Volume 3, Issue 1 (11-2009)
Abstract
(Paper pages 543-562) When two solutions are mixed, concentrations in the mixture are volume-weighted averages of the two end-members, but the thermodynamic activities of the species controlling the water–mineral reactions are non-linear functions of the mixing ratio. Therefore, two end member solutions in equilibrium with carbonate phase could lead to a mixture undersaturated with respect to carbonate. A favorite place for this phenomenon is water table, where mixing of different waters is taking place. In this paper, Porosity change in freshwater lens of an island was calculated by coupling dissolution potential with a variable density flow and solute transport model. The effect of permeability enhancement on the rate of porosity change was evaluated. Dissolution due to this mixing takes place in water table and active edge of freshwater lens (40m from coastline). The results indicate an increase rate of 0.6×10-3 percent of porosity per year. Permeability enhancement increases the rate of dissolution and porosity change in fresh water lens.
M Haedari, Mh Ghobadi, M Torabi Kaveh,
Volume 5, Issue 2 (4-2012)
Abstract
In the karstic areas, detailed studies of phenomena such as seepage of water from hydraulic structures and land subsidence in the residential and quarry areas is of higher importance. In this study, the dissolution rate constant of gypsite samples of Gachsaran Formation, obtained from the Chamshir dam reservoir, were measured equal to 0.24×10-3 cm/sec. Then, the changes of amounts of joint apertures using theoretical and experimental (by changes of joint water flowing and direct measurement) methods were calculated. The results showed that the predicted aperture for joints calculated through theoretical method is less consistent with the measured value of the changes of joint water flowing while the value measured by direct method (measured using a caliper) compliance is higher. Also based on research findings, if gypsites of the dam reservoir are exposed to the water flow, the amount of aperture of a joint with 0.5 cm initial opening will increase to 10 cm after about 278 days. This increase in joint aperture compared with the useful life of the dam draws for special attention to water tightening of dam reservoir.
