Hydraulic Head Fluctuations in an Intermediate Depth Coastal Surface Aquifer
Hydraulic Head Fluctuations in an Intermediate Depth Coastal Surface Aquifer
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DOI：
10.1016/j.jhydrol.2023.130017
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发表时间：
2023-08
影响因子：
6.4
通讯作者：
R. Housego;B. Raubenheimer;S. Elgar;Ming Zhi Wu
中科院分区：
文献类型：
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作者：
R. Housego;B. Raubenheimer;S. Elgar;Ming Zhi Wu
潮汐和风暴潮是沿海含水层地下水循环和通量的重要驱动因素。然而，很少有实地研究描述了沿海含水层对这两种强迫的响应。在这里，对一个大约 20 米深的障壁岛表层含水层进行了三年的水头观测，用于研究由日潮和半日潮以及风暴引起的涌浪和波浪驱动装置引起的海水水位变化驱动的波动的内陆传播。与之前的观测类似，观测到的水头波动幅度衰减率高于潮汐驱动水头波动的内陆相位滞后增加。此外，含水层深处的潮汐水头波动会导致靠近含水层表面的潮汐水头波动。相比之下，持续几天的风暴潮具有相似的振幅衰减率和内陆相位滞后增加率，并且水头波动大致是深度均匀的。非线性中间含水层深度理论（之前未与现场观测进行比较）描述了潮汐幅度和相位滞后的内陆和垂直变化，并崩溃为长周期波动的线性解，与风暴潮观测一致。通过将中间深度解拟合到观测到的潮汐振幅衰减和内陆相位滞后率来估计的扩散率与含水层特性一致，提供了一种利用沿海水头观测来表征含水层的方法。忽略毛细管效应、滞后和垂直分层（可能导致振幅衰减和相位滞后演化之间的差异）的数值模型模拟与观测结果相似，并支持含水层深度相对于水头波动波长的重要性。
Tides and storm surges are important drivers of groundwater circulation and fluxes in coastal aquifers. However, few field studies have characterized the response of the coastal aquifer to both forcings. Here, three years of hydraulic head observations in a roughly 20-m deep barrier island surface aquifer are used to investigate the inland propagation of fluctuations driven by ocean water-level changes owing to diurnal and semi-diurnal tides and storm-induced surge and wave-driven setup. Similar to prior observations, the observed rate of amplitude attenuation of the hydraulic head fluctuations is higher than the inland increase in phase lag for the tidally-driven head fluctuations. Additionally, tidal hydraulic head fluctuations deeper in the aquifer lead those nearer the surface of the aquifer. In contrast, storm surges with periods of several days have similar rates of amplitude attenuation and inland increase in phase lags, and hydraulic head fluctuations are roughly depth uniform. A nonlinear, intermediate aquifer-depth theory (not previously compared with field observations) describes the inland and vertical changes of tidal amplitudes and phase lags, and collapses to the linear solution for long period fluctuations, consistent with the storm surge observations. The diffusivity estimated by fitting intermediate depth solutions to the observed tidal amplitude attenuation and rate of inland phase lag is consistent with the aquifer properties, providing a method to characterize aquifers using coastal head observations. Numerical model simulations neglecting capillary effects, hysteresis, and vertical layering (which can cause discrepancies between amplitude attenuation and phase lag evolution) are similar to the observations and support the importance of the depth of the aquifer relative to the wavelength of the hydraulic head fluctuations.