Browsing by Author "Chuang, Mo-Hsiung"

Now showing 1 - 9 of 9

A generalized solution for groundwater head fluctuation in a tidal leaky aquifer system
(2011-12-01)
Chuang, Mo-Hsiung
;
Yeh, Hund-Der
;
環境工程研究所
;
Institute of Environmental Engineering
A new analytical solution is developed for describing groundwater level fluctuations in a coupled leaky confined aquifer system which consists of an unconfined aquifer, confined aquifer, and an aquitard in between. The aquifer system has a tidal boundary at the seashore, a no flow boundary at remote inland side, and a confined aquifer extending under the sea and terminated with an outlet-capping. This new solution has shown to be a generalisation of most existing analytical solutions for a tidal aquifer system which includes single confined and leaky confined aquifers. In addition, the solution is used to explore the influences of the dimensionless leakance of the outlet-capping, the dimensionless hydraulic diffusivities, and the leakages of the inland and offshore aquitards on the head responses in the leaky confined aquifer.
A perturbation solution for head fluctuations in a coastal leaky aquifer system considering water table over-height
(2012)
Chuang, Mo-Hsiung
;
Mahdi, Asadi-Aghbolaghi
;
Yeh, Hund-Der
;
環境工程研究所
;
Institute of Environmental Engineering
This paper develops a new analytical solution for the aquifer system, which comprises an unconfined aquifer on the top, a semi-confined aquifer at the bottom and an aquitard between them. This new solution is derived from the Boussinesq equation for the unconfined aquifer and one-dimensional leaky confined flow equation for the lower aquifer using the perturbation method, considering the water table over-height at the remote boundary. The head fluctuation predicted from this solution is generally greater than the one solved from the linearized Boussinesq equation when the ratio of the tidal amplitude to the thickness of unconfined aquifer is large. It is found that both submarine groundwater discharges from upper and lower aquifers increase with tidal amplitude-aquifer thickness ratio and may be underestimated if the discharge is calculated based on the average head fluctuation. The effects of the aquifer parameters and linearization of the Boussinesq equation on the normalized head fluctuation are also investigated.
An Analytical Solution of Groundwater Flow in Wedge-shaped Aquifers with Estuarine Boundary Conditions
(2018-12-01)
Chuang, Mo-Hsiung
;
Yeh, Hund-Der
;
環境工程研究所
;
Institute of Environmental Engineering
The issue of the groundwater fluctuation due to tidal effect in a two-dimensional coastal leaky aquifer system has attracted much attention in recent years. The predictions of head fluctuation play an important role in dealing with groundwater managements and contaminant remediation problems in costal aquifers. This article presents a two-dimensional analytical model describing the groundwater flow in a coastal leaky aquifer of wedge shape affected by the tides and bounded by two estuarine rivers with an arbitrary included angle. The solution of the model is derived in the Polar coordinates by the Hankel transform and finite sine transform. The head fluctuation predicted by this new solution is compared with that by an existing solution for groundwater flow in a non-L shaped tidal aquifer. The groundwater fluctuation due to the joint effect of estuarine tides is explored based on the present solution. Moreover, the influences of the parameters such as diffusion (D-i), included angle (?), and tidal river coefficients (K-1, K-2) on the head fluctuation in the aquifer are also assessed and discussed. The results demonstrate that those parameters have significant effects on the head fluctuation in the leaky confined aquifer system. Moreover, the effect of D-i increases with ?, and the effects of K-1 and K-2 on the normalized amplitude and phase lag of the groundwater fluctuation are significant when both parameter values are larger than 10(-5).
Groundwater response to tidal fluctuation in a sloping leaky aquifer system
(2012-10-01)
Asadi-Aghbolaghi, Mahdi
;
Chuang, Mo-Hsiung
;
Yeh, Hund-Der
;
環境工程研究所
;
Institute of Environmental Engineering
The effect of tidal fluctuation on groundwater flow is an important issue from many aspects in coastal areas. This paper develops a new analytical solution to describe the groundwater fluctuation in a sloping coastal aquifer system which comprises an upper unconfined aquifer, a lower confined aquifer, and an aquitard in between. The solution is allowed to investigate the effects of bottom slope and leakage as well as aquifer parameters on head fluctuations in both unconfined and confined aquifers. The research result indicates that the effect of the bottom angle on the groundwater fluctuation and time lag is significant in the unconfined aquifer and not negligible if the leakage in the confined aquifer is large. In addition, the joint effects of aquifer parameters and bottom angle on groundwater fluctuation and time lag are also discussed. (C) 2011 Elsevier Inc. All rights reserved.
Groundwater Response to Tidal Fluctuation in an Inhomogeneous Coastal Aquifer-Aquitard System
(2014-09-01)
Asadi-Aghbolaghi, Mahdi
;
Chuang, Mo-Hsiung
;
Yeh, Hund-Der
;
環境工程研究所
;
Institute of Environmental Engineering
This paper investigates tide-induced groundwater fluctuation and submarine groundwater discharge (SGD) in a leaky inhomogeneous coastal aquifer system with an upper unconfined aquifer, a lower confined aquifer, and an aquitard between them. The upper left aquifer is formed due to land reclamation. The SGD defined as the groundwater flow from land into the sea is controlled mainly by the hydraulic gradient between land and sea. An analytical expression is developed to discuss and assess the effect of inhomogeneity on the groundwater head fluctuation in the leaky aquifer system. Joint effects of aquifers\' parameters such as leakage and hydraulic diffusivity on the groundwater head fluctuation and SGD are investigated. The predicted results from the analytical expression indicate that the groundwater head fluctuation in both unconfined and confined aquifers is dependent on dimensionless leakages and increases with dimensionless hydraulic diffusivity.
Groundwater Response to Tidal Fluctuation in an Inhomogeneous Coastal Aquifer-Aquitard System
(2014-09-01)
Asadi-Aghbolaghi, Mahdi
;
Chuang, Mo-Hsiung
;
Yeh, Hund-Der
;
環境工程研究所
;
Institute of Environmental Engineering
This paper investigates tide-induced groundwater fluctuation and submarine groundwater discharge (SGD) in a leaky inhomogeneous coastal aquifer system with an upper unconfined aquifer, a lower confined aquifer, and an aquitard between them. The upper left aquifer is formed due to land reclamation. The SGD defined as the groundwater flow from land into the sea is controlled mainly by the hydraulic gradient between land and sea. An analytical expression is developed to discuss and assess the effect of inhomogeneity on the groundwater head fluctuation in the leaky aquifer system. Joint effects of aquifers' parameters such as leakage and hydraulic diffusivity on the groundwater head fluctuation and SGD are investigated. The predicted results from the analytical expression indicate that the groundwater head fluctuation in both unconfined and confined aquifers is dependent on dimensionless leakages and increases with dimensionless hydraulic diffusivity.
Spectral analysis of temporal variability of nonlinear and nonstationary rainfall-runoff processes
(2019-08-01)
Chang, Ching-Min
;
Yeh, Hund-Der
;
Chuang, Mo-Hsiung
;
環境工程研究所
;
Institute of Environmental Engineering
This study deals with the time-dependent nonlinear response of catchments to the variations in rainfall. Both the rainfall and runoff discharge fields are treated to be nonstationary in time. A functional series representation, a generalization of the linear convolution integral, is employed to quantify the nonlinear relation between the input and output. The Fourier-Stieltjes representation approach is used to evaluate the variance of runoff discharge in the spectral frequency domain. The analysis based on the spectral solution for the runoff discharge variance clearly demonstrates that larger values of rainfall characteristic time scale or catchment size parameter lead to larger variability of the runoff discharge, while a larger catchment scale parameter leads to smaller variability of the runoff discharge.
Temporal Variability in the Response of a Linear Time-Invariant Catchment System to a Non-Stationary Inflow Concentration Field
(2020-08-01)
Chang, Ching-Min
;
Ma, Kuo-Chen
;
Chuang, Mo-Hsiung
;
環境工程研究所
;
Institute of Environmental Engineering
Predicting the effects of changes in dissolved input concentration on the variability of discharge concentration at the outlet of the catchment is essential to improve our ability to address the problem of surface water quality. The goal of this study is therefore dedicated to the stochastic quantification of temporal variability of concentration fields in outflow from a catchment system that exhibits linearity and time invariance. A convolution integral is used to determine the output of a linear time-invariant system from knowledge of the input and the transfer function. This work considers that the nonstationary input concentration time series of an inert solute to the catchment system can be characterized completely by the Langevin equation. The closed-form expressions for the variances of inflow and outflow concentrations at the catchment scale are derived using the Fourier-Stieltjes representation approach. The variance is viewed as an index of temporal variability. The closed-form expressions therefore allow to evaluate the impacts of the controlling parameters on the temporal variability of outflow concentration.
Tide-induced groundwater level fluctuation in a U-shaped coastal aquifer
(2015-11-01)
Huang, Fu-Kuo
;
Chuang, Mo-Hsiung
;
Wang, Grace S.
;
Yeh, Hund-Der
;
環境工程研究所
The prediction of groundwater level fluctuation due to tidal waves propagation in coastal aquifers is important for the planning and management of water resources in coastal areas. A two-dimensional (2-D) analytical solution is derived to describe the tidal groundwater fluctuation in an aquifer bounded by three water-land boundaries that form a U-shaped coastline. Two opposite sides represent estuary-land boundaries on which the amplitude attenuation and phase shift of the tidal movement in the estuary are considered while the third side is an ocean-land boundary. The effects of wave interaction due to the propagation of oscillating oceanic tides in the cross-shore direction inland and the transmission of the two opposite estuarine tides in the along-shore direction are investigated. Three existing head-fluctuation solutions can be considered as special cases of the present solution; one is for one-dimensional flow and the other two are for 2-D flow. A transition distance ranging from 10 to 15 times of tidal propagation length along the shoreline can be estimated based on the solution. This distance can be used to judge whether the interaction among tides is significant. The influences of hydraulic properties on the tidal fluctuations within the aquifer can therefore be assessed quantitatively. Based on sensitivity analyses, one can conclude that the tidal head is most sensitive to the transmissivity and storativity of the aquifer, and least to the damping coefficient of tidal amplitude and wave number along the estuary. The sensitivities of head fluctuation to the changes of transmissivity and storativity depend on the shoreline length and whether the interaction among waves is significant. On the other hand, the sensitivities of head fluctuation to the changes of damping coefficient and wave number increase with diagonal distance from the entry of estuary and reach the largest magnitude near the estuary far away seashore. (C) 2015 Elsevier B.V. All rights reserved.