Analysis of the convective mixing characteristics
Of estuarine reservoir by landsat tm images
When the inflow of fresh water is increased, the salinity decreases because the mixed salt water with inflow is drained through gates. On the contrary, if the inflow is reduced, the salinity rises by the intrusion of seawater from sea dike and outlet gate, and moreover, the salt water under density interface is also diffused and mixed into upper fresh water layer by density currents. Therefore, it is regarded that the convective phenomenon of inflow affects largely water quality in the freshening process of estuarine reservoir.
5.2 Convective Characteristics of flows
This study was used a numerical scheme based on finite difference method with general curvilinear coordinate system, and was carried out two-dimensional numerical simulation to analyze the convective mixing characteristics of flows in the freshening process. Fig. 2 shows the boundary extracted from TM image and the computational grids generated by adopting the multi-block grid generating method which the inlets (Q1-Q8) were divided into eight places for watershed and outlet (Qg) was fixed in the outlet gate of Yongam lake, respectively. Fig. 3 shows velocity-vector distribution simulated for 24 hours in the conditions (a) without (?t:2) and (b) with (?t:1) the inflow of fresh water and the open of outlet gate.
Fig. 2 Boundary of the Study Area Extracted from TM Image and Computational Grids
Fig. 3 Velocity-Vector Distribution in Conditions (a) without ( t=24h, ?t:2, Vmax=0.030 m/s)
and (b) with ( t=24h, ?t:1, Vmax=0.113 m/s) Desalted Fresh Water
Fig. 4 Classification Images of TM Data Acquired on (a) Sep. 22, 1992 and (b) Sep. 28, 1994
The results indicate that occur the large and small eddies in the most places of Yongam lake including the central part of lake, near outlet gate, and the outlet of link canal. The Eddies affect the convection and rotation of flows, which also accelerate the desalinization of stagnated salt water under density interface. Thus, it was confirmed that the convective mixing mechanism plays an important role in freshening process
5.3 Mixing Patterns in Freshening Process
Fig. 4 is the images classified using TM data of (a) Sep. 22, 1992 and (b) Sep. 28, 1994, respectively, which clearly shows the different patterns of estuarine reservoir, tideland, and seawater. The convective mixing patterns in freshening reservoir seems to be connected with complicated factors such as a suspended matter and its density, eddies related to inflow velocity, inflow discharge, the diffusion and mixing of density currents, and meteorological parameters et al.. The TM image data as shown in Fig. 4 can be applied to the works on the mixing patterns of convective flows on the surface of water and the environmental changes of tideland (or reclaimed land) changed according to the progress of reclamation projects.
6. Conclusion
The application with satellite image data and numerical analysis in the field of hydraulic engineering, which is considered as a useful way to analyze various hydraulic problems. Finally, it will be supplemented on the presentation for contents have not explained relating to atmospheric correction.
References
Baban, S. M. J., 1997. Environmental Monitoring of Estuaries; Estimating and Mapping Various Environmental Indicators in Breydon Water Estuary, U.K., Using Landsat TM Imagery. Estuarine, Coastal and Shelf Science, 44, pp. 589-598.
Choi, M. and Hoshi, T., 2000. Analysis on the Freshening Process of Freshening Reservoir by Desalt Fresh Water, Annual Journal of Hydraulic Engineering, JSCE, 44, pp. 1251-1256.
Torii, K. and Hoshi, T. et al., 1996. Investigation on Tidal Land Reclamation in Korea Using Satellite Image Data, Proc. of the 17th ACRS, G-4-1?6,.
