Grid-enabled Monte Carlo analysis of the impacts of uncertain discharge rates on seawater intrusion in the Korba aquifer (Tunisia)

Figures & data

Fig. 1 Location map of the Korba aquifer and geological settings (squares are 10 × 10 km). Hydraulic heads observed in August 2004 are also shown.

Fig. 2 (a) Average pumping rates map after Kerrou et al. (2010) with the location of the exhaustive pumping rate survey (dashed line polygon). (b) Scatter plot of estimated Q_c versus measured Q_m pumping rates; (c) histogram of the residual e; and (d) experimental (o) and model (––––) variograms of the error.

Fig. 3 The Korba aquifer 3-D numerical model, modified after Kerrou et al. (2010). Note that wells were attributed at around 10 m from model surface and the lateral fluxes were integrated over the Pliocene formation thickness. Element sizes range from 150 to 200 m in the main aquifer and between 50 and 100 m near the shoreline. Vertically, the mesh is divided into 19 layers with 5 m thickness on average.

Fig. 4 Scatter plot showing the fits between the observed and calculated concentrations: (a) heads (m) and (b) salt concentrations (g/L). In both cases, observed values ±RMSE (root mean squared error) are also shown.

Fig. 5 (a) and (b) Example maps of the pumping rates (Q_c 1996). (c) and (d) Histograms of pumping rates for wells 240 and 361. (e) Time-dependent evolution functions for both wells (Q ₂₄₀: ––– and Q ₃₆₁: - - - -) with 1996 volumes as reference.

Fig. 6 Ensemble average maps for the 100 realizations: (a) head H (m); and (b) relative concentration C (‐).

Fig. 7 Histograms of: (a) and (b) head H (m), and (c) and (d) relative concentration C (‐) in wells Q ₃₆₁ and Q ₂₄₀, respectively. Ensemble average (––––) and ensemble average ±2 ensemble standard deviations (grey lines) are also shown.

Fig. 8 Probability map for a point (a) to be under the mean sea level and (b) to exceed the 0.1 relative salt concentrations. Both maps show 0.95, 0.75, 0.5, 0.25 and 0.05 isoprobability contours.

Fig. 9 Time evolution of the uncertainty: Q (grey polygon) represents the total estimated exploitation volume (hm³), U_H is the ratio (%) between the uncertain area with respect to the probability of falling below sea level and the onshore aquifer area; and U_C is the ratio (%) between the uncertain area with respect to the probability of exceeding 0.1 relative concentration and the onshore aquifer area.

Kerrou , J. , Renard , P. and Tarhouni , J. 2010 . Status of the Korba groundwater resources (Tunisia): observations and three-dimensional modelling of seawater intrusion . Hydrogeol. J. , 18 ( 5 ) : 1173 – 1190 . doi:10.1007/s10040-010-0573-5

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