Jiu Jimmy Jiao

An analytical solution of groundwater response to tidal fluctuation in a leaky confined aquifer

An analytical solution is derived to investigate the influence of leakage on tidal response in a coastal leaky confined aquifer system. The analytical solution developed here is more general than the traditional solution obtained by Ferris [1951], which can be regarded as a special case of the solution presented in this paper. This solution is based on a conceptual model under the assumption that the groundwater level in the confined aquifer fluctuates in response to sea tide while that of the overlying unconfined aquifer remains constant. This conceptual model is supported by numerous field studies by previous researchers which have demonstrated that the tidal response in an unconfined aquifer may be negligible compared to that in a confined aquifer. The leakage has a significant impact on the tidal behavior of the confined aquifer. Hypothetical studies indicate that both tidal amplitude of groundwater head in the aquifer and the distance over which the aquifer can be disturbed by the sea tide will be considerably reduced because of the existence of leakage. This analytical solution is used to investigate the tidal and piezometer data at the Chek Lap Kok airport, Hong Kong Special Administrative Region, Peoples Republic of China.

Tide-induced groundwater fluctuation in a coastal leaky confined aquifer system extending under the sea

This paper presents the analytical solution of groundwater response to tidal fluctuation in a coastal multilayer aquifer system consisting of a leaky confined aquifer, a semipermeable layer, and an unconfined aquifer. The semipermeable layer, or the roof of the leaky confined aquifer, extends under the sea. Comparisons are made with solutions derived previously, which considered only a single aquifer, zero extension of the roof, or infinite roof length, and demonstrate that the previous solutions are special cases of the solution presented here. A hypothetical example is used to discuss the impact of the dimensionless roof length, dimensionless leakage, and tidal efficiency on the groundwater level fluctuations in the inland part of the confined aquifer. The fluctuation decreases significantly with the roof length when the roof length is small but is insensitive to the change of roof length when the roof length is greater than a threshold. The impacts of leakage from the offshore and inland portions of the confining unit are different. Leakage from the offshore portion tends to increase the fluctuation of the groundwater level, while leakage from the inland portion tends to decrease the fluctuation. The fluctuation increases as the tidal efficiency increases. This fact is significant only when the roof length is great and leakage is small.

Tide-induced seawater–groundwater circulation in a multi-layered coastal leaky aquifer system

Abstract Mean groundwater levels of a multi-layered coastal leaky aquifer system are considered. The system consists of an unconfined aquifer, a confined aquifer and a semi-permeable layer between them. Both exact asymptotic solutions and approximate perturbation solutions are derived for multi-sinusoidal-component sea tide. At inland places far from the coastline, the perturbation solutions show a good agreement with the exact asymptotic solutions. Due to the watertable-dependent transmissivity of the unconfined aquifer, the mean groundwater levels of the aquifer system stand considerably above the mean sea level even in the absence of net inland recharge of groundwater and rainfall. These lead to landward positive gradients of both the mean watertable and mean head in the region near the coastline, which consequently results in a seawater–groundwater cycle. Seawater is pumped into the unconfined aquifer by the sea tide and divided into two parts. One part returns to the sea driven by the mean watertable gradient. The rest part leaks into the confined aquifer through the semipermeable layer, and returns to the sea through the confined aquifer driven by the mean head gradient. The total discharge through the confined aquifer is significant for coastal leaky aquifer system with typical parameter values. This seawater–groundwater cycle has impacts on better understanding of submarine groundwater discharge and exchange of various chemicals such as nutrients and contaminants in coastal areas. If the observed mean water levels in coastal areas are used for estimating the net inland recharge, the enhancing processes of sea tide on the mean groundwater levels should be taken into account. Otherwise, the net inland recharge will be overestimated.

Analytical studies of groundwater-head fluctuation in a coastal confined aquifer overlain by a semi-permeable layer with storage

Abstract Analytical studies are carried out to investigate groundwater-head changes in a coastal aquifer system in response to tidal fluctuations. The system consists of an unconfined aquifer, a semi-confined aquifer and a semi-permeable confining unit between them. An exact analytical solution is derived to investigate the influences of both leakage and storage of the semi-permeable layer on the tide-induced groundwater-head fluctuation in the semi-confined aquifer. This solution is a generalization of the solution obtained by Jiao and Tang (Water Resource Research 35 (1999) 747–751) which ignored the storage of the semi-confining unit. The analytical solution indicates that both storage and leakage of the semi-permeable layer play an important role in the groundwater-head fluctuation in the confined aquifer. While leakage is generally more important than storage, the impact of storage on groundwater-head fluctuations changes with leakage. With the increase of leakage the fluctuation of groundwater-head in the confined aquifer will be controlled mainly by leakage. The study also demonstrates that the influence of storativity of the semi-permeable layer on groundwater-head fluctuation is negligible only when the storativity of the semi-permeable layer is comparable to or smaller than that of the confined aquifer. However, for aquifer systems with semi-permeable layer composed of thick, soft sedimentary materials, the storativity of the semi-permeable layer is usually much greater than that of the aquifer and its influence should be considered.

Analytical solutions of tidal groundwater flow in coastal two-aquifer system

Abstract This paper presents a complete analytical solution to describe tidal groundwater level fluctuations in a coastal subsurface system. The system consists of two aquifers and a leaky layer between them. Previous solutions of Jacob [Flow of groundwater, in: H. Rouse (Ed.), Engineering Hydraulics, Wiley, New York, 1950, pp. 321–386], Jiao and Tang [Water Resour. Res. 35 (3) (1999) 747], Li and Jiao [Adv. Water Resour. 24 (5) (2001a) 565], Li et al. [Water Resour. Res. 37 (2001) 1095] and Jeng et al. [Adv. Water Resour. (in press)] are special cases of the new solution. The present solution differs from previous work in that both the effects of the leaky layers elastic storage and the tidal wave interference between the two aquifers are considered. If the upper and lower aquifers have the same storativities and transimissivities, the system can be simplified into an equivalent double-layered, aquifer–aquitard system bounded by impermeable layers from up and down. It is found that the leaky layers elastic storage behaves as a buffer to the tidal wave interference between the two aquifers. The buffer capacity increases with the leaky layers thickness, specific storage, and decreases with the leaky layers vertical permeability. Great buffer capacity can result in negligible tidal wave interference between the upper and lower aquifers so that the Li and Jiao (loc. cit.) solution applies.

Tide‐induced groundwater level fluctuation in coastal aquifers bounded by L‐shaped coastlines

[1] This paper presents an analytical solution to describe tidal groundwater level fluctuations in an aquifer bounded by two water-land boundaries that form a right angle. The aquifer configuration can represent the situation of a right-angle corner in an island when the tidal boundaries are the same along both boundaries, or the estuary situation if the amplitude damps with distance along one boundary (river) and the amplitude along the other boundary (sea) does not change spatially. The two-dimensional flow equation subject to periodic boundary conditions is changed into a time-independent elliptic problem using complex transform. The elliptic problem is then solved using the Green’s function method. Li et al. [2000] obtained a nonperiodic solution to the same problem with an additional hypothetical initial condition. Their solution includes a time-dependent integral. The solution presented here is a significant improvement over theirs in the sense that the solution is periodic and computationally efficient since the integral involved is independent of time. An approximate solution without integral is also derived. An error analysis and a case study in Hong Kong demonstrate that the approximate solution is adequate for most field problems. INDEX TERMS: 1829 Hydrology: Groundwater hydrology; 1832 Hydrology: Groundwater transport; 1899 Hydrology: General or miscellaneous; 3384 Meteorology and Atmospheric Dynamics: Waves and tides; KEYWORDS: periodic groundwater flow, analytical solution, coastal aquifer, sea tide, L-shaped coastline

In situ rainfall infiltration studies at a hillside in Hubei Province, China

Field infiltration tests were conducted at a hillside near the ship lock of the Three Gorges Dam in Hubei Province, China. The test site consists of residual soil and decomposed granite. The infiltration rate is estimated from the in situ tests to be 1.465‐2.778◊10’6 ms ’1, depending on the initial water content. The rate at which the infiltration front moves down through the soil matrix within 2 m of the ground surface is estimated to be ca. 0.26 m day’1 on average. At the end of the in situ tests, the matric suction profiles show that the soil below a depth of 80 cm remained unsaturated, while the zone above was almost fully saturated. This finding was unexpected. The site was excavated after the test to examine the abnormal behaviour of the matric suction profiles in the depth. A relic joint was identified at a depth of 78 cm at an attitude almost parallel to the slope surface. It is surmised that the joint transmitted water laterally and limited further penetration of the wetting front. The water in the zone above the joint appeared to be ‘perched’. This experiment indicates that, to describe thoroughly the infiltration process within a weathered jointed granite profile for slope engineering design purposes, a model based on the assumption of a uniform porous media is inadequate. The model should include the discontinuities. This is challenging since it requires field studies to identify the pattern and distribution of the joints. The implications of the experimental results on slope stability are discussed. The in situ tests provide important information for further studying groundwater seepage under rainfall conditions and a dewatering system design for the slope above the ship lock of the Three Gorges Dam in China.

Occurrence and geochemical behavior of arsenic in a coastal aquifer–aquitard system of the Pearl River Delta, China

Elevated concentrations of arsenic, up to 161 μg/L, have been identified in groundwater samples from the confined basal aquifer underlying the aquitard of the Pearl River Delta (PRD). Both aquatic arsenic in pore water and solid arsenic in the sediments in the basal aquifer and aquitard were identified. Arsenic speciation of groundwater in the basal aquifer was elucidated on a pH-Eh diagram. In the PRD, arsenic is enriched in groundwater having both low and high salinity, and arsenic enriched groundwater is devoid of dissolved oxygen, has negative Eh values, is slightly alkaline, and has abnormally high concentrations of ammonium and dissolved organic carbon, but low concentrations of nitrate and nitrite. Results of geochemical and hydrochemical analyses and sequential extraction analysis suggest that reductive dissolution of iron oxyhydroxide could be one of the important processes that mobilized solid arsenic. We speculate that mineralization of sedimentary organic matter could also contribute to aquatic arsenic. Scanning electron microscope analysis confirms that abundant authigenic pyrite is present in the sediments. Sulphate derived from paleo-seawater served as the important sulfur source for authigenic pyrite formation. Co-precipitation of arsenic with authigenic pyrite significantly controlled concentrations of aquatic arsenic in the coastal aquifer-aquitard system.

Tidal groundwater level fluctuations in L-shaped leaky coastal aquifer system

This paper presents an analytical solution to describe tidal groundwater level fluctuations in a coastal leaky aquifer system bounded by water ‐ land boundaries that form a right angle (referred to as L-shaped coastlines). The system consists of an unconfined aquifer, a confined aquifer and a leaky layer between them. Previously published analytical solutions that discuss only single aquifer constitute a special case of the new solution when the permeability of leaky layer approaches zero. A simple approximate solution without integral is presented. Error analysis and hypothetical example show that the approximate solution has adequate accuracy for both groundwater level prediction and parameter estimation for an L-shaped leaky aquifer system. q 2002 Elsevier Science B.V. All rights reserved.

A nonlinear dynamical model of landslide evolution

A nonlinear dynamical model for the evolution of landslide is proposed. The parameters of this model are obtained through an improved iterative algorithm of inversion developed in the paper. Based on the nonlinear dynamical model and nonlinear dynamical systems (NDS) theory, the approaches to determining the Lyapunov exponents, the predictable timescale and the stability criterion of the evolutional state of landslide are given. A case study of the Xintan slope is presented to illustrate the capability and merit of the nonlinear dynamical model.