報告書番号

U93027

タイトル（和文）

水産増殖への利用も考慮した潜堤付き防波堤の水理特性

タイトル（英文）

HYDRAULIC CHARACTERISTICS OF COMPOSITE BREAKWATER WITH DETACHED SUBMERGED MOUND FOR COASTAL NURSERY GROUNDS

概要 （図表や脚注は「報告書全文」に掲載しております）

当所では，従来の消波ブロック被覆混成堤を改良した新しい防波堤を開発している。この防波堤は混成堤および消波ブロックの転用で作る潜堤から成り，その防波堤周辺の水産資源の涵養を目指すものである。本報告は潜堤付き防波堤による港内静穏度および港外の流れを水理模型実験により把握し，従来の防波堤と比較するものである。主な結果は，次の通りである。（１）潜堤幅が有義波長の約１／１５，潜堤高が水深の７割を有する潜堤付き防波堤による港内外の波高比や反射率は消波堤の場合より小さい。（２）港内外の波高比，混成堤に作用する波圧などの観点から，混成堤と潜堤による波高低減水域の離間距離は設計有義波の約１波長程度が妥当と考えられる。（３）潜堤付き防波堤は潜堤の長さや開口長さを変えることによって，波高低減水域の流速を低減し，循環流を発生させることができる。以上の結果により，潜堤付き防波堤の波高低減水域は水産資源の涵養に役立つ

概要 （英文）

WE INVESTIGATED METHODS FOR MAKING MORE EFFECTIVE AND ENVIRONMENT-CONSUIONS USE OF COASTAL STRUCTURES,AND FLOWS INDUCED BY COOLING WATER INTAKE AND DISCHARGE FOR 4 YEARS. ONE RESULT IS ANEW TYPE OF BREAKWATER WHICH IS EFFECTIVE FOR CREAKING COASTAL NURSERIES FOR FISH SHELL FISH. IN RECENT YEARS,A NUMBER OF COMPOSITE BREAKWATERS WITH CONCRETE ARMOR BLOCKS PILED JUST IN FRONT HAVE BEEN CONSTRUCTED.THESE SUPPRESS WAVE PRESSURE ON THE CAISSON AND WAVE REFLECTION.THE NEW TYPE IS A COMPOSITE BREAKWATER;IT IS A CAISSON A RUBBLE-MOUND TYPE WITH A DETACHED SUBMERGED MOUND OF ARMOR UNITS JUST IN FRONT OF THE CAISSON.THE HYDRAULIC CHARACTERISTICS WERE INVESTIGATED WITH TWO-AND THREE-DIMENSIONAL HYDRAULIC MODELS. THE MAIN RESULTS ARE AS FOLLOWS:(1)FOR SUBMERGED MOUND 1/15 AS WIDE AS THE SIGNIFICANT WAVE LENGTH AT THE TOP,AND70% AS HIGH AS THE WATER DEPTH,WAVE HEIGHTS JUST IN FRONT OF AND BEHIND THE CAISSON ARE LOWER THAN THOSE FOR CONVENTIONAL COMPOSITE BREAKWATERS WITH A FRONT PILE OF ARMOR BLOCKS WITH THE SOME VOLUME AS THE MOUND.(2)JUDGING FROM THE TRANQUILITY BEHIND AND WAVE FORCES EXERTED ON THE CAISSON,THE SUBMERGED MOUND SHAULD BE LOCATE ONE SIGNIFICANT WAVE LENGTHFROM THE CAISSON.(3)THREE-DIMENSIONAL MODEL TESTS OF THE NEW BREAKWATER WITH DISCONTINUOUS DETACHED MOUNDS SHOW THAT CURRENTS ALONG BREAKWATERS ARE RESUCED AND SEVERAL COUPLES OF CIRCULATING FLOWS OCCUR BETWEEN THE BREAKWATER AND SUBMERGED MOUNDS DURING A STORM.THUS,THE EFFECT OF CURRENT SWEEPING AWAY FISH EGGS AND LARVAE FROM AROUND BREAKWATERS IS SMALLER WITH THE NEW BREAKWATERS.THIS NEW BREAKWATER MORE STABLE ENVIRONMENT THAT IS FAVORABLE TO MARINE FISHERY RESOURCES.

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