Is the Combination of Linearized Theoretical Analysis and Sand Column Experiment Always Suitable for Estimating the Complex Effective Porosity?

Abstract

Wave uprush and backwash make sand beach intermittently covered and exposed by surface flows in the swash zone. In this particular area, groundwater table is close to sand surface which is always significantly affected by the capillary effect, resulting in complicated groundwater table dynamics (Horn, 2006). Groundwater table dynamics in the coastal aquifer are related to various coastal problems including saltwater intrusion, structure stability and biodiversity (Liu, 2013;Qi et al., 2020;Teo et al., 2003).Vertical infiltration/exfiltration of seepage flow in the swash zone is the most important water exchange mode between surface wave and groundwater, which is several orders of magnitude greater than the lateral seepage flow (Turner & Masselink, 1998). Considering the effect of capillary fringe almost occurs in the vertical direction, sand column experiments were designed to give further understandings of the capillary effect under external forcing (Allègre et al., 2014;Cartwright et al., 2006). A series of sand column experiments were first designed to examine the capillary effect in the unidirectional watering and dewatering process. Gillham (1984) considered the groundwater table change with a small amount of water addition (0.3 cm). He pointed out it makes disproportionate rise (30 cm) of groundwater table in a very short time, which is due to a decreased specific yield as groundwater table approaches sand surface. Turner (1993) reported that tens of centimeters drop in groundwater table was measured during the dewatering process in the sand column when meniscus appears at sand surface. Such phenomenon was defined as the Wieringermeer effect (Hooghoudt, 1947). After investigating the effect of capillary fringe on pore-water pressure and the groundwater table variation, Hang and Liu (2018) further attributed this rapid and disproportionate change to the truncated capillary fringe and they demonstrated that when the groundwater table is close to the sand surface, the formation and disappearance of meniscus adjacent to the sand surface can make

The Effects of Truncating the Capillary Fringe on Water‐Table Dynamics During Periodic Forcing

“…In addition, TF = 1.25 in this study (Figure 4f) is the condition under which no capillary truncation phenomenon occurs, corresponding to the sand‐column experiment carried by Nielsen and Perrochet (2000a, 2000b). The amplitude attenuation and phase lag can be attributed to the damping effect caused by sands, which results in certain energy loss (Yang et al., 2021).…”

“…Recently, Yang et al. (2021) presented an analytical solution for the sand column hydrodynamic under truncated conditions using a perturbation approach that suggests the importance of the high‐order harmonic components.…”

“…Hang and Liu (2018) analyzed and compared different capillary fringe behaviors under different TF conditions. Recently, Yang et al (2021) presented an analytical solution for the sand column hydrodynamic under truncated conditions using a perturbation approach that suggests the importance of the high-order harmonic components.…”