Lake Current in the Surface layer during Thermal Stratification on Shibere Lake, Yamanashi Prefecture, Japan YANG, Heakun* and Tadashi ARAI** Abstract : In this research, the primary factors affected to the formation of lake current of surface layer and thermal stratification of temperate lake have been analyzed, the daily change of water temperature, relationship with lake current and the research about the elements of meteorological phenomenon have been implemented. As a result, the lake current of surface layer occurring while the period of thermal stratification is showing the proportional difference of water temperature, thermal exchange caused by this has been known as the main energy source, and this is, secondly, considering as the interaction of the wind driven current by the prevailing wind. On the other hand, during the night time when the water surface is cooled, and it is considering as the vertical convection is occurring than horizontal circumfluence. Also, there exists the water mass, which is circumfluent counterclockwise and clockwise direction separately. The prevailing wind is rather affected to the moving direction and moving speed of water mass, but it doesn t affect to the whole flowing direction. Key Words : thermal stratification, lake current, surface layer, Shibere Lake, SiteBuilder 3D (Researcher, Honam Culture Research Center, Chonnam National Univ.), yanghk@chonnam.ac.kr (Professor, Faculty of Geo-Environmental Science, Rissho Univ., Japan) 145
양해근ㆍ新井 正 1974 등) 등을 중심으로 많은 연구 성과가 발표되 었다. 그리고 온대호소의 성층현상에 대해서는 吉 村(1928, 1933, 1937)와 新井(1962, 1964) 등을 중심 으로 활발한 연구가 진행되었으며, Dake and Harleman(1969), Henderson(1976), 新井 외(1985), Kim(1995) 등에 의해 호류와 오염물질 확산간의 상호작용에 대해도 연구되었다. 그러나 수온성층이 강화된 여름철에도 표수층은 바람에 의한 교란과 증발, 기온의 일교차의 영향으 로 소규모 대류현상이 일어나지만(新井, 2000), 이 러한 대류현상은 그 규모가 매우 작고, 표면부에 한정된 현상이라는 점에서 그 동안 주목을 받지 못했다. 또한 표면부의 열적교류에 의한 소규모 대 류현상은 여름철 호소의 수질환경 특히 조류증식 과 그 규모를 결정하는 주요 요인 중의 하나임에 틀림이 없다. 따라서 본 연구에서는 이러한 점에 연구의 중요 성을 인식하고, 인위적인 물관리가 배제된 자연호 인 시비레(四尾連)호를 대상으로 표수층의 호류형 성에 영향을 미치는 요인을 분석하고, 그 성인을 밝히기 위해 호수 수온의 일변화와 호류와 관계, 그리고 기상 요소(풍향 풍속 등)를 중심으로 관 측을 실시하였다. 2. 연구지역의 개관 시비레(四尾連)호는 일본 야마나시(山梨)현 죠 후(甲府)분지의 남남서방향으로 약 17km 떨어진 미사카(御坂)산지의 서쪽 산정부근에 위치한 작은 Figure 1. 3D model of the study area by Kashimiru 3D and ArcView GIS Software 146
j Figure 2. Location of the observation sites in Shibire Lake. : waster temp. and water quality, : data logger of water temp., : current meter, pranometer and net pyrradiometer, : anemometer 147
Figure 3. Vertical distribution of WT(water temp.), DO, ph and EC at center point(st.4) in Shibire Lake (9:00, am. Aug. 03, 2001) 148
Figure 4. Daily temperature profiles and isopleths in 2-3 Aug. 2001. µ µ 149
(a) measured from 6 to 7 p.m., in Aug. 02. 2001 (b) measured from 4 to 5 p.m., in Aug. 03. 2001 Figure 5. The surface temperature of water by infrared thermometer. The average wind speed at (a) and (b) was recorded up to 1.0~1.5 and 1.1~1.2meters respectively. 150
Figure 6. Lake current was investigated by current drag. 151
Figure 7. Result of the observation of surface water temperature. 152
C C Figure 8. The sectional diagram of water temperature. 153
Figure 9. Variation of vertical water velocity(uscm: Ultra-Sonic Current Meter), wind velocity and water temperature at 0.5m and 1.5m depth. 154
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