76 A new concept of karst development based on hydrogeology and geophysics The dual-porosity model incorporating the flow dimension approach enables the calibration of all observed drawdown curves with a standard error less than 0.02. The matrix/discontinuity skin factor explains the various shapes observed in both the drawdown curves and their corresponding derivatives. An illustrative example is presented in Figure 15. The calibration was performed on both the drawdown curve and its derivative from a pumping test conducted at the HES. Graphs (a) show the drawdowns measured at observation well M19 during pumping at M21 (Q = 62.3 m3/h). The test was calibrated using a skin factor value of Sf = 0. When the skin factor increases (Sf = 0.5 to 5), a plateau begins to appear on the drawdown Figure 15 Drawdown and derivative curves with and without Skin.
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