The Impact of the Degree of Aquifer Confinement and Anisotropy on Tidal Pulse Propagation
The Impact of the Degree of Aquifer Confinement and Anisotropy on Tidal Pulse Propagation
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DOI：
10.1111/gwat.12509
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发表时间：
2017-07
期刊：
影响因子：
2.6
通讯作者：
P. Shuai;P. Knappett;S. Hossain;A. Hosain;Kimberly A. Rhodes;Kazi Matin Uddin Ahmed;M. Cardenas
中科院分区：
文献类型：
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作者：
P. Shuai;P. Knappett;S. Hossain;A. Hosain;Kimberly A. Rhodes;Kazi Matin Uddin Ahmed;M. Cardenas
海洋潮汐波动沿海岸河流长距离传播，可以用来限制河岸含水层的水力特性。然而，这些估计数可能对含水层限制程度和含水层各向异性很敏感。本文分析了孟加拉国Meghna河沿着受潮汐影响的含水层的水力学特性，采用了：（1）段塞试验结合钻井测井和表面电阻率来估算渗透率（T），（2）抽水试验来估算T和储水率（S），从而估算含水层扩散率（DPT）;以及（3）观察到的潮汐脉冲的幅度和速度的减小，以使用Jacob‐Ferris分析解来计算D。用段塞试验和钻孔岩性估计的平均导水率（K）和T分别为27.3 m/d和564 m2/d。抽水试验确定的T和S值分别为400 ~ 500 m2/d和1 ~ 5 × 10−4，DPT为9 ~ 40 × 105 m2/d。相比之下，Jacob‐Ferris模型估计的D范围为0.5至9 × 104 m2/d。我们假设这一误差是由于真实的含水层条件与Jacob‐Ferris模型假设的含水层条件存在偏差。使用2D数值模型，在一系列条件下模拟潮汐脉冲，并使用Jacob‐Ferris模型计算D。中等承压（Ktop/K含水层10）产生的D在实际值的2倍以内。抽水试验和Jacob‐Ferris模型之间D的数量级差异表明限制或各向异性很小。
Oceanic tidal fluctuations which propagate long distances up coastal rivers can be exploited to constrain hydraulic properties of riverbank aquifers. These estimates, however, may be sensitive to degree of aquifer confinement and aquifer anisotropy. We analyzed the hydraulic properties of a tidally influenced aquifer along the Meghna River in Bangladesh using: (1) slug tests combined with drilling logs and surface resistivity to estimate Transmissivity (T); (2) a pumping test to estimate T and Storativity (S) and thus Aquifer Diffusivity (DPT); and (3) the observed reduction in the amplitude and velocity of a tidal pulse to calculate D using the Jacob‐Ferris analytical solution. Average Hydraulic Conductivity (K) and T estimated with slug tests and borehole lithology were 27.3 m/d and 564 m2/d, respectively. Values of T and S determined from the pumping test ranged from 400 to 500 m2/d and 1 to 5 × 10−4, respectively with DPT ranging from 9 to 40 × 105 m2/d. In contrast, D estimated from the Jacob‐Ferris model ranged from 0.5 to 9 × 104 m2/d. We hypothesized this error resulted from deviations of the real aquifer conditions from those assumed by the Jacob‐Ferris model. Using a 2D numerical model tidal pulses were simulated across a range of conditions and D was calculated with the Jacob‐Ferris model. Moderately confined (Ktop/Kaquifer 10) yield D within a factor of 2 of the actual value. The order of magnitude difference in D between pumping test and Jacob‐Ferris model at our site argues for little confinement or anisotropy.