Comparison of Solutions of Coupled and Uncoupled Models for the Henry Problem

This paper uses the Henry problem to examine the conditions at which uncoupled models can be used to predict flowrates, flow directions, and saltwater intrusion in coastal aquifers when saltwater intrusion takes place. The SEAWAT model is used to determine results under both coupled and uncoupled conditions under various scenarios by changing: (a) the hydraulic conductivity anisotropy ratio K_r, defined as the ratio of the horizontal to the vertical hydraulic conductivity, K_h/K_v, from 1 in the original Henry problem to 1000, (b) the freshwater recharge rate Q_f from the original value of 5.702 m^3/day to 50% and 75% lower at different K_r conditions. The discrepancy between isochlor locations, groundwater flow directions, and the percent of recirculated seawater by the coupled and uncoupled models, decreased substantially with increasing K_r values. Even a K_r value of 20 produced very similar results. The discrepancy between the two sets of results, coupled versus uncoupled, increases when Q_f is reduced. However, the results from the two models match well for K_r = 100 even if Q_f is reduced by 75% of the original value used in Henry problem. It may be possible to use uncoupled models if the K_r = 100 or higher regardless of the freshwater recharge.