河口沿岸海域の微細海況

村上, 彰男

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河口沿岸海域の微細海況

https://fra.repo.nii.ac.jp/records/2003384

Item type

紀要論文 / Departmental Bulletin Paper(1)

公開日

2024-04-25

タイトル

河口沿岸海域の微細海況

言語

タイトル

MICRO-OCEANOGRAPHY IN ESTUARY

言語

jpn

資源タイプ

資源タイプ識別子

http://purl.org/coar/resource_type/c_6501

資源タイプ

departmental bulletin paper

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metadata only access

アクセス権URI

http://purl.org/coar/access_right/c_14cb

著者

村上, 彰男

抄録

内容記述タイプ

Abstract

内容記述

1. Scope of work. As a rule, the sea condition of coastal waters is more complicated than that of the open sea. Especially in an estuary, variations are very considerable owing to the effects of complicated topography, wind, tide, river discharge, etc. On the other hand, clarification of the detailed sea conditions of coastal waters is urgently required for the benefit of fisheries, public works, industrial development and urban life. From 1964 through 1966, the Science and Technology Agency conducted an integrated study of coastal sea conditions in Hiroshima Bay with the Maritime Safety Agency, the Fisheries Agency and the Meteorological Agency as the participants. The author took part of this study and carried out a study concerning the mechanism of the exchange between the fresh and sea waters. An unique automatic observatory was designed for this purpose and installed near the estuary of the Öta River. The characters and movements of fresh, brackish and sea water masses were studied by means of this observatory and by supplemental observations. The automatic observatory takes measurements at several depths between the surface and the bottom of the sea at regular time intervals. Such method of automatic observation is the first attempt in Japan. The measured items are air temperature, wind direction and force, water temperature, electric conductivity, and direction and speed of current. The detectors for these elements are moved up and down through the water column by the motor installed on a tower. The tower is lccated at a point 250 m off the shore and 8 m in depth. Self-regulating and recording parts are placed in a house on land. The distance of about 300 m between the house and the tower is connected with a submarine cable. The observatory takes measurements at the water surface and then at 0.5, 1, 2, 3, 5 and 6 m below surface, and it takes about 10 minutes to complete one series of observation. Such a series is repeated every 30 minutes. The observatory began recording the data in January 1966, and was kept in operation until April 1968. Electric power was obtained from the commercial power supply. To avoid obstructing navigation, the tower was placed about 500 m to the east of the river mouth. The supplemental observations were carried out monthly from April 1966 to March 1967, and consisted of stationary and cruising observations. In the stationary observation, the same observation items as covered by the automatic observatory were continuously measured for 24 hours from a survey ship anchored at the river mouth. During the same period the cruising observation was carried out by another survey ship which made the round tour to cccupy the 10 stations located within 2 km of the shore. It took 2 hours to make a round, and four or five successive rounds were made. 2. Results obtained. (1). Thermal stratification occurs in two seasons of the year, namely, from April through September and from January through February. Vertical gradient of water temperature is 0.7 and 0.3℃/m respectively in the two seasons. Stratification occurs also when low-salinity water temporarily occupies the surface layer; in such a case, there is considerable difference between the surface layer and the underlying layer not only in temperature and electric conductivity but also in current pattern. (2). The discharge of the Ota River is abundant from March through July (with the maximum in July) and scanty from August through February (with the minimum in November). Needless to say, the sea condition of an estuary is ruled mainly by river discharge. Judging from the current velocity and chlorinity of the surface layer, however, it is only in. the period of abundant river discharge (i. e., above the year-round average) that the river discharge strongly affects the sea condition. (3). The sea condition of an estuary is affected by the tidal range as well as by river discharge. In the estuary of the Ota River the maximum tidal range is about 4 m and the tidal mixing of fresh and sea waters is not so intense ...... limited only to the upper layer ...... as in the estuary of the Chikugo River which is located in the inner part of the Ariake Sea and where the maximum tidal range measures 6 m. Spatial distribution of low-salinity water differs in the stratifying and the circulating seasons because of the different mixing conditions. (4). When tidal range is small or when river discharge is very large, the surface water flows down the estuary even during the flood tide and, consequently, there can be seen at a depth of 1 to 2 m a sharp discontinuity between the offshore-flowing low-salinity upper water and the underlying high-salinity water flowing ashore. The thickness of the former water varies with the river discharge :it is usually less than 2 m and sometimes only 20 to 30 cm. Such surface water is several per mil lower in chlorinity than the underlying water. 3. Problems pointed out. (1). As this was the first attempt to descend and ascend the detectors at an automatic observatory, the elevator apparatus went out of order rather frequently. The majority of the troubles was due to the increased friction or weight or to the clogging of the pores of detectors, which were altogether caused by the attachment of sessile organisms. The observatory composed of sea and land parts proved to be advantageous in the maintenance of the instruments and in securing the electric power. If all the parts are to be installed in the sea, it seems more desirable in the coastal waters to submerge them to the sea bottom than to float them by means of a bouy. (2). Since some of the hydrographic elements show sharp vertical gradients in an estuary, it is necessary to get a fixed point in the sea for their measurement. Particularly in the measurement of water current, the errors due to the rolling and pitching of the survey ship cannot be disregarded. In measuring the movement of a water mass, it is more desirable to follow a current float than to use a current meter. (3). The electric conductivity meter has to be improved so as to be adjusted more rapidly and surely, if it is to be used in an estuary. In the region of low salinities the relationship between electric conductivity and chlorinity is not the same as in the open sea, and the calibration curve must be drawn for each series of observation by securing a few water samples and determining their chlorinities by titration.

言語

bibliographic_information

ja : 南西海区水産研究所研究報告
en : Bulletin of the Nansei Regional Fisheries Research Laboratory

巻 1, p. 15-62, ページ数 48, 発行日 1969-03

出版者

南西海区水産研究所

言語

出版者

Nansei Regional Fisheries Research Laboratory

言語

item_10002_source_id_9

収録物識別子タイプ

PISSN

収録物識別子

0388-841X

item_10002_source_id_11

収録物識別子タイプ

NCID

収録物識別子

AN00181988

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