Theoretical study of the impact of tide-induced airflow on hydraulic head in air-confined coastal aquifers

Abstract

Tide-induced hydraulic head fluctuation results in significant airflow above the water table if the aquifer is air-confined, for example, if the aquifer is capped by low permeability materials. Hypothetical studies on the interaction between tidal fluctuation and airflow in coastal aquifers are carried out using an air-water two-phase numerical model. The results show that both the amplitude of the hydraulic head fluctuation and the distance of influence of the tidal fluctuation increase due to the impact of airflow. For a fixed distance from the coastline, the amplitude of the hydraulic head fluctuation increases with depth, and the hydraulic head fluctuation at small depths lags that at great depths. Tide-induced airflow may be so strong that considerable errors in estimating hydraulic parameters could be generated when models are applied without considering airflow. In an air-confined aquifer, if airflow is neglected, the hydraulic diffusivity could be considerably overestimated. © 2010 IAHS Press.