Application of spectral analysis of daily water level and spring discharge hydrographs data for comparing physical characteristics of karstic aquifers

Bivariate time series techniques (in spectral domain) of daily rainfall and water level of piezometers or discharge of springs in karstic aquifers are employed to evaluate the lag times (delay) of aquifers response to rainfall events. The evaluation results show that the physical characteristics of karstic aquifers can be compared with each other by using the outcomes of these analyses. With attention to dual porosity idea of karstic aquifers, two lag times (t1, t2) can be computed, which, are related to flow of water through larger fractures (conduit flow) and matrix of the rock (diffuse flow), respectively. Results obtained from these functions, correspond to the findings of physical characteristics, compiled from field investigations. Comparable to dual porosity idea in regard to recharge through the larger fractures (in the first step) and finer porosity of the rock (in the second step), the idea of ‘Dual Recharge’ in karstic aquifers is presented. Application of these techniques is verified using daily rainfall and water level of Qara, Sabzpooshan and Kaftarak piezometers and daily discharge of Qasreqhomsheh karst spring in Maharlu basin in Iran (52°20′–52°40′E and 29°20′–29°40′N) having different degree of karstification in their surroundings.