Masamitsu Kuroiwa

APPLICABILITY OF A QUASI-THREE DIMENSIONAL NUMERICAL MODEL TO NEARSHORE CURRENTS

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

Effect of the Coastal Protection using the Beach Nourishment at Tottori Sand Dune Coast, JAPAN

ABSTRACT Shibutani, Y.; Kuroiwa, M.; and Matsubara, Y., 2016. Effect of the Coastal Protection using the Beach Nourishment at Tottori Sand Dune Coast, JAPAN., Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 695–699. Coconut Creek (Florida), ISSN 0749-0208. Beach erosion is a serious problem worldwide. The Tottori Sand Dune coast had started eroded in the 1950s, and the beach nourishment project has been carried out to restore the shoreline since 2005. The total volume of the sand was approximately 650,000 m3 from 2005 to 2014. In particular, a large amount of sediments, which was 100,000 m3, was injected in 2010 and 2011. In this study, the effect of the project was estimated. The sand volume increased temporarily after the large-scale beach nourishment, and then, the sand volume gradually decreased. However, the shorelines showed restoration trends after the beach nourishment project. In addition, although a part of the injected sediments was moved to the Tottori port, recovery of the shoreline was maintained.

Numerical Model for Predicting Sand Bar Formation around River Mouth

하구역의 지형변화를 예측하기 위해 3차원 해빈 변형 모델을 통한 계산이 수행되었다. 본 모델은 수심적분을 기초로 한 준 3차원 연안흐름 모듈로 구성되며, 해안선의 변화, 부유사의 이송-확산 효과를 고려할 수 있다. 우선 모델의 성능을 확인하기 위해 3차원 해빈 변화 모델이 하구역 사주 형성에 적용되었다. 다음으로 동해에 인접한 Ara 강 하구에 모델이 적용되었다. Ara 강의 사주의 동계 변화가 재현되었으며 계산결과는 현장 관측 결과와 좋은 일치를 나타냈다.

N-Line Model for Predicting Beach Evolution due to Nourished Sands

A numerical beach evolution model, which can predict depth contour line change due to beach nourishment, was proposed. The effect of beach nourishment was taken into account by solving two- dimensional advection diffusion equation for nourished sand material. Some model tests of beach evolution due to nourishment were performed. Furthermore, the new N-line model was applied to preservation of eroded beach using a sand recycle method measures, and then the performance of the model was investigated.

3D Morphodynamic Modeling of a Sand Recycling System

ABSTRACT Yasumoto, Y.; Kuroiwa, M.; Shibutani, Y.; Osakada, Y., and Matsubara, Y., 2016. 3D morphodynamic model for sand recycling system. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 502–506. Coconut Creek (Florida), ISSN 0749-0208. Sand nourishment such as sand bypassing or sand recycling is an effective measure against beach erosion as an alternative technique. The method for setting the optimum injecting amount, site and running cost has not been developed. A numerical model considering the sand nourishment is needed to evaluate the performance of the sand recycling and bypassing projects. This paper is concerned with the development of 3D beach evolution model for taking account the sand dredging and injection processes. In this paper, a model test for sand recycling in an area with artificial reefs was carried out. The model was applied to a sand recycling project conducted at a field site with five artificial reefs (an erosion area). The applicability against the morphodynamics around the five artificial reefs was investigated. Although the volume of erosion/deposition behind the artificial reefs was overestimated, the developed numerical model qualitatively agreed with the measured bathymetry.

Applicability of 3D Beach Evolution Model with Wave-current Interaction to River-mouth Bar Formation

ABSTRACT Kuroiwa, M.; Shibutani, Y.; Yasumoto,; Mase, H, and Matsubara, Y., 2016. Applicability of 3D beach evolution model with wave-current interaction to river-mouth bar formation. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 73–77. Coconut Creek (Florida), ISSN 0749-0208. A coastal area model with wave-current interaction was presented, and then the performance and applicability of the numerical to morphodynamics around river mouths due to waves, wave-induced currents and river flows were investigated. First, model tests were carried out under a variety of wave and river discharge conditions to investigate their capability of predicting the formation of sand spit and terrace topographies. Second, model verification using a field site was conducted and the applicability was investigated. From the computed results, it was confirmed that the prediction of presented model had good qualitative agreement with an actual sand spit formation.

A Facility Composed by Oyster Shell Filters for Purifying Contaminated Water in Closed Water Area

Various technologies are developed about the improvement of seawater property in the closed water such as the inner bay and lakes and marshes. The seawater exchange tends to stagnate in the closed water because flow is small. Therefore, even if the effective technology to the improvement of seawater property is set up, the effect becomes limited. Then, flow is cased by using the energy of the small-scale wind waves generated in the closed water, and it proposes effective use of the water quality purification. Additionally, the hydraulic model experiments and the numerical simulation of the facilities are executed, and the effectiveness is conformed.

Characteristics of Morphological change on the Sendai River Mouth in Tottori Prefecture

Field investigations at the Sendai River mouth in Tottori Prefecture were carried out in order to clarify characteristics of bottom topographical changes. Sounding surveys were carried out from Sept. 2004 to Oct. 2006. Morphodynamics around the Sendai River mouth were discussed using the results of the surveys. It was found that a sand bar due to wave action in winter season was formed in the river mouth and then the sand bar was flushed by a flood in rainy season or a typhoon. The amount of deposited and eroded sediments in the river mouth was also estimated. Furthermore, a numerical analysis was carried out using 3D morphodynamic model in order to clarify a qualitative relation among river discharges, wave conditions and morphodynamics.

A quasi-three dimensional numerical model of nearshore currents

This paper presents a quasi-three dimensional numerical model of wave-induced currents due to wave breaking so as to make it applicable to the coastal region with coastal structures and barred beachs. First, applicability of the present model to undertow velocity and nearshore current around the detached breakwater was investigated by comparing with the results of laboratory tests. Secondly, nearshore current on the barred beach was computed. Finally, nearshore current around the harbor in the field was computed and then the results of computation were compared with those of field observations.

Numerical Model of Dynamic Response of Flexible Floating Pier for Marina due to ocean waves

This study is concerned with the development of numerical model for the dynamic response of flexible floating pier due to ocean waves. The numerical model was induced by improving a numerical method for rigid floating structure. The motions and the tension forces of mooring lines of the pier were calculated from the method. The results of numerical simulation were compared with those of laboratory tests. It was found that the flexibility of the joints is a dominating parameter for the vertical movements the floating pier.