Journal of Cave and Karst Studies - ISSN 1090-6924
Volume 63 Number 1: 33-40 - April 2001

A publication of the National Speleological Society

Response of karst aquifers to rainfall and evaporation, Maharlu Basin, Iran
Nozar Samani

Abstract

Maharlu basin, with an approximate surface area of 4000 km2, is located in the central part of Fars Province, Iran. The basin is the first candidate site for karst hydrogeology research in the country. The karstified Asmari-Jahrum Formation covers ~37% of the total surface area of the basin with huge reservoirs of karst water. To establish the relationship between rainfall and evaporation with groundwater level and spring discharge, the fluctuations of groundwater level at nine piezometric and exploration wells, discharge of two springs, rainfall records, and pan evaporation are analyzed by employing time-series techniques both in time and frequency domains. Results are presented as correlograms, variance spectra, phase diagrams, coherency diagrams and cross correlograms. A time lag of 1-3 months was found between rainfall occurrence and the response of groundwater levels and spring discharges. There is no clear relation between evaporation and groundwater level and spring discharge. Different response in different wells is due to the different path lengths of percolated water from sinking point to the water table. The time response of groundwater level and spring discharge suggests that springs are fed through a diffuse karstic flow system that is in accordance with the physical characteristics of the springs. The lag times of Pirbanow and Pol-Brengi springs are equal in response to rainfall, but zero and 1-2 months respectively, in response to groundwater level at exploration well E-17. This point, together with the high value of specific conductivity of Pol-Brengi spring, suggests that the two springs have no hydrogeologic connection. The Ghasrodasht Fault may be the cause of this separation. It is finally concluded that a combination of time series analysis/physical properties of springs and geologic evidence can provide useful information about the hydrogeology of a region prior to large-scale and expensive tests.

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