Namsik Park

Multiphase Approach to the Numerical Solution of a Sharp Interface Saltwater Intrusion Problem

A sharp interface numerical model is developed to simulate saltwater intrusion in multilayered coastal aquifer systems. The model takes into account the flow dynamics of salt water and fresh water assuming a sharp interface between the two liquids. In contrast to previous two-fluid flow models which were formulated using the hydraulic heads of fresh water and salt water as the dependent variables, the present model employs a mixed formulation having one fluid potential and a pseudosaturation as the dual dependent variables. Conversion of the usual sharp interface flow equations for each aquifer to an equivalent set of two-phase flow equations leads to the definitions of pseudosaturation, capillary pressure, and constitutive relations. The desired governing equations are then obtained by connecting neighboring aquifers via vertical leakage. The proposed formulation is based on a Galerkin finite element discretization. The numerical solution incorporates upstream weighting and nonlinear algorithms with several enhanced features, including rigorous treatment of aquitard leakage and well conditions, and a robust Newton-Raphson procedure with automatic time stepping. The present sharp interface numerical model is verified using three test problems involving unconfined, confined, and multilayered aquifer systems and consideration of steady state and transient flow situations. Comparisons of numerical and analytical solutions indicate that the numerical schemes are efficient and accurate in tracking the location, lateral movement, and upconing of the freshwater-saltwater interface.

Reliability Based Design of Water Distribution Networks Using Multi-Objective Genetic Algorithms

This paper outlines a multi-objective genetic algorithm methodology for the design of a water distribution network. In order to obtain the Pareto-front, the objectives: minimization of network cost and maximization of a reliability measure are considered. A new reliability measure, called network resilience, is introduced. This measure tries to provide (i) surplus head above the minimum allowable head at nodes and (ii) reliable loops with practicable pipe diameters. A set of Pareto-optimal solutions is obtained in the search space of cost and network resilience. Genetic algorithms are observed to be poor in handling constraints. To handle constraints in a better way, a constraint handling technique that does not require a penalty coefficient and applicable to water distribution systems is presented. The present model is applied to two example problems, which were widely reported. Comparison of the results has revealed that the network resilience based approach gave better results.

Applicability of a sharp-interface model for estimating steady-state salinity at pumping wells—validation against sand tank experiments

A numerical sharp-interface model of saltwater and freshwater behavior was validated against experiments conducted in two small scale sand tanks. A simple algorithm was proposed to determine saltwater and freshwater withdrawal rates at a pumping well at which a total pumping rate was specified. Model estimates were compared with transient salinity breakthroughs and steady-state salinities of water extracted from pumping wells in the sand tanks. Experimental scenarios included various combinations of freshwater pumping and injection and saltwater pumping. The corresponding Nash-Sutcliffe model efficiency was 0.95, which showed that the agreement between observations and computed results was satisfactory.

An improved sharp-interface model for assessing NAPL contamination and remediation of groundwater systems

Abstract A numerical model is presented for areal analyses of the three-dimensional (3-D) flow behavior of non-aqueous-phase liquids (NAPLs) in groundwater systems. The model is designed for specific application to chemical or petroleum spills and leaks, and remedial design and evaluation of a NAPL-contaminated site. The mathematical formulation is based on vertical integration of the 3-D two-phase flow equations and incorporation of the modified concept of gravity-segregated vertical equilibrium (GSVE) which yields sharp interfaces separating the zones of mobile NAPL and groundwater. History-dependent pseudo constitutive relations are developed for LNAPLs and DNAPLs (light and dense NAPLs) scenarios taking into account the effects of residual saturations. Owing to the sharp-interface assumption, the soil capillary pressure and relative permeability curves are not needed in the evaluation of pseudo functions. Efficient and mass-conservative nonlinear numerical techniques are adopted for solving the governing equations and treating practical boundary conditions which include injection and recovery wells and trenches. Simulation and application examples are provided to demonstrate verification and utility of the model. Numerical results obtained using the sharp-interface modeling approach are compared with analytical solutions and rigorous multiphase numerical solutions that account for vertical flow components and capillary effects. The verification results show the validity of the GSVE modeling assumptions and accuracy of the proposed formulation and computational schemes in predicting the NAPL recovery. The numerical study also indicates that the present model is highly efficient and is thus suitable for preliminary analyses of site-specific problems with limited data and personal computer resources.

Combined analyses of chemometrics and kriging for identifying groundwater contamination sources and origins at the Masan coastal area in Korea

Hydrogeochemical analyses including the basic statistics of chemical components, Piper’s trilinear diagram, and Mazor’s compositional bivariate diagram revealed that the main source and origin of groundwater contamination was seawater intrusion in the study area. However, the other sources and origins of groundwater contamination could be found by the combined analyses of chemometrics and kriging. Cluster analysis was helpful for the classification on the basis of the contamination characteristics of groundwater quality; however, it was not sufficient for the apportionment of groundwater contamination sources. Factor analysis (FA) determined three factors with 81.07% in total variance: Factor 1 for seawater contamination, Factor 2 for nitrate contamination, and Factor 3 for iron contamination. Factor analysis determined the sources of groundwater contamination; however, it could not discover the origins of contaminants except Factor 1. In backward stepwise mode, discriminant analysis decreased the number of parameters from 18 to 6 in discriminating the contaminant type with 96.2% correctness. TDS, Ca, NO3, Mn, Fe, and Br were the most significant parameters for the discrimination of contaminants. Kriging analysis was very useful for the understanding of correlation and similarity between contaminants and factors of FA, and for the investigation of contaminant origins. It also showed that the similarity between factor scores and contaminant concentrations was proportional to the magnitudes of factor loadings for contaminants. This study represented that the combined analyses of chemometrics and kriging were very indispensable to the identification of groundwater contamination sources and origins, as well as for the spatial classification and assessment of groundwater quality.

Analytical Design Curves to Maximize Pumping or Minimize Injection in Coastal Aquifers

Explicit algebraic equations are derived to determine approximate maximum pumping rates or minimum injection rates to limit sea water intrusion to a prespecified distance from the coastline. The equations are based on Stracks (1976) single-potential solution. The maximum pumping rates and minimum injection rates applied at wells with uniform spacing to control the inland movement of the fresh water-salt water interface in a coastal aquifer could be calculated from Stracks (1976) solution without the need of a numerical optimization algorithm. When wells are distributed in a simple fashion, the maximum intrusion location can be identified precisely for pumping cases and approximately for injection cases. For pumping cases, critical points are the limit of allowable salt water intrusion, whereas no such limit exists for injection cases. Once an application site is identified, a series of design curves for pumping and injection rates can be developed for arbitrary intrusion limits. When a user is interested only in the largest pumping rates associated with critical points, one design curve can yield complete information.

Closed-Form Solutions for Steady State Density-Dependent Flow and Transport in a Vertical Soil Column

Closed-form solutions are derived for steady state density-dependent fluid flow and solute transport problems in a one-dimensional vertical soil column. Transport mechanisms considered are advection, molecular diffusion, and velocity-dependent dispersion. Solutions can be obtained for a wide variety of cases. Characteristics of density-dependent solutions, including effects of variations in density and the thickness of transition zones, are investigated for a simple case. Unique features not found in density-independent solutions are observed. Nonuniform concentration profiles with vanishing density effects are also identified.

Impacts of Fresh and Saline Groundwater Development in Sungsan Watershed, Jeju Island

Saline groundwater, in addition to fresh groundwater, is actively developed for inland aqua culture in Jeju Island where groundwater is practically the only source of freshwater. In this work we analyzed impacts of saline and fresh groundwater development on groundwater systems in Sungsan subwatershed in Jeju. A sharp-interface model was used to simulate fresh and saline groundwater flows. Withdrawal of freshwater imparted adverse impacts by lowering groundwater level and inducing saltwater encroachment. Withdrawal of saline water imparted mixed results: on one hand it lowered groundwater level, on the other hand it reduced saltwater encroachments. However, freshwater development lowered groundwater level much more than salinewater development did. Modified Ghyben-Herzberg ratio was developed for a transition zone with finite width. Comparison against observed data resulted in fair agreement.

A comprehensive sharp-interface simulation-optimization model for fresh and saline groundwater management in coastal areas

Both fresh and saline groundwater may be of some value to coastal communities. A comprehensive simulation-optimization model was developed to identify optimal solutions for managing both types of groundwater in coastal areas. The model may be used for conventional management problems of fresh groundwater development and of seawater intrusion control. In addition, the model can be used for problems of concurrent development of fresh and saline/brackish groundwater for beneficial uses. A set of hypothetical examples is given to demonstrate the applicability of the proposed model. In the protection of an over-exploiting freshwater pumping well, the saltwater pumping scheme was less efficient than the freshwater injection scheme. Although the former scheme may be more advantageous in some limited cases, the latter should be considered first as it retains more freshwater in the aquifer. The example of the concurrent development of fresh and brackish groundwater exhibited two different sets of optimal solutions: one with a large amount of freshwater and a small amount of brackish water with high salinity, and the other with a small amount of freshwater and a large amount of brackish water with low salinity.RésuméL’eau souterraine douce tout comme salée peut représenter une certaine valeur pour les communautés côtières. Un modèle complet de simulation et d’optimisation a été développé pour identifier les solutions optimales pour gérer les deux types d’eau souterraine dans les zones côtières. Le modèle peut être utilisé pour les problèmes classiques de gestion d’eau souterraine douce et de contrôle de l’intrusion d’eau de mer. En outre, le modèle peut être utilisé pour les problèmes d’exploitation concurrentielle d’eau souterraine douce et salée/saumâtre à des fins bénéfiques. Un ensemble d’exemples hypothétiques est donné pour démontrer l’applicabilité du modèle proposé. Dans le cas de la protection d’un puits de pompage surexploitant l’eau douce, un scénario de pompage d’eau salée était moins efficace qu’un scénario d’injection d’eau douce. Bien que le scénario précédent peut être plus avantageux dans certains cas limités, le dernier devrait être considéré en premier du fait qu’il favorise la conservation de l’eau douce dans l’aquifère. L’exemple d’une exploitation concurrentielle d’eaux souterraines douces et saumâtres présentait deux ensembles différents de solutions optimales : une avec un grand volume d’eau douce et un faible volume d’eau saumâtre avec une forte salinité, et l’autre avec un faible volume d’eau douce et un grand volume d’eau saumâtre avec une faible salinité.ResumenTanto el agua subterránea dulce como la salada pueden tener algún valor para las comunidades costeras. Se desarrolló un modelo comprensivo de simulación-optimización para identificar soluciones óptimas para la gestión de ambos tipos de aguas subterráneas en las zonas costeras. El modelo puede ser usado para problemas convencionales de manejo de agua subterránea dulce y de control de la intrusión de agua de mar. Además el modelo puede ser usado para problemas de desarrollo concurrente de agua subterránea dulce y salina / salobre para usos útiles. Se da un conjunto de ejemplos hipotéticos para demostrar la aplicabilidad del modelo propuesto. En la protección de un pozo de bombeo de agua dulce sobreexplotado, el esquema de bombeo de agua salada fue menos eficiente que el esquema de inyección de agua dulce. A pesar de que el primer esquema puede tener más ventajas en algunos casos limitados, este último debiera ser considerado primeramente, ya que retiene más agua dulce en el acuífero. El ejemplo del desarrollo concurrente de agua subterránea dulce y salobre exhibió dos diferentes conjuntos de soluciones óptimas: uno con una gran cantidad de agua dulce y una pequeña cantidad de agua salobre con alta salinidad, y el otro con una pequeña cantidad de agua dulce y una gran cantidad de agua salobre con baja salinidad.摘要地下淡水和咸水对沿海地区的社区可能具有一定的价值。开发了一个综合模拟-最优化模型以确定管理沿海地区这两种类型地下水的最佳方法。模型可用于解决地下淡水开发及咸水入侵控制的常规管理问题。另外,模型还可以用于解决地下淡水及咸水/微咸水同时开发利用出现的问题。本文列出了一组假设的例子以展示所述模型的适用性。在保护超采的淡水抽水井过程中,咸水抽水方案不如淡水注入方案效率高。尽管前者方案在一些有限制的情况下可能更有利,但后者方案应当首先给予考虑,因为此方案在含水层中保留了更多的淡水。地下淡水和咸水同时开采的例子展示出两种不同的最佳解决方法:一种是开采大量的淡水和开采少量的高盐度微咸水,另一种是开采少量的淡水和大量的低盐度微咸水。ResumoAmbas águas subterrâneas, doces e salgadas, podem ser de elevada importância para comunidades costeiras. Um modelo abrangente de simulação-otimização foi desenvolvido para identificar soluções ótimas para o gerenciamento de ambos os tipos de agua subterrânea nestas regiões. Este modelo pode ser utilizado para o gerenciamento de problemas típicos de desenvolvimento de recursos hídricos subterrâneos e controle de intrusão de agua salina. Adicionalmente, o modelo pode ser utilizado para problemas de uso concomitante de água doce e salgada para uso proveitoso. Uma série de situações hipotéticas são apresentados para demonstrar a aplicabilidade do modelo proposto. No caso da proteção de um poço de água doce superexplorado, o método de bombeamento de água salina se mostrou menos eficiente do que o método de injeção de água doce. Apesar de o último ser mais vantajoso em alguns casos, o primeiro deveria ser considerado como primeira opção, uma vez que resulta em maior retenção de água doce no aquífero. O exemplo de desenvolvimento concomitante de águas doce e salinas exibiu dois conjuntos de soluções ótimas: um com grande quantidade de água doce e pequena quantidade de água salobra com alto teor de salinidade, e outro com uma pequena quantidade de água doce e grande quantidade de água salobra com baixa salinidade.

Analytical Evaluation of Interference and Ratio of River Water at Riverbank Filtration Pumping Wells

강변여과는 하천 인근에 다수의 관정을 설치하여 하천수의 수질 개선을 추구하는 기술이다. 그런데 다수의 관정이 인접해 있는 경우 관정간의 상호간섭 현상으로 인하여 취수량에 영향을 미친다. 강변 여과 관정의 경우에는 관정이 관망으로 연결되기 때문에 간섭효과의 요인에는 지하수위 강하량 외에도 유량변화에 따른 ...