21. A Long Wave in the Vicinity of an Estuary [6]

In this paper, the long waves around the estuary are discussed for the RST wave in Section 3, the RD wave in Section 4, the secondary reflection in Section 5, the effect of the canal in Section 6, the effect of the corner of the estuary upon the diffracted wave from the other corner in Section 7, and the emitting point of the RD wave in Section 9. And further the secondary reflection of the diffracted wave around the single right-angled corner at the leeward coast is examined in Section 8. The conspicuous features exposed are as follows. (i) The lateral mode in the canal of the estuary is the greatest in intensity for kd=π (k: the wave number of the incident wave, d: the half width of the canal), the value of which amounts to about 0.5 (the amplitude of the incident wave is assumed as 1.0). (ii) When kd is small, the secondary reflection of the diffracted waves around the estuary are composed of two kinds of waves. One is the secondary reflection along the coast near the mouth of the estuary, directing to the open sea, and the other that along the bank of the canal near the mouth which is directed toward the inside of the canal. (iii) Among the secondarily reflected waves of the diffracted waves around the estuary, the secondary reflection from the bank of the canal directly behind the coast, in which the invading wave is diffracted toward the inside of the canal, is in intensity about four or five times the other secondary reflections.|本報告に論じられている内容は次のごとくである.第3節においてRST(合成)波,第4節においてRD(反射回折)波,第5節において2次的な反射,第6節において河口水路の影響,第7節において回折波に対する反対側の河口隅の影響,第9節においてRD波の出発点についての論で,以上はすべて河口近傍の長波についての論議である.更にまた,単一の直角隅角部の回折波の2次的反射が第8節において調べられている.得られた結論のうちで著しいことは次のごとくである.(i)河ロ水路の横モードはkd=π(k:進入波の波長,d:河口水路の幅の半分長)のときもっとも大きくなり(共鳴モードを意味する),その量は約0.5(進入波の振幅を1.0として)に達する.(ii)kd小さいとき,河口近傍における回折波の2次的反射波は2種類にわかれる.一つは河口近くの海岸において広海に反射する波,もう一つは水路の堤で水路内に反射する波である.(iii)河口近傍の回折波の2次的な反射波のうちで,回折波が回折をうけた海岸の直接背後の水路堤よりの2次反射は他の2次反射より大きく約4あるいは5倍に達する