The effect of cutoff walls on saltwater intrusion and groundwater extraction in coastal aquifers

Abstract

Summary We use numerical simulations to study the effect of cutoff walls on saltwater intrusion and assess their protective effect on groundwater extractions near the coast. Results are presented in terms of dimensionless variables with ranges suitable for field applications. We find that, in the absence of groundwater extractions, the effectiveness of cutoff walls is determined by the wall depth, its distance from the coast, the velocity ratio, the intensity of mixing, the conductivity anisotropy and the relative conductivity of the wall. To assess the effectiveness of cutoff walls in practical applications, we present graphs and empirical equations. Also, we assess the protective effect of cutoff walls on groundwater extractions by means of drains and single wells. We do so by calculating the maximum safe extraction rate before and after the construction of a cutoff wall; i.e. the maximum rate of groundwater extraction for which the maximum salt concentration entering the drain or the well is below a certain threshold. We find that the protective effect of cutoff walls is stronger for single wells rather than drains and for cases when the extractions are located at relative small distances from the coast, relative large depths, and in aquifers with small velocity ratio, weak mixing and high anisotropy. To facilitate the design of safe extractions, we use numerical results to develop analytical approximations for the influence of cutoff walls.