Simulation of brackish karst springs operation with the MODKARST deterministic model

A simulation is presented of the operation of brackish karst springs with the MODKARST
deterministic mathematical model. Through this simulation, major issues regarding the
operation mechanisms as well as the sustainable development of the springs are
addressed and analyzed. The particular case analyzed is the Almiros brackish karst
spring at Heraklion Crete in Greece and the Makaria brackish karst spring in Attica. Of
concern are the following aspects: (a) The fractal characteristics of the Almiros karst
formation, (b) the sea intrusion mechanism for the Almiros spring and the Makaria spring
and (c) the choice of a suitable method for the sustainable development of the Almiros
spring. It was found that the seawater intrusion in the Almiros karst-spring reservoir
follows a power law, the exponent of which provides the fractal dimension of the system.
Regarding sea intrusion, the spring becomes brackish due to the crossing of the tube,
which carries the fresh water to the spring, with other tubes, carrying saltwater from the
sea. MODKARST simulates the hydrograph along with the variation with time of the
chloride concentration and correlates the discharges from the fresh water and the
seawater tubes. The outcome is the relative importance of the two potential mechanisms
for seawater intrusion, namely the density difference between fresh water and sea water
and the venturi effect; it is found that the density difference dominates in the Almiros case
while the Venturi effect dominates in the Makaria case. An important conclusion of the
analysis is that raising the Almiros-spring water outlet could prevent the seawater
intrusion; the location of the elevated outlet and the fresh water loss to the sea are
estimated.