Naka River, Tokushima Prefecture, Japan, and the phenomenon of the seawater intrusion into the aquifer is analyzed. Boundary conditions of the confined aquifer and the parameters necessary for analysis are determined from the data. Calculations using a finite-element method are carried out in various cases, by changing the inflow S R or the total pumping amount Q of the groundwater in this alluvial plain. It is found that the region where salt water is intruding expands rapidly inland when S R approaches Q and vice versa. It is also found that the distributions of chloride ion concentration in groundwater calculated by this model with a simplified assumption are in fairly good agreement with the results observed in deep wells.

SUSPENDED SEDIMENT CONCENTRATION IN THE SURF ZONE

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.

Measurement of Flow and Topography Change Using ADCP around Hiji River Mouth

In this study, the flow and the topography change around the river-mouth bar are clarified by the measurement using ADCP. At the offshore side of river-mouth bar, the clockwise circulation is significant and the river-mouth bar advances toward the offshore. The growth rate of river-mouth bar is controlled by the sandy shoal which is formed at the terrace. After stopping the extraction of sediment at the offshore side of the river-mouth bar, the secular change of the sediment volume is approximately constant. Judging from this result, it is supposed that the sediment budget around the rivermouth bar is related to the extraction of sediment.

Dynamics of Suspended Solid in Hiji River Estuary

The present paper is composed of the field measurement in Hiji river estuary and the numerical simulation for suspended solid. In the field measurement, the turbidity maximum was not able to confirm. It was the reason that the rate of discharge due to rainfall is much during the measured period. The breakage of aggregate is modeled, that is, when the diameter of the aggregate is larger than the micro-scale by Kolmogorov and the drag force acted to the aggregate excesses the critical value, the aggregate splits into two equal fragments. In the numerical analysis, the temporal variation of suspended solid concentration agrees well with the measured results.

Evaluation on the Environmental Restoration Efforts of the Artificial Shoal installed inside of the Upright Breakwater

The artificial shoal area on the basis of ecosystem engineering has been appliedto the breakwater newly established at Mishima-Kawanoe Port, in Ehime Prefecture. The objective of this study is to evaluate how the target indicators established during the planning stage is achieved and to obtain ideas adopting to other environmental restoration projects relevant to port structure construction in future. The evaluation points of the ecosystem function are, 1) Index species appearing on the artificial shoal, 2) Reduction of organic carbon loaded from attached animals by various organisms activities. As a result, it is suggested that theecosystem is currentlyfunctioning well in the artificial shoal. Additionally, adaptive management concepts in developing the environmental restoration facilities are proposed.

Mobile Measurement of Tidal Current over Wide Area by ADCP and Behavior of Sand Wave in Bisanseto Fairway

In the present paper, the mobile measurement of tidal current was conducted by using the developed system with ADCP and D-GPS over the wide area in Bisanseto fairway. On the basis of the measurement, the sediment transport mechanism and the dynamics of sand wave formation is understood, and then, the fundamental information is obtained for the maintenance of the fairway. In the flood and ebb tides, the amplitude of tidal current in the upper layer is similar to it in the lower layer, but the current direction is slightly different near the deeper part.

Studies on the Salinization of Coastal Ground Water

In this paper, we first presenta theoretical model on the phenomena of these a water intrusion into coastal aquifers. Withthe use of this model, the spatial distribution of fresh and salt water interface in steady stateis easily determined either in the confined or unconfined aquifer which has arbitrary plane boundaries. We next apply this model to the confined ground wate rin the estuary of the Naka River, Tokushima Pref. The variation of spatial distribution of fresh and salt water interface is investigated in detail in connection with the changes in pumping amount or in inflow rate of ground water.