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Effects of tidal fluctuations on mixing and spreading in coastal aquifers: Homogeneous case
Author(s) -
Pool María,
Post Vincent E. A.,
Simmons Craig T.
Publication year - 2014
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1002/2014wr015534
Subject(s) - hydrogeology , mixing (physics) , geology , aquifer , saltwater intrusion , groundwater , dispersion (optics) , dimensionless quantity , seawater , hydrology (agriculture) , mechanics , geotechnical engineering , oceanography , physics , optics , quantum mechanics
While the hydraulics of tidally dominated groundwater systems have been studied extensively, tidally induced solute spreading in the fresh‐saltwater transition zone of coastal aquifers remains largely unexplored. Here we systematically quantify tidal impacts on solute mixing and spreading in seawater intrusion problems for an idealized homogeneous system. Mixing is characterized by the spatial moments of the solute concentration distribution and quantified by an effective dispersion coefficient. Parametric analysis reveals that the key dimensionless parameter controlling the tidal mixing behavior is the tidal mixing number ( n t m) which depends on the tidal amplitude, the period and the hydraulic diffusivity. We find that forn t m ≤ 600 , tides lead to a significant impact on the shape and location of the interface. The maximum effect on transverse and longitudinal dispersion occurs for large values of storativity, a hydrogeologic parameter that has been previously understated in terms of its significance. Large storativity implies a nonuniform hydraulic response to the tidal forcing, such that the resulting nonuniform time‐dependent velocity field enhances mixing. As a result, the interface spreads mainly at the bottom of the aquifer, where the saline end of the mixing zone migrates seaward, whereas the spatial extent of low salt concentrations migrates landward. These insights critically underpin quantitative guidance on the inclusion and exclusion of tidal effects in the analysis of seawater intrusion.