|Some processes in the sea-water/fresh-water interface, as influenced by the presence of gases|
Goldenberg, L.C.; Mandel, S. (1989). Some processes in the sea-water/fresh-water interface, as influenced by the presence of gases, in: De Breuck, W. et al. (Ed.) Proceedings of the 10th Salt-Water Intrusion Meeting Ghent (Belgium), 16-20 May 1988. Natuurwetenschappelijk Tijdschrift, 70(1-4): pp. 288-299
In: De Breuck, W.; Walschot, L. (Ed.) (1989). Proceedings of the 10th Salt-Water Intrusion Meeting Ghent (Belgium), 16-20 May 1988. Natuurwetenschappelijk Tijdschrift, 70(1-4). Natuurwetenschappelijk Tijdschrift: Gent, Belgium. 408 pp., more
In: Natuurwetenschappelijk Tijdschrift. L. Walschot/Natuur- en Geneeskundige Vennootschap: Gent. ISSN 0770-1748, more
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|Document type: Conference paper|
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- Goldenberg, L.C.
- Mandel, S.
Gases may influence processes in zones of fresh-water/sea-water interface of coastal aquifers. One of the sources of gas bubbles is recharge wells. The bubbles of gas, alone or in combination with clay particles, impair flow. The flow impairment may not allow the use of the recharged water for sea-water intrusion. Results of laboratory experiments that simulated circumstances of an operating recharge well indicate the following trends : 1)quasi-stable bubble-mineral particle units form due to adhesion of hydrophobic colloids (clay minerals) on the surface of air bubbles. The units may become mobile when the pressure gradient in the porous medium is larger than a threshold value. Sometimes, several units may arrive in a large void and accrue; 2)introduction of a small volume of air in pure sand induces a steady state of slightly reduced permeability, if either a concentrated solution ('sea-water') or a dilute solution ('fresh water') fills the pores. Some bubbles stabilize in the conducting pores, and reduce permeability. A slug flow may occur through the rest of the pores. A lower permeability is attained in a sediment where equilibrium exists between the electrical atmosphere of the clay platelets attached on the bubbles and the surrounding solution, and/ or if the electrical atmosphere is suppressed by a concentrated solution. The lower permeability is due to : a) stabilization of bubbles in a non-spherical shape by adhered platelets; elongated parts of the bubbles penetrate into the near pores, increase flow paths tortuosity and decrease the cross-sectional area available to flow; and, b) several bubbles may become connected by a 'cement' made of flocculated particles; the agglomerates of bubbles occupy several interconnected pores and impair flow. The lower permeability obtained in these ways is, however, a transient, partially reversible situation. The 'cement' may be 'dissolved' by a solution with a low ionic concentration, and then the free bubbles may flow; 3)an irreversible decrease of permeability may be induced by the combined effect of bubbles and voluminous three-dimensional structures of smectite. Such a situation may arise when fresh water replaces sea-water in the pores of mixtures of sand and traces of smectite. The clay structures may reduce the cross-sectional area of the pores so that flow of bubbles is no longer possible. The bubbles, stabilized in conducting pores, stop the flow through the entire sediment. A state where the sediment in the vicinity of a borehole is clogged by bubbles and clay paricles reduces the efficiency of a well for serving as a recharge well. Injection of air into the sea-water/fresh-water interface may be used as a method for reducing sea-water encroachment.