The effects of oscillation period on groundwater wave dispersion in a sandy unconfined aquifer: Sand flume experiments and modelling

Abstract

This paper presents a new laboratory sand flume dataset on the propagation of groundwater waves in an unconfined sandy aquifer with a vertical boundary subject to simple harmonic forcing with a wide range of oscillation period from 10.7s to 909s. The data is unique in that it covers a much wider range of non-dimensional aquifer depths, nωd/K (where n is the porosity, ω is the angular frequency, d is the aquifer depth and K is the hydraulic conductivity) than has been previously investigated. Both the amplitude decay rate and rate of increase in phase lag of the water table waves are observed to monotonically increase with increasing oscillation frequency (increasing nωd/K). This is in contrast to existing theoretical dispersion relations which predict: (1) zero phase lag or standing wave behaviour and (2) an asymptotic decay rate as the frequency increases. Possible influences on the experimental data including sand packing, measurement location, finite amplitude wave effects, unsaturated zone truncation and multiple wave mode effects are unable to explain the discrepancy. The data was also compared against numerical solutions of Richards' equation with and without hysteresis and in both cases, the same qualitative behaviour as the analytic solutions described above is found. The discrepancy between data and predictions remains unexplained and highlights a knowledge gap that requires further 3 investigation. These findings relate directly to practical applications in the field of surface-groundwater interactions such as the influence of wave forcing of coastal aquifers on contaminant transport, sediment mobility and salt-water intrusion all of which are influenced by the dispersion of the groundwater wave.

The Dynamics of Sea Tide-Induced Fluctuations of Groundwater Level and Freshwater-Saltwater Interface in Coastal Aquifers: Laboratory Experiments and Numerical Modeling

“…The tidal wave used in the experiments is harmonic with constant amplitude. During all the experiments, the water levels at the boundaries were kept lower than 35 cm (Figure 1), in order to enable an unsaturated zone above the water table and to avoid problems that truncation of this area may create [29]. The freshwater in the experiment is colorless tap water, and the saline water is prepared by dissolving NaCl in tap water and adding commercial red food dye (AmeriColor Ltd.).…”

Field evidence of swash groundwater circulation in the microtidal rousty beach, France

“…Subterranean flows within sedimentary beaches or coastal barriers are indirectly carried out at large scale from measurements of watertable fluctuations [18,19]. Finer descriptions of beach groundwater dynamics are alternatively provided by numerical simulations [20] or laboratory experiments [21,22,23,24,25,26]. Above the intersection between watertable and beach surface, the dynamics of sand saturation in response to waves and tides is quite complex [27].…”

Modelling the effects of porous media deformation on the propagation of water-table waves in a sandy unconfined aquifer

“…which was in contrast to existing theories which predict (1) zero phase lag or standing wave behaviour and (2) an asymptotic decay rate as the frequency increases. Shoushtari et al (2016) considered possible influences like sand packing, measurement location, finite amplitude wave effects, unsaturated zone truncation and multiple wave mode effects but none of them can explain the observed discrepancy. They also compared laboratory data against numerical solutions of hysteresis and non-hysteresis Richards' equation (Richards, 1931) and in both cases, the same qualitative behaviour as the analytic solutions described above was found.…”

“…2013) and capillary effects (Barry et al, 1996;Li et al 2000). A summary of the existing analytical dispersion relationships can be found in Shoushtari et al (2016). Shoushtari et al (2016) presented an extensive laboratory sand flume dataset on the propagation of groundwater waves in an unconfined sandy aquifer with a vertical boundary subject to simple harmonic forcing with a wide range of oscillation period from 10.7s to 909s.…”

“…A summary of the existing analytical dispersion relationships can be found in Shoushtari et al (2016). Shoushtari et al (2016) presented an extensive laboratory sand flume dataset on the propagation of groundwater waves in an unconfined sandy aquifer with a vertical boundary subject to simple harmonic forcing with a wide range of oscillation period from 10.7s to 909s. Their data showed a monotonic increase in both amplitude decay rate and rate of increase in phase lag of the water table waves with increasing oscillation frequency…”