engleski

The impact of scale effect in the defining of hydraulic conductivity of covering aquitard on the groundwater recharge and groundwater pollution

The paper presents the estimation of groundwater recharge through semipermeable covering deposits by various methods which has directly impact on the groundwater pollution. The pore (alluvial) aquifers are mainly covered by semipermeable silty-sandy deposits (covering aquitard) which have different thickness. The transition from slight to greater thickness integrates regional and heavy local features resulting in very irregular changes in the thickness of the cover. Within aquitards, the change of different types of soil usually occurs affecting their lithologic variety, i.e. their individual permeability, thus consequently the leakage through the aquitard. But, due to the deformations in spacial continuity, the layers having lowest permeability do not cause a regional impermeability of the entire aquitard. Owing to heavy difficulties that happen during direct measurements of groundwater recharge, a common opinion is that the estimated groundwater recharge under natural conditions is greater due to heavy drawdowns caused by an intense groundwater pumping. However, the groundwater recharge under natural conditions is dominantly affected by a regional groundwater flow, while, during the intense groundwater pumping, the effect of local hydrogeological conditions is much stronger. The difference between regional and local conditions can be explained by the so-called "scale effect" within which three observation levels are recognised: the laboratory, local and regional scales.

hydraulic conductivity; groundwater recharge; scale effect

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