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Volume 56, Issue 4
Displaying 1-7 of 7 articles from this issue
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Kazuhisa CHIKITA, Koichi SAKATA, Shuji HINO1995 Volume 56 Issue 4 Pages 245-257
Published: October 30, 1995
Released on J-STAGE: December 11, 2009
JOURNAL FREE ACCESSDynamic behaviors of suspended sediment settling in volcanic Lake Kuttara, Hokkaido were examined by measuring the amount of trapped deposits and analyzing their particle size, biology, chemistry and mineralogy during a period from 14 September to 14 October 1989. The lake then was thermally stratified under conditions of the autumnal epilimnion cooling. The mean daily settling flux (g⋅m-2⋅d-1) of suspended sediment was numerically obtained from the amount of deposits trapped at five stations, and its horizontal distribution was successively described at depths of 15 m, 60 m and 100 m or 2 m above the bottom. About 50 to 60 vol.% of trapped sediment was occupied by endogenic phytoplankton (diatoms and dinoflagellates) and zooplankton (mainly, Bosmina longirostris), ranging over 11-125 μm in size. Its representative settling velocity is given as 1.26×10-5 m⋅sec-1, using the mean size of 32.6 μm and the mean particle density of 1, 034 kg⋅m-3. The spatial distributions of settling flux of sediment and a scale analysis of the sediment transport equation suggest that from the water surface to near the thermocline (15 m depth), the transport of settling sediment is controlled by vertically circulating flows due to a wind-forced surface wave, while below the thermocline (depths more than 15 m), it is decided by a secondary, vertically circulating flow due to rotating internal waves.View full abstractDownload PDF (787K) -
Makoto TANIGUCHI1995 Volume 56 Issue 4 Pages 261-267
Published: October 30, 1995
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSA long term measurement of the groundwater seepage rate has been made in Lake Biwa using an automatic seepage meter. The rate decreased from March to August, 1994, due to a decrease in the hydraulic gradient near the bottom of the lake caused by decreasing precipitation. Measurements of the groundwater seepage rate and the hydraulic gradient enable us to obtain the hydraulic conductivity of the aquifer beneath the lake.View full abstractDownload PDF (389K) -
Shuichi ENDOH, Miwa WATANABE, Hiroki NAGATA, Fumihito MARUO, Tetsuya K ...1995 Volume 56 Issue 4 Pages 269-278
Published: October 30, 1995
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSHorizontal distributions of wind over Lake Biwa have been measured almost simultaneously using three boats. Time changes in wind were also measured at several coastal points. These data, including AMeDAS and continuous records in Shiga Prefecture, were analyzed to find the characteristics of wind fields over and around Lake Biwa. Results show that the wind is not spatially uniform, and that the dominant strong northerly wind has a positive curl in the northern area of the lake and a negative curl in the south. This wind distribution is considered to be one of the most important maintenance mechanisms of the horizontal water circulation (gyres) often observed in Lake Biwa. This possibility is confirmed in part by numerical calculations with a simple two-layer circulation model.View full abstractDownload PDF (681K) -
Chunmeng JIAO, Michio KUMAGAI1995 Volume 56 Issue 4 Pages 279-289
Published: October 30, 1995
Released on J-STAGE: December 11, 2009
JOURNAL FREE ACCESSAn international program, the Biwako Transportation Experiment (BITEX'93), was executed in the summer of 1993. A current meter chain and a thermistor chain were then moored in the BITEX area. This permitted observations of the vertical dynamic and thermal structure of long internal waves and preceding internal fronts. After a strong typhoon, a marked depression of the thermocline appeared with an amplitude of 40 m which reached the lake bottom and induced a hypolimnion jet couple with a maximum velocity greater than 60 cm⋅sec-1. The correspondence between current speed and turbidity in the hypolimnion shows the possibility that sediment resuspension was generated by the event. Analyses indicated that this kind of V-shaped surge is due to the nonlinear long wave effect.View full abstractDownload PDF (635K) -
Tomoyasu FUJII, Setsuo OKUDA1995 Volume 56 Issue 4 Pages 291-296
Published: October 30, 1995
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSLake Nakaumi and the Sea of Japan are connected by Sakai Channel, while Lake Shinji and Lake Nakaumi are connected by Ohashi River, and temporal variations in water level of Lake Nakaumi and Lake Shinji are mutually related to the oceanic tide.
Then the characteristic and mechanism of their surface oscillation should be clarified as a system connected for the tidal oscillation. We constructed a simple linear model to get an analytical solution for surface oscillation in such a unique system, taking account of river inflows and water flux coefficient through water ways. We got a stationary oscillatory solution with a boundary condition of sine - type tidal oscilla-tion, and decided numerical parameters and coefficients by using in situ records of water level and water currents.
Numerical comparison between the results from our Connected Oscillation Theory and observed water levels shows an approximate accordance, but the numerical analysis is needed for more exact estimation of oscillation including wider ranges of amplitude and period of tide and river discharge.View full abstractDownload PDF (355K) -
Teruo ISHIDA1995 Volume 56 Issue 4 Pages 297-302
Published: October 30, 1995
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSCollections from floodplain waters on the Shiribetsu River basin, Hokkaido, northern Japan, yielded 1 species of calanoid, and each of 13 species of cyclopoid and harpacticoid copepods, respectively. Many individuals of Acanthodiaptomus pacificus were collected from a pond neighboring to farmland. Megacyclops sp. cf. magnus is recorded for the first time from Japan. The range of Attheyella byblis, known only from Honshu in Japan, is extended to Hokkaido. Females of Moraria terrula with male type caudal rami are reported. This type caudal rami are the first record for the genus.View full abstractDownload PDF (380K) -
Tomoyasu FUJII, Shingo NAGANAWA1995 Volume 56 Issue 4 Pages 303-307
Published: October 30, 1995
Released on J-STAGE: June 12, 2009
JOURNAL FREE ACCESSIn a brackish lake connected with an open sea through a narrow channel, the change in the lake water level is controlled by hydraulic characteristics of the channel and geometrical form of the lake, and some changes in the geometry of the channel or lake will bring about large effects on the water level change. Then if we have a plan for dredging or reclamation of the channel or lake, we have to estimate the change in the lake water level caused with the planned project in advance.
For the purpose of such planning, at first we have to get some approximate equations to connect the water flux rate through the channel with the water level difference between at both ends of the channel. From the past studies, we can use three kinds of relationship of water flux rate and water level difference as following.
(1) Simple linear correlation assumption between water flux rate and water level difference.
(2) Square root correlation derived from hydraulic theory.
(3) S-letter type empirical correlation at Ohashi River observed by ISHITOBI (1994).
We have compared the three numerical solutions of the changes in lake water levels which are calculated from the above three different correlations using the in situ record of water level changes in Lake Shinji and Lake Nakaumi, and our solutions have shown that three different correlations brought about almost same results of the calculated water level change if we select the appropriate water flux coefficient at the case of small amplitude of tidal oscillation.
Then we can estimate the water level change in brackish lakes approximately using the simplest linear correlation.View full abstractDownload PDF (327K)
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