1997 Fiscal Year Final Research Report Summary
Study on Algae Accumulation by Thermal-Siphon Action in A Eutrophic Stratified Reservoir
| Project/Area Number |
08650607
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (C)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
水工水理学
|
|---|
| Research Institution | Kobe University |
|---|
Principal Investigator |
ICHIOKU Kohji Dept.Architecture and Civil Engin., Kobe Univ., Associate Professor, 工学部, 助教授 (40127303)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
KANDA Tohru Dept.Architecture and Civil Engin., Kobe Univ., Professor, 工学部, 教授 (30029144)
|
|---|
| Project Period (FY) |
1996 – 1997
|
| Keywords | Reservoir Dynamics / Algae Bloom / Thermal Siphon / Buoyancy Flows / Eutrophication / Thermosolutal Convection / Internal Circulation / Double Diffusion |
|---|
| Research Abstract |
The thermal siphon is defined to be an internal gravity circulation generated by non-uniformity of temperature field in enclosed water areas. This is considered to be responsible for accumulation of algae in a certain location in lakes and reservoirs, which sometimes brings serious water quality troubles. The present research has been performed in order to find a relationship between the water mass transportation and the thermal siphon flows. It is expected that the finding in this problem would give us an insight into technical countermeasures to prevent water quality troubles.
A water quality measurement is performed in a reservoir, where a multi-density structure consisting of temperature and material concentrations is constructed. Cross-sectional profiles of temperature, electric conductivity and dissolved oxygen shows that chemical and biological reductions under anaerobic condition produce high concentration of dissolved materials along the reservoir bottom, which generates inclin
… More
ed plumes. Heat and dissolved materials are transported by this plume towards the deepest region of the reservoir. This might be a possible mechanism to produce an inverse temperature gradient and a very stable chemical strartification there. The field data suggest that non-uniformity not only of temperature but also of dissolved materials concentration is involved in generation of internal flow fields. Here, we refer this to be "a thermosolutal siphon" which significantly affects a double-density field of thermal and chemical stratification.
The thermosolutal siphon process was also investigated through a model testing in a simplified two-dimensional reservoir, where a bottom slope was installed and a constant flux of buoyancy was imposed on the water surface. The model experiment was carried out experimentally and numerically. Both of the tests showed that the thermosolutal siphon transported heat and mass very efficiently.
Through the field measurements and examination in the physical and numerical models, it was found that the thermal and thermosolutal siphon were the mechanism for integration and accumulation of nutrients, algae and other materials in a certain local area of a reservoir.
The next step we should take is to devise a countermeasure against water quality troubles in considering these results obtained in this research program. Less
|
-
-
-
-
-
-
-
-
-
[Publications] Kanda, T., Michioku, K., Nishikawa, T., Higashino, M,Itoh, T,Ishikawa, K.: "Field Survey on Water temperature and Quality in A Reservoir with Unstable Stratification in Its Bottom Layr" J.Hydroscience and Hydraulic Engineering. Vol.15, No.2. 41-48 (1997)
Description
「研究成果報告書概要(欧文)」より
-
-
[Publications] Michioku, K., Kanda, T., Itoh, T., Nishikawa, T., Ishikawa, K.and Higashino, M.: "Field Measurements of Water Quality in A Partially Overturning Reservoir with Inverse Temperature Gradient in Its Bottom Layr (in Japanese)" Proc.JSCE. No.572/II-40. 33-48 (1997)
Description
「研究成果報告書概要(欧文)」より
-
-
-
-
-
-
-
