The shallow poroelastic aquifer: river response to solid Earth tidal forcing
Abstract
The water flux through rivers is chiefly determined by the intermittent charging of groundwater in laterally extensive shallow aquifers aquifers by rainfall and drawdown by seepage to the river bank. Here we show that the pattern of drawdown is modulated by the small-scale forcing of shallow poroelastic aquifers by the solid Earth tides. We use a shallow poroelastic model of flow in a deformable matrix to show that the modulation of the solid stress by solid Earth tides gives rise to the observed 2-4 cm height variation in the far-field aquifer depth. This impact of solid Earth tides on pore-pressure variations in deep, or confined aquifers, has been demonstrated previously [1,2] and may be used to characterise the hydraulic properties of the near well-bore environment [3]. To date, the solid Earth tidal signal has not unambiguously been recorded in shallow or surface aquifers. More importantly, the oscillatory motion of the groundwater table driven by the solid Earth tide also drives a modulation of the water flux into the river which is apparent in long-term records of the stream flux. By understanding the poroelastic response of aquifers to solid Earth tides as observed in river flux data, we are therefore able to infer properties of distributed aquifers from readily available records of the river flux. Here we demonstrate the link between solid Earth tides in the Quiock creek catchment, Guadeloupe, through the detailed record of the groundwater table in a transect of shallow bore holes extending 30 metres from the stream, along with time-resolved measurements of the river discharge.
[1] Bredehoeft, J. D. (1967). Response of well-aquifer systems to Earth tides. J. Geophys. Res., 72(12), 3075-3087. [2] Allègre, V., Brodsky, E. E., Xue, L., Nale, S. M., Parker, B. L., & Cherry, J. A. (2016). Using Earth-tide-induced water pressure changes to measure in situ permeability: A comparison with long-term pumping tests. Water Res. Res., http://doi.org/10.1002/2015WR017346 [3] Xue, L., Li, H.-B., Brodsky, E. E., Xu, Z.-Q., Kano, Y., Wang, H., et al. (2013). Continuous permeability measurements record healing inside the Wenchuan earthquake fault zone. Science, 340(6140), 1555-1559.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H53R2068N
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGY;
- 1832 Groundwater transport;
- HYDROLOGY;
- 1835 Hydrogeophysics;
- HYDROLOGY;
- 1847 Modeling;
- HYDROLOGY