Karstic aquifers

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Guest Editor
Research Scientist: Bernard Collignon
Head of the Water Resources Department at Hydroconseil (Avignon – France).
Email: collignon@hydroconseil.com

Manuscript Topics
Soluble rocks (limestone, dolomite but also salt and gypsum) cover only a small part of the Earth's surface (less than 10% of the land surface and less than 2% of the Earth's surface). However, these rocks have a special importance to humanity, because they host a large part (25%) of the groundwater resources used to supply cities and factories.

The aquifers in soluble rocks have a special feature: they contain large channels, dug by rock dissolution. We call them karstic aquifers, by reference to the region of Kras (in Slovenia) where these phenomena of dissolution are very spectacular.

The structure of these aquifers is particularly complex, because they are heterogeneous. They contain both voids smaller than mm (like all other rocks) and large voids, which will give them exceptional conductive properties: in such aquifers, it is not uncommon to observe circulation velocities exceeding one km/day (compared to the velocities of a few km/year that are generally measured in porous aquifers). This formidable conductivity has an immediate consequence: these are the aquifers most vulnerable to bacteriological pollution and it is therefore paramount to fully understand the circulation mechanisms, in order to be able to model it.

Unfortunately, the mere heterogeneity of these aquifers makes this modelling very difficult. The tools usually used by hydrogeologists (like Modflow ®) are effective in porous media but they are desperately imprecise in karst. There is not yet a modeling tool that correctly reflects the complex structure of karst (the combination of voids with very different sizes), particularly because this structure cannot be deduced from a few boreholes or a few measurement points. Modelling these aquifers is therefore a formidable challenge that many research teams around the world have taken up.

Karst aquifers are thus one of the most complex research objects for Earth sciences and this issue aims to gather original contributions on the methods and techniques of investigation of karst aquifers, notably on the following themes:

• Structure and properties of karst aquifers (how to characterize their heterogeneity and extrapolate from a few observation points);
• Borehole engineering in karstified rocks (analysis of specific difficulties to carry out drilling and to predict borehole yield);
• Karstification mechanisms : complex processes, leading to the creation of large voids, which play a fundamental role in aquifer conductivity; surface karstification (direct dissolution of the rock by rainwater) is the best known, as it is directly measurable, but deep drilling has revealed the existence of deep karstification (notably hydrothermal) which constitutes a new field of investigation;
• Karst springs : exceptionally large yield have guided human settlement and, conversely, induce the high use of these aquifers for drinking water supply and industry; these springs constitute an interesting observatory of the aquifer but they are not representative of everything that is happening within the aquifer;
• The complex chemistry of carbonate aquifer waters, due to the sensitive calco-carbonic balance; water saturation varies during transit in the aquifer, with alternating precipitation zones and dissolution zones;
• The great vulnerability of such aquifers to bacterial pollution, which requires implementation of protection areas; vulnerability mapping tools;
• Sustainable management of water resources in karst aquifers, taking into account their vulnerability, but also their specific advantages (the existence of channels that facilitate both large-flow pumping and reinjection).

Contributions could be reviews or standard research papers.

Paper submission
 All manuscripts will be peer-reviewed before their acceptance for publication.
The deadline for manuscript submission is 15th December 2018

Instructions for authors
Please submit your manuscript to online submission system

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