Beach Processes of Shirarahama "a Pocket Beach"

The objective of this paper is to make clear the mechanics of sand transport in Shirarahama "a pocket beach" in order to study beach processes of stable, natural sandy beaches. Seasonal changes of the beach are caused by incoming waves and by blown sands, but a little beach erosion has gradually occurred due to a lack of beach sediment by recent urbanization of the hinterland. Characteristics of the change in the beach sediment are made clear, together with the present situation of the main sources of beach sediment. A method for the prediction of beach change by blown sands is proposed on the basis of both the law of sediment transport and the equation of continuity for beach changes. Changes in the distribution of longshore wave energy flux along the shoreline instead of the total rate of sand drift are considered for long-term and short-term beach changes. It is concluded from this that this beach is stable for most of the year, but the beach sediment may be transported in the offshore direction at the both ends of the pocket beach for a very short period by high waves associated with typhoons and monsoons

1990年代のインド洋ダイポールモードにおける大気海洋間相互作用の果たす役割の弱さについて

観測データと4次元結合同化システムの結果を用いて，インド洋ダイポールモード(IOD)発生時の東極の水温構造の変化を調べた．熱収支解析の結果，インドネシア沿岸域の水温偏差が湧昇の影響で変動している可能性が強まった．正のダイポール年において海上風偏差は全域で正偏差であったにも関わらず，沿岸域の海面熱フラックスが水温偏差を解消する方向に働いていた．これは沿岸湧昇による水温変動が潜熱フラックスに支配的に働いたためと考えられ，ダイポールモード発生時の実際の水温変動過程は領域平均の解析から得られた描像とは異なっている．IODの発生機構については，沿岸湧昇に加えて潜熱フラックスによって生じる海面水温偏差の重要性が特に指摘されてきたが，このような大気海洋が非断熱的に結合した正のフィードバック過程の働きは，従来考えられていたよりも弱い可能性が出てきたといえる．We analyze the temporal and spatial variation of the thermal structure of the eastern tropical Indian Ocean associated with Indian Ocean Dipole Mode (IOD), mainly using the water temperature of 10 years (1990-1999) of the World Ocean Circulation Experiment (WOCE) repeat IX1 expendable bathythermograph (XBT) section between Java and Western Australia together with the product of the air-sea coupled four-dimensional variational analysis (4D-VAR) system. The temperature anomaly of the XBT section reveals that the subsurface ocean temperature changes earlier than the surface before the surface IOD pattern starts to grow up. From May to August, a marked subsurface temperature anomaly is also found as well as the sea surface temperature (SST) that is formed primarily by the anomalous coastal upwelling along the south Java coast. Heat budget analysis along IX1 shows that the surface heat flux does not work to enhance the mixed layer temperature anomaly in the eastern pole region.観測データと4次元結合同化システムの結果を用いて，インド洋ダイポールモード(IOD)発生時の東極の水温構造の変化を調べた．熱収支解析の結果，インドネシア沿岸域の水温偏差が湧昇の影響で変動している可能性が強まった．正のダイポール年において海上風偏差は全域で正偏差であったにも関わらず，沿岸域の海面熱フラックスが水温偏差を解消する方向に働いていた．これは沿岸湧昇による水温変動が潜熱フラックスに支配的に働いたためと考えられ，ダイポールモード発生時の実際の水温変動過程は領域平均の解析から得られた描像とは異なっている．IODの発生機構については，沿岸湧昇に加えて潜熱フラックスによって生じる海面水温偏差の重要性が特に指摘されてきたが，このような大気海洋が非断熱的に結合した正のフィードバック過程の働きは，従来考えられていたよりも弱い可能性が出てきたといえる．We analyze the temporal and spatial variation of the thermal structure of the eastern tropical Indian Ocean associated with Indian Ocean Dipole Mode (IOD), mainly using the water temperature of 10 years (1990-1999) of the World Ocean Circulation Experiment (WOCE) repeat IX1 expendable bathythermograph (XBT) section between Java and Western Australia together with the product of the air-sea coupled four-dimensional variational analysis (4D-VAR) system. The temperature anomaly of the XBT section reveals that the subsurface ocean temperature changes earlier than the surface before the surface IOD pattern starts to grow up. From May to August, a marked subsurface temperature anomaly is also found as well as the sea surface temperature (SST) that is formed primarily by the anomalous coastal upwelling along the south Java coast. Heat budget analysis along IX1 shows that the surface heat flux does not work to enhance the mixed layer temperature anomaly in the eastern pole region

Eddy Correlation Measurements of Carbon Dioxide Flux over Coastal Sea Surface

The carbon dioxide flux over coastal seawater was measured by the eddy correlation technique at the Shirahama Oceanographic Tower Station of Kyoto University on August 23 and 24, 1994. The mean value of carbon dioxide fluxes measured is 0.10 mgm^-2 s^-1 with a standard deviation of 0.09 mgm^-2 s^-1. These upward fluxes are within ranges obtained over the Sea of Japan in 1986 and 1987. It is also noted that the present values of upward fluxes are about one tenth of the downward flux of carbon dioxide measured over actively growing paddy fields. Within a particular set of environmental conditions, the feasibility of applying the aerodynamic technique and the bulk technique to measuring the cabon dioxide flux over the ocean is demonstrated

山地・河川・海岸系における物質動態に関する研究(第4報)

流砂漂砂系において重要な役割を果たしている流体と堆積物の複雑な相互作用について、最近の進歩および課題を概観している。流域規模における降雨流出と土砂流出については、分布型モデルの進歩により、実問題の要請に応えられる精度での予測が可能となってきている。その実例として、インドネシア国Lesti流域における土砂管理や土地利用計画に繋がる研究成果を紹介している。水制等を活用した河川環境再生には、高精度かつマルチスケールの流水/土砂挙動の予測が必要になる。木津川流れ橋エリアの河川環境再生プロジェクトに関連して、最新の多次元流水/土砂挙動解析コードの適用例を簡潔に紹介している。さらに、海岸域における研究課題として以下のようなテーマをとりあげ、今後の研究の方向性について言及している： 漂砂系の土砂収支におよぼす海底谷の影響、イベント過程を見据えた岸沖方向の堆積物輸送の再評価、海浜環境のリモートセンシング、内湾―海峡―外洋系をつなぐ海水循環ダイナミクス、津波災害環境の復原に繋がる海域音波探査/堆積学的調査法のポテンシャル。This paper overviews some issues of complex fluid-sediment interactions that characterize the multi-scaled nature of sediment routing systems. It first demonstrates the capability of grid-based modelling for precipitation-derived processes of water flow and sediment transport in a hilly watershed (the Lesti River basin, Indonesia). The predicted and observed performances highlight the importance of vegetation cover in the sediment management that may relate closely to land-use practices. The paper then focuses on advanced numerical modelling for fluvial sediment dynamics, with particular reference to the reappraisal of groin systems in river restoration. There follows a concise discussion of the linkage between fluvial and littoral sediment delivery. Reviews are then directed on studies of coastal dynamical environments. The themes taken up include: the evolution of beach erosion such as occurring in Ogata coast; the coastal ocean dynamics pertaining to nutrient transport; and tsunami sedimentation - an attempt for exploring tsunami-induced submarine deposits.流砂漂砂系において重要な役割を果たしている流体と堆積物の複雑な相互作用について、最近の進歩および課題を概観している。流域規模における降雨流出と土砂流出については、分布型モデルの進歩により、実問題の要請に応えられる精度での予測が可能となってきている。その実例として、インドネシア国Lesti流域における土砂管理や土地利用計画に繋がる研究成果を紹介している。水制等を活用した河川環境再生には、高精度かつマルチスケールの流水/土砂挙動の予測が必要になる。木津川流れ橋エリアの河川環境再生プロジェクトに関連して、最新の多次元流水/土砂挙動解析コードの適用例を簡潔に紹介している。さらに、海岸域における研究課題として以下のようなテーマをとりあげ、今後の研究の方向性について言及している： 漂砂系の土砂収支におよぼす海底谷の影響、イベント過程を見据えた岸沖方向の堆積物輸送の再評価、海浜環境のリモートセンシング、内湾―海峡―外洋系をつなぐ海水循環ダイナミクス、津波災害環境の復原に繋がる海域音波探査/堆積学的調査法のポテンシャル。This paper overviews some issues of complex fluid-sediment interactions that characterize the multi-scaled nature of sediment routing systems. It first demonstrates the capability of grid-based modelling for precipitation-derived processes of water flow and sediment transport in a hilly watershed (the Lesti River basin, Indonesia). The predicted and observed performances highlight the importance of vegetation cover in the sediment management that may relate closely to land-use practices. The paper then focuses on advanced numerical modelling for fluvial sediment dynamics, with particular reference to the reappraisal of groin systems in river restoration. There follows a concise discussion of the linkage between fluvial and littoral sediment delivery. Reviews are then directed on studies of coastal dynamical environments. The themes taken up include: the evolution of beach erosion such as occurring in Ogata coast; the coastal ocean dynamics pertaining to nutrient transport; and tsunami sedimentation - an attempt for exploring tsunami-induced submarine deposits

山地・河川・海岸系における物質動態に関する研究

流域と沿岸域を繋ぐ流砂系のとらえ方について、最近の進歩を概観している。分布型流出モデルの実流域への適用と貯水池堆砂実績による検討例に基いて豪雨イベントによる土砂流出過程の重要性を指摘し、ついで、漂砂収支解析法の現況にふれ、沖合境界への堆積物流束、特にストーム条件下での堆積物流束の実態把握の重要性を指摘している。さらに、流体―堆積物系のダイナミクスに焦点を当て、土砂流出と河川生態系の関わりを示す現地観測、粘着性／非粘着性堆積物の混合体に対する流送モデルの提案、伝統的水制工による土砂制御機能の再評価、ならびに液状化堆積物の水中重力流れ機構の解明について論述している。This paper starts with an overview of recent developments pertaining to sediment routing systems that may connect fluvial, estuarine and coastal environments. It discusses sediment runoff analyses on a basin scale and methodologies for developing a budget of littoral sediment. It then focuses the discussion on recent findings obtained through collaborative research in the framework of a Center-of-Excellence program. The topics covered include the following: field observations of offshore-going sediment fluxes in the surf zone; reservoir sedimentation; an interrelationship between the riverbed morphology and habitat of a class of fish as influenced by sediment runoff; modeling of the transport of mixtures of non-cohesive and cohesive sediments with emphasis on wash load; reappraisal of traditional flow-control structures for river stabilization; and the dynamics of sediment gravity flows. Collectively, the coverage emphasizes the importance of addressing highly nonlinear fluid-sediment interactions.流域と沿岸域を繋ぐ流砂系のとらえ方について、最近の進歩を概観している。分布型流出モデルの実流域への適用と貯水池堆砂実績による検討例に基いて豪雨イベントによる土砂流出過程の重要性を指摘し、ついで、漂砂収支解析法の現況にふれ、沖合境界への堆積物流束、特にストーム条件下での堆積物流束の実態把握の重要性を指摘している。さらに、流体―堆積物系のダイナミクスに焦点を当て、土砂流出と河川生態系の関わりを示す現地観測、粘着性／非粘着性堆積物の混合体に対する流送モデルの提案、伝統的水制工による土砂制御機能の再評価、ならびに液状化堆積物の水中重力流れ機構の解明について論述している。This paper starts with an overview of recent developments pertaining to sediment routing systems that may connect fluvial, estuarine and coastal environments. It discusses sediment runoff analyses on a basin scale and methodologies for developing a budget of littoral sediment. It then focuses the discussion on recent findings obtained through collaborative research in the framework of a Center-of-Excellence program. The topics covered include the following: field observations of offshore-going sediment fluxes in the surf zone; reservoir sedimentation; an interrelationship between the riverbed morphology and habitat of a class of fish as influenced by sediment runoff; modeling of the transport of mixtures of non-cohesive and cohesive sediments with emphasis on wash load; reappraisal of traditional flow-control structures for river stabilization; and the dynamics of sediment gravity flows. Collectively, the coverage emphasizes the importance of addressing highly nonlinear fluid-sediment interactions

Evaluating the Variability of Sea-surface Wind Stress by the Combined of Eddy Correlation and Inertial Dissipation Methods

Field measurements of wind stress over the ocean surface were made at a sea observation tower by the combined use of the eddy correlation and inertial dissipation methods, which are referred to as \u22ECM\u22 and “IDM” hereafter, respectively. The values of the wind stresses obtained from both methods should agree well under ideal surface layer conditions. Thus, confirming the degrees of agreement between the stresses from ECM and IDM make it possible to reveal how air-sea momentum transfer varies depending on wave-field conditions. The present data show the degrees of agreement to depend significantly on the wave age in the case of pure windsea. This means that imbalance factors in the turbulent kinetic energy equation become large with increasing the wave age. Also, the degrees of agreement between ECM and IDM are found to vary with the deflection of the wind stress vector from the wind direction, which are caused by the presence of swell

渦相関－慣性散逸併用法に基づく海面風応力の変動特性に関する研究

Field measurements of wind stress over the ocean surface were made at a sea observation tower by the combined use of the eddy correlation and inertial dissipation methods, which are referred to as "ECM" and “IDM” hereafter, respectively. The values of the wind stresses obtained from both methods should agree well under ideal surface layer conditions. Thus, confirming the degrees of agreement between the stresses from ECM and IDM make it possible to reveal how air-sea momentum transfer varies depending on wave-field conditions. The present data show the degrees of agreement to depend significantly on the wave age in the case of pure windsea. This means that imbalance factors in the turbulent kinetic energy equation become large with increasing the wave age. Also, the degrees of agreement between ECM and IDM are found to vary with the deflection of the wind stress vector from the wind direction, which are caused by the presence of swell