The discharge-quality relationship interpreted for karst springs by a new karst model

Résumé

Puisque le drainage souterrain se fait dans des fractures de dimensions diverses, lorsque l'eau se fait rare, elle disparaît de ces fractures à des moments qui peuvent différer de quelques jours à plusieurs semaines. Ce mécanisme karstique explique aussi que les eaux qui s'infiltrent plus lentement deviennent plus douces, parce que leurs carbonates précipitent plus facilement dans la grotte. Les eaux plus dures sont celles qui coulent plus vite, et elles rendent la résurgence plus chargée en carbonates tant qu'elles bloquent les eaux plus douces dans les passages latéraux étroits.

Abstract

Experiments carried out in Hungary have implied that the karst mechanism which controls the variation in spring discharge during depletion also applies to changes in some quality components in the spring water. The earlier studies by CSER and MAUCHA in Hungary have demonstrated the depletion discharge turne series to describe in a logarithmic plot a five-sided polygon. The phenomenon is attributable to the successive depletion of five duct systems having different cross sectional areas at significantly different rates. The flow in the wider ducts causes backup in the narrower laterals and thus prevents the latter from becoming depleted, with the consequence that for a few days at times of flood, radical changes may take place in the composition of the spring discharge. Taking also into consideration the circumstance that from the waters seeping at slower rates more carbonates are likely to precipitate in die cave (the water becoming softer in the process), the more highly concentrated (harder) directly infiltrating high flows in the cave may produce higher concentrations in the spring discharge by blocking temporarily the softer waters in the lacerai. passages. It is true if the waters don't originate from sinkholes. In limestone areas, if the seepage waters depleting at a slower rate originate from limestone, an increase in the Ca- and ¹¹CO₃ -ion contents is alone observable. However, if these waters originate from both limestone and dolomitic rocks, then the concentration of the Mg-ions will also decrease in the composition of die high spring discharges. Observation data have fully corroborated die described mechanism.

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Over : G. IZAPY

Over : L. MAUCHA