Effects of Artificially Reducing Hydraulic Conductivity of Coastal Aquifers on Maximum Sustainable Withdrawal Rate

Traditional physical barriers for mitigating seawater intrusion are expensive and necessitate complex engineering measures such as excavation or piledriving. An alternative cost-effective method involves artificially reducing the hydraulic conductivity in the upper parts of selected areas (modified zones) using a precipitate. This study presents an analytical solution using the finite Fourier Cosine transform to evaluate the impact of a modified zone on mitigating seawater intrusion and improving the maximum sustainable withdrawal rate in a coastal confined aquifer. Numerical solutions employing the variable density flow code SEAWAT are conducted to validate the proposed analytical solution. Effects of hydraulic conductivity, length, and thickness of the modified zone, along with the well location on the interface toe location and maximum sustainable withdrawal rate are investigated. Additionally, the sensitivities of dimensionless parameters are accessed under various combinations of the length and thickness of the modified zone. Results show that the interface toe shifts inland with an increase in the dimensionless equivalent hydraulic conductivity (κ) and a decrease in the dimensionless length of the modified zone (l_D). Consequently, the maximum sustainable withdrawal rate increases as κ decreases and l_D increases. The location of the pumping well significantly influences the maximum sustainable withdrawal rate in aquifers with finite domains, considering both inland and lateral boundary conditions. Sensitivities of β = L/W and η = K₁H²/(q_f L) to the maximum sustainable withdrawal rate are an order of magnitude greater than the sensitivity of α_T,D = α_T/H, considering aquifer length (L), aquifer width (W), aquifer hydraulic conductivity (K₁), aquifer thickness (H), constant inland flux (q_f), and transverse dispersivity (α_T). These findings offer valuable insights for constructing modified zones to migrate seawater intrusion and for deploying pumping wells in coastal areas.