Akashi Strait Research Articles

Tidal exchange through Naruto, Akashi and Kitan Straits

In order to re-evaluate the water volume exchange through Naruto Strait, we have performed a numerical experiment (nonlinear barotropic model including the actual depth of water and the details of shoreline) where trajectories of a number of labeled particles are calculated during a full cycle of the M2 tidal current. The ratio of water volume exchanged through Naruto Strait to that through Akashi Strait is found to be twice as large as the previously estimated value. The calculated water exchange rate is 104 % for Naruto Strait, 52 % for Akashi Strait and 28 % for Kitan Strait. In the case where the tide-induced residual current is excluded from the calculated velocity field (i.e. considering only the M2 current), the calculated exchange rate maintains the level of 68 % for Naruto Strait, 18 % for Akashi Strait and 11 % for Kitan Strait, respectively. The mechanism of tidal exchange through these three straits is discussed, and it is shown that a suitable exchange rate is obtained by starting the calculation of trajectories of labeled particles at the time of either a maximum ebb- or flood-current.

明石海峡における船舶通航量予測のための基礎的研究(日本航海学会第45回講演会)

明石海峡における船舶通航量予測のための基礎的研究(日本航海学会第45回講演会)

播磨灘,大坂湾におけるChaetognatha,特に<i>Sagitta enflata</i>の分布について

Biological study of Chaetognatha has a considerably long history. Chaetognatha is im-portant macro zooplankton as indicator of water mass, and is considered to be playing an important role as the feed for fish. The present author had an opportunity to go through the Chaetognatha samples collected in the Harima-nada in the eastern part of Seto Inland Sea and in Osaka Bay from April, 1965 to March, 1966. The results obtained are as follows: 1) S. crassa was the most numerous species in the samples, and occurred nearly all through the year with maximum numbers in August. This species was numerically followed by S. enflata which appeared in great numbers in a period from September to December. S. bedoti and S. minima were the species which appeared sparsely in the samples, (See Table 1 and Fig. 2) 2) S. enflata was first seen in the beginning of July in 1965 in the southern part of Osaka Bay, and from that time on this species extended its distribution area northward in the bay. Up to the beginning of September the distribution front reached as far as the center part of the Harima-nada through Akashi Strait. After showing a little more expansion toward December, the population indicated falling tendency in January, and finally disappeared from the area in February. (See Fig. 3) 3) In the Harima-nada and Osaka Bay S. enflata was distributed mainly in the area with transparency of 5 to 10m. and seemed to be densely populated in the area of great transparen-cy. While no specimen was collected in the water mass with its transparency being less than 2m. (See Fig. 5)

明石海峡通航船舶の霧中における行動の実態(日本航海学会第34回講演会)

明石海峡通航船舶の霧中における行動の実態(日本航海学会第34回講演会)

Current Survey by Use of Air Photographs (Part 1)

The conventional method for measuring tidal current velocity generally employs current meters suspended, at predetermined depth, from buoys located at limited number of selected locations. Recently in Japan, the high industrial development and rapid harbour construction have brought demands for more detailed and synoptic surveys of current in straits and harbours. The aerial photogrammetric measurement of tidal current, adopted by the Coast and Geodetic Survey, U. S. A., for the first time, have given us some useful hints for our own development in tidal current measurement, which in turn gives answer to the above mentioned demands. This paper reports the principles and methods of photogrammetric measurement of tidal current survey, and the new techniques such as synchronized photography and vector analysis, developed by the authers. In next paper (part II), the results obtained by these methods applicated to Akashi Seto (Akashi strait), Japan will be reported.

A THEORETICAL INVESTIGATION ON AERODYNAMIC STABILITY OF LONG-SPANNED SUSPENSION BRIDGE

This paper presents a theoretical consideration on the flutter wind velocity taking into an account the various structural parameters on the base of the theory developed by F. Bleich, which is originally concerned with the twodimensional air stream. We investigate here, to some extent, a few fundamental cases of the three dimensional wind velocity variations in the horizontal direction and its influence on the critical wind speed. Numerical illustrations are proceeded for the 1st plan of the proposed Akashi Straits Bridge and compared with the results by A. Selberg's empirical formula for corresponding torsional and deflectional characteristics of the proposed suspension bridge.

明石海峡における船舶交通の実態調査結果(日本航海学会第31回講演会)

明石海峡における船舶交通の実態調査結果(日本航海学会第31回講演会)

明石海峡における船舶交通の実態調査方法(日本航海学会第29回講演会)

The paper describes on a method of the investigation into the actual condition for routing traffic in the Akashi Strait that the excution are under way for the Cross Channel Bridge Scheme. And we are recording the flow of shipping and the fishing activities in the strait by means of the Radar Photogragh and the Obsrevers Sketch.

Contour Map of the Upper Surface of Basement Rocks under the Sea-floor of the Akashi Straits

Japanese National Railways has been carried out a Series of submarine geological surveys at the Akashi Straits where interisland-through rail-and road-way are proposed. According to the results hitherto obtai.ned, there develop widely gravellous formations (from latest-Tertiary to earliest-Quaternary) underlain by Miocene group (mainly sandstone with some shale and conglomerate) or older granite.So, the author presents an every-5m countour map of these underlying groups based on Sparkers records. By this map (Fig. 3), thickness of the gravellous beds and relief of. basement rocks are numerically illustrated, and its accuracy is thought to within±5meters examined from all the standpoints of concerning factors.

STUDIES ON ECONOMIC DEVELOPMENT OF SHIKOKU REGION FROM THE STANDPOINT OF CONSTRUCTION OF BRIDGE OVER AKASHI STRAIT

It is the most important to construct the bridge over the Akashi Strait to enhance the industrial structure of the Shikoku Region, which will further tie the Hanshin Metropolitan Region in with the Shikoku Region as Hanshin's vast hinterland in Western Japan, and will improve the circulation of goods and people within that great region.The authors dealt with the future economic plan of the Shikoku Region from the viewpoint of the construction of bridge over the Akashi Strait. Therefore, a so-called Regional Input-Output Model Analysis and an Econometric Model Analysis were introduced to predict the economic structure of the Shikoku Region.In order to calculate the increment of total output in the Shikoku Region to comply with structural change of interregional trade in the Econometric Model Analysis, due to the construction of the Bridge, interregional shipment and importation of goods and services were set as exogenous variables.Through the above procedure, it was made clear that the construction of bridge over the Akashi strait was very efficient to economic development of the Shikoku Region.

On the Investigation of Beach Erosion along the North Coast of Akashi Strait

SynopsisSandy beaches are defensive zones created by nature, protecting the land against aggressive oceanic forces. They are very flexible and their configulations are varying daily, seasonally and annually, depending on many factors, such as wave characteristics, beach materials, shore structures and the others. The investigation of beach erosion is one of the most important and difficult subjects in coastal engineering.In this paper, a method for investigating the mechanism of beach erosion is presented, concerning the investigation practice of beach erosion along the north coast of the Akashi Strait, and the author's opinion of the following three subjects to be investigated is described:(a) Distribution of sand drift along the coast,(b) Distribution of sand drift along the beach profile, and(c) General characteristics of sand drift, suCh-as the type of sediment transport, the direction of drift and the others.