Analysis of an Unconfined Aquifer Subject to Asynchronous Dual-Tide Propagation
Article first published online: 9 JAN 2008
No claim to original US government works
Volume 46, Issue 2, pages 239–250, March–April 2008
How to Cite
Rotzoll, K., El-Kadi, A. I. and Gingerich, S. B. (2008), Analysis of an Unconfined Aquifer Subject to Asynchronous Dual-Tide Propagation. Groundwater, 46: 239–250. doi: 10.1111/j.1745-6584.2007.00412.x
- Issue published online: 9 JAN 2008
- Article first published online: 9 JAN 2008
- Received June 2007, accepted October 2007.
Most published solutions for aquifer responses to ocean tides focus on the one-sided attenuation of the signal as it propagates inland. However, island aquifers experience periodic forcing from the entire coast, which can lead to integrated effects of different tidal signals, especially on narrow high-permeability islands. In general, studies disregard a potential time lag as the tidal wave sweeps around the island. We present a one-dimensional analytical solution to the ground water flow equation subject to asynchronous and asymmetric oscillating head conditions on opposite boundaries and test it on data from an unconfined volcanic aquifer in Maui. The solution considers sediment-damping effects at the coastline. The response of Maui Aquifers indicate that water table elevations near the center of the aquifer are influenced by a combination of tides from opposite coasts. A better match between the observed ground water head and the theoretical response can be obtained with the proposed dual-tide solution than with single-sided solutions. Hydraulic diffusivity was estimated to be 2.3 × 107 m2/d. This translates into a hydraulic conductivity of 500 m/d, assuming a specific yield of 0.04 and an aquifer thickness of 1.8 km. A numerical experiment confirmed the hydraulic diffusivity value and showed that the y-intercepts of the modal attenuation and phase differences estimated by regression can approximate damping factors caused by low-permeability units at the boundary.