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Governing equations for acid water in canals

It is giVen in this study governing equation system formulation for acid water movement in canals, especially, in the Plain of Reeds .of Vietnam where the jurbanite equilibrium is found dominant. It is assumed in the model a chemical equilibrium, however a kinetic treatment is also used to deal with redissolution of precipitates and sedimentation. | T~p chi Cc Journal of Mechanics, NCNST of Vietnam T. XVI, 1994, No 4 {21 - 27) GOVERNING EQUATIONS FOR ACID WATER IN CANALS NGUYEN TAT DAC Institute of Applied Mechanics Ho Chi Minh City SUMMARY. It is giVen in this study governing equation system formulation for acid water movement in canals, especially, in the Plain of Reeds .of Vietnam wh-ere the jurbanite equilibr ium is found dominant. It is assumed in the model a chemical equilibrium, however a kinetic treatment is also used to deal with redissolution of precipitates and sedimentation. 1. INTRODUTION An estimated 1.8 million hectares or approximately 45 percent of the-Mekong Delta in Vietnam is covered by acid sulphate soils. It is a problem to put thes·e soils to productive use. In the parts of Mekong Delta acidity in the surface water is a particular problem at the beginning of the rainy season. During the dry season acidity is formed in the soils and moves up to field surface, the .first rains of the rainy season wash the formed acidity in high concentrations to the canal system: . The physical, chemical and biological processes which control the movement of substances in canals and in soils are many and quite complicated. For canal water, some of the physical processes invOlved are longitudinal, lateral- and vertical dispersion, advection, sedimentation. Chemical processes comprise ionic exchange, hydrolysli3, oxidation-reduction, precipitation and adsorption. These processes are all directly or indirectly affected by hydro-m.eteorological parameters such as rainfall, run-off, temperature, evaporation and wind etc. Quantitative models for each of the processes above are very complex. Therefore there exists a number of approaches using deterministic and stochastic simulation but the selection will of course depends _on the specific application envisaged. In spite of the difficulties involved much Work has been caiTied out on the construction of deterministic canal water quality models because of their