The major aquifers in Turkey are installed in the carbonate rocks which cover more than 30% of the territory. The well karstified subcutaneous zone of these carbonate rocks have high permeability and large karstic openings such as caves and solution channels. The surface morphological features function as point recharge features which allow rapid inflow into the aquifers. Flow in these rock masses is dominantly of conduit type. Particularly in allocthonous carbonate rock masses, whose karstification bases are usually marked by non-karstic units or those of relict/dissected karst, the residence time is much shorter, which makes these rock masses "unreliable" for water sustainable use. In these systems the inflow is quickly discharged. Normally, these rock masses are not considered and developed as aquifers, which is due to the lack of a permanent phreatic (saturated) zone. However, these rock masses can provide an important storage media during flood periods which are followed by long-term droughts, an expected consequence of the climate change projections. Storage of flood water in surface storage structures such as dams has several disadvantages, including high loss by evaporation during dry periods. Well karstified rock masses which normally do not contain significant phreatic zone can be developed to capture and store the floods flush waters for later use. Construction of cutoff walls to elevate the discharge level (mostly springs) is proved to be an effective method in this regard. The type and design of the cutoff wall depends of the karst type developed in the rock mass. Based on the practices in Turkey, it is suggested that as a potential source of water, karst hydrogeological studies should be focused on well karstified carbonate rock masses with shallow karstification base which are not considered reliable aquifers so far, all this without ignoring the impact of this works in the dependent ecological systems. Climate change will alter the sustainability conditions of most water resources. Due to the consequences of climate change, most water resources will be "un-sustained". The methodology suggested herein is a contribution to the sustainable use of an un-sustained resource.

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