1999 Fiscal Year Final Research Report Summary
Thermosolutal transport in reservoirs generated by release and leaching of salinity and nutrients from anaerobic bed
| Project/Area Number |
10650505
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
水工水理学
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| Research Institution | Kobe University |
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Principal Investigator |
MICHIOKU Kohji Dept. Architecture and Civil Engin., Kobe Univ., Associate Professor, 工学部, 助教授 (40127303)
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| Co-Investigator(Kenkyū-buntansha) |
MIYAMOTO Hitoshi Dept. Architecture and Civil Engin., Kobe Univ., Research Associate, 工学部, 助手 (50283867)
OONARI Hirofumi Dept. Civil Engin., Tokuyama Junior College, Professor, 教授 (30045041)
KANDA Tohru Dept. Architecture and Civil Engin., Kobe Univ., Professor, 工学部, 教授 (30029144)
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| Project Period (FY) |
1998 – 1999
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| Keywords | Reservoir Dynamics / Algae Bloom / Thermal Siphon / Buoyancy Flows / Eutrophication / Thermosolutal Convection / Internal Circulation / Double Diffusion |
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| Research Abstract |
In eutrophic reservoirs, high concentration of nutrients and ionic matters are released from the bed under badly anaerobic condition. Since the leaching process produces high salinity or heavy water mass on the bed, it gravitationally generates an inclined plume on the sloping bed and transport heat and mass to the bottom layer. This process may bring serious eutrophication of bottom water.
In order to predict heat and mass flux due to the thermosolutal transport and device a countermeasure against this, the following were examined. (1)Focusing on heat and salinity balance in the anaerobic bottom water, a water quality measurement was performed in a eutrophic reservoir. (2)Release flux of salinity from the bed was examined in an experimental model in which the bed materials sampled from the reservoir were installed in a tank and filled with anaerobic water. (3)Using a micro-bubble aerator system, an in-situ experiment of water purification was carried out. (4)A model experiment and an a
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nalysis on the inclined plume were performed in order to investigate buoyancy and flow fields.
The main findings are as follows. The thermosolutal convection is the main reason of making the reservoir bottom water to be extraordinary heavy and salty. Because of its very stable salinity stratification, the impounded water has never been overturned in the last many years. It makes the bottom water to be more seriously eutrophicated. It is the plume convection of warm water from the shallow layer to the bottom layer that is responsible for producing an inverse temperature stratification in the bottom layer. The heat and mass flux can be computed by the plume theory which was verified with the experimental data. The flux law was successfully applied for computing heat and salinity balance observed in the field survey. The micro-bubble aeration system was found to be very useful for promoting vertical mixing and aerating the bottom layer. After starting the aeration, the heavy and anaerobic bottom water mass was completely disappeared and the reservoir was fully overturned.
The next step we should take is to develop a prediction tool of water quality by considering the thermosolutal convection process. We should also continue the water purification experiment for improving the system to be of user-convenience. Less
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[Publications] Michioku,K., Kanda,T., Oonari,H., Nishikawa,T., Matsuo,K. and Kido,T.: "A preliminary experiment on reservoir water purification by using a micro-bubble aeration system (in Japanese)"Annual J. Hydraulic Engineering. Vol.44 (in print). (1999)
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