Qiaona Guo

Hydrodynamics in a gravel beach and its impact on the Exxon Valdez oil

[1]xa0This paper investigated the interaction of groundwater and seawater in a tidally influenced gravel beach. Field observations of water table, pore water salinity were performed. The two-dimensional finite element model MARUN was used to simulate observed water table and salinity. Based on field observations and model calibrations, a two-layered beach structure was identified which is characterized by a high-permeability surface layer underlain by a low-permeability lower layer. The salt wedge seaward of the low tide line was almost invariant in comparison with the strong fluctuations of the salinity plume in the surface layer of the intertidal zone. The presence of the two layers prevented the presence of a freshwater discharge “tube” between the upper saline plume and salt wedge. This is in contrast with the previous works where freshwater discharge tube was observed. The tide-induced submarine groundwater discharge (SGD) was estimated at 9 m3 d−1 m−1, a large value that is probably due to the large tidal range of ∼4.8 m and the very permeable surface layer. The freshwater-seawater dynamics revealed here may provide new insights into the complexity, intensity, and time scales of mixing between fresh groundwater and seawater in tidal beaches. The simulated water table of the beach was higher than the interface between the surface layer and the lower layer, which prevented Exxon Valdez oil from penetrating into the lower layer in 1989.

Modeling Flow and Solute Transport in Fractured Porous Media at Jinping I-Hydropower Station, China

AbstractA model that couples the rock matrix and fracture flow is employed to simulate the flow and solute transport in fractured porous media. The porous matrix is represented using an equivalent continuum model, and discrete fractures are described using a discrete-fracture network model. Data on the fracture properties were collected from the study area to randomly generate the fractures. The model was calibrated and validated using the measured groundwater levels and tracer test data. The results indicate that the groundwater levels and concentrations simulated using the coupled model agree well with the observed data. In contrast, those obtained using the continuum model for the entire domain do not. In the fracture areas in which abnormal groundwater levels were observed (i.e.,xa0where the level was lower than the Yalong River stage), the coupled model effectively captures and replicates the primary geological and hydrogeological characteristics. Once again, the continuum model results do not. A sensi...

Spatial and temporal variability of the chemistry of the shallow groundwater in the alluvial fan area of the Luanhe river, North China

Groundwater in the alluvial fan area of the Luanhe river, north China, was monitored every 2xa0months for a year. Subsequently, the temporal and spatial variability in the hydrochemical characteristics of the water was investigated using hierarchical cluster analysis (HCA) and a trilinear Piper diagram. It is found that the spatial variability in the groundwater composition from different monitoring wells has obvious differences, even if the distance between many of the wells is small. Also, the difference in the ion concentration was found to be up to fivefold for the same monitored well. Research has indicated that the groundwater’s chemical characteristics are mainly controlled by soil type, the amount of precipitation, the Luanhe river, the groundwater, and human factors. The thickness and continuous distribution of clay influences the velocity and ion exchange rate of the groundwater flow. This results in the amount of total dissolved solids in the groundwater increasing from upstream to downstream. In the flood season (June, July, and August), ion concentration gradually decreases as a result of the increased recharging of the groundwater due to precipitation. Classification using HCA indicates that the samples can be clustered into different groups according to correlation coefficients. Also, the chemical composition of the water from monitoring wells near the Luanhe river is approximately consistent with that from the Luanhe river. This implies that the samples have some compositions resulted from the mixing of groundwater and river water. The Piper diagram indicates that Ca2+, Mg2+, and HCO3− ions are the predominant ones present, i.e., the type of groundwater is of the Ca–Mg–HCO3 type.

Estimating hydraulic parameters of a heterogeneous aquitard using long-term multi-extensometer and groundwater level data

The classical aquitard-drainage model COMPAC has been modified to simulate the compaction process of a heterogeneous aquitard consisting of multiple sub-units (Multi-COMPAC). By coupling Multi-COMPAC with the parameter estimation code PEST++, the vertical hydraulic conductivity (Kv) and elastic (Sske) and inelastic (Sskp) skeletal specific-storage values of each sub-unit can be estimated using observed long-term multi-extensometer and groundwater level data. The approach was first tested through a synthetic case with known parameters. Results of the synthetic case revealed that it was possible to accurately estimate the three parameters for each sub-unit. Next, the methodology was applied to a field site located in Changzhou city, China. Based on the detailed stratigraphic information and extensometer data, the aquitard of interest was subdivided into three sub-units. Parameters Kv, Sske and Sskp of each sub-unit were estimated simultaneously and then were compared with laboratory results and with bulk values and geologic data from previous studies, demonstrating the reliability of parameter estimates. Estimated Sskp values ranged within the magnitude of 10−4xa0m−1, while Kv ranged over 10−10–10−8xa0m/s, suggesting moderately high heterogeneity of the aquitard. However, the elastic deformation of the third sub-unit, consisting of soft plastic silty clay, is masked by delayed drainage, and the inverse procedure leads to large uncertainty in the Sske estimate for this sub-unit.RésuméLe modèle classique de drainage d’un aquitard COMPAC a été modifié afin de simuler les processus de compaction d’un aquitard hétérogène en multiples sous-unités (Multi-COMPAC). En couplant Multi-COMPAC avec le code PEST++ d’estimation de paramètres, la conductivité hydraulique verticale (Kv) et les valeurs de capacité spécifique du squelette élastique (Sske) et non élastique (Sskp) de chaque sous-unité peuvent être estimées en utilisant des données observées de multi-extensomètre et piézométriques de longue durée. L’approche a été tout d’abord testée pour un cas synthétique avec des paramètres connus. Les résultats de ce cas synthétique montrent qu’il est. possible d’estimer de manière précise les trois paramètres pour chaque sous-unité. Ensuite, la méthodologie a été appliquée à un site localisé dans la ville de Changzhou en Chine. A partir d’information détaillée stratigraphique et de données d’extensomètre, l’aquitard a été subdivisé en trois sous-unités. Les paramètres Kv, Sske et Sskp de chaque sous-unité ont été estimés simultanément et puis ont été comparés avec des résultats de laboratoire, ainsi qu’avec des valeurs brutes et de données géologiques d’études antérieures, démontrant la fiabilité des estimations des paramètres. Les valeurs estimées de Sskp sont comprises au sein d’une gamme de 10−4xa0m−1, alors que Kv est. comprise entre 10−10–10−8xa0m/s, suggérant une hétérogénéité modérément élevée de l’aquitard. Cependant, la déformation élastique de la troisième sous-unité, constituée d’argile silteuse plastique molle, est. masquée par une drainage différée, et la procédure d’inversion conduit à une grande incertitude dans l’estimation de Sske pour cette sous-unité.ResumenSe modificó el clásico modelo de drenaje de acuitardos COMPAC para simular el proceso de compactación de un acuitardo heterogéneo compuesto por múltiples subunidades (Multi-COMPAC). Mediante el acoplamiento de Multi-COMPAC con el código de estimación de parámetros PEST++, se pueden estimar los valores de conductividad hidráulica vertical (Kv) y elástica (Sske) e inelástica (Sskp) de cada subunidad utilizando las observaciones de un multi-extensómetro y datos de niveles de agua subterránea a largo plazo. El enfoque se probó primero a través de un caso sintético con parámetros conocidos. Los resultados del caso sintético revelaron que era posible estimar con precisión los tres parámetros para cada subunidad. A continuación, se aplicó la metodología a un sitio de campo ubicado en la ciudad de Changzhou, China. Basándose en la información estratigráfica detallada y en los datos del extensómetro, el acuitardo de interés se subdividió en tres subunidades. Los parámetros Kv, Sske y Sskp de cada subunidad se estimaron simultáneamente y luego se compararon con los resultados de laboratorio y con los valores y los datos geológicos de estudios anteriores, lo que demuestra la fiabilidad de los parámetros estimados. Los valores estimados de Sskp oscilaron dentro de la magnitud de 10−4xa0m−1, mientras que Kv osciló entre 10−10–10−8xa0m/s, lo que sugiere una heterogeneidad moderadamente alta del acuitardo. Sin embargo, la deformación elástica de la tercera subunidad, que consiste en arcilla limosa plástica blanda está enmascarada por el drenaje retardado, y el procedimiento inverso conduce a una gran incertidumbre en la estimación de Sske para esta subunidad.摘要对传统的弱透水层-排水模型COMPAC进行了改进,用来模拟一个含多重亚单元的非均质质弱透水层的压缩过程(Multi-COMPAC)。通过Multi-COMPAC与参数估算程序PEST++相耦合,利用观测的长期多重分层标和地下水位资料,可以估算每一个亚单元的垂直渗透系数(Kv)和弹性(Sske)以及非弹性(Sskp)贮水率。该方法首先通过数值试验进行验证,结果显示,每一个亚单元的这三个参数都可以被精确估计。然后,该方法应用到了中国常州市的一个野外试验点。根据详细的地层信息和分层标数据,所研究的 弱透水层被分为三个亚单元。估算了每个亚单元的参数Kv、 Sske 和Sskp后与室内试验结果和过去研究中得到的平均值以及地质资料进行了对比,证明了参数估算结果的可靠性。估算的Sskp值在10−4xa0m−1量级以内,而Kv在10−10–10−8xa0m/s量级内变化,表明弱透水层具有较高的非均质性。然而,由松软的塑性粉质粘土构成的第三个亚单元的弹性变形被滞后排水所隐藏,反演过程显示本亚单元Sske的估算值具有很大的不确定性。ResumoO clássico modelo COMPAC para drenagem de aquitarde foi modificado para simular o processo de compactação de um aquitarde heterogêneo composto por múltiplas unidades (Multi-COMPAC). Por meio do acoplamento do Multi-COMPAC com o código de estimativa de parâmetros PEST ++, os valores de condutividade hidráulica vertical (Kv) e da capacidade específica elástica (Sske) e inelástica (Sskp) podem ser estimados para cada unidade utilizando uma série de dados de multiextensômetro e de nível de água. A abordagem foi primeiramente testada em um caso sintético com parâmetros conhecidos. Os resultados do caso sintético revelaram que era possível estimar com precisão os três parâmetros para cada unidade. Em seguida, o método foi aplicado a campo, em uma área localizada na cidade de Changzhou, China. Com base na estratigrafia detalhada e nos dados do extensômetro, o aquitarde de interesse foi subdividido em três unidades estratigráficas. Os parâmetros Kv, Sske e Sskp de cada unidade foram estimados simultaneamente e depois comparados com os resultados laboratoriais e com diversos valores e dados geológicos de estudos anteriores, demonstrando a confiabilidade das estimativas dos parâmetros. Os valores de Sskp estimados variaram dentro da magnitude de 10−4xa0m−1, enquanto Kv variou de 10−10–10−8xa0m/s, sugerindo uma heterogeneidade moderadamente elevada do aquitarde. No entanto, a deformação elástica da terceira unidade, composta por argila-siltosa levemente plástica, é mascarada pela drenagem tardia e o procedimento inverso leva a grande incerteza na estimativa de Sske para esta subunidade.

Scale effect and value criterion of the permeability of the interlayer staggered zones in the basalt of Jinsha River basin, China

The hydrogeological characteristics of structural planes are different to those of the associated bedrock. The permeability, and therefore hydraulic conductivity (K), of a structural plane can be significantly different at different scales. The interlayer staggered zones in the Emeishan Basalt of early Late Permian were studied; this formation is located in the Baihetan hydropower project area in Jinsha River Basin, China. The seepage flow distribution of a solid model and two generalized models (A and B) were computed using COMSOL. The K values of the interlayer staggered zones for all three models were calculated by both simulation and analytical methods. The results show that the calculated K results of the generalized models can reflect the variation trend of permeability in each section of the solid model, and the approximate analytical calculation of K can be taken into account in the calculation of K in the generalized models instead of that found by simulation. Further studies are needed to investigate permeability variation in the interlayer staggered zones under the condition of different scales, considering the scaling variation in each section of an interlayer staggered zone. The permeability of each section of an interlayer staggered zone presents a certain degree of dispersivity at small scales; however, the permeability values tends to converge to a similar value as the scale of each section increases. The regularity of each section of the interlayer staggered zones under the condition of different scales can provide a scientific basis for reasonable selection of different engineering options.RésuméLes caractéristiques hydrogéologiques de plans structuraux sont différentes de celles de la formation au sein de laquelle ils sont interstratifiés. La perméabilité (ou conductivité hydraulique K) d’un plan structural peut-être significativement différente à diverses échelles. Les zones intercoulées décalées du basalte Emeishan du début du Permien Terminal ont été étudiées; cette formation se situe dans la zone du projet hydroélectrique de Baihetan dans le bassin de la rivière Jinsha, Chine. La distribution des flux de suintement issue d’un modèle solide et de deux modèles généralisés (A et B) a été calculée en utilisant COMSOL. Les valeurs de K des zones intercoulées décalées ont été calculées pour les trois modèles à la fois par des méthodes de simulation numérique et des méthodes analytiques. Les résultats montrent que les K calculées avec les modèles généralisés peuvent bien refléter la tendance de variation de la perméabilité dans chaque partie du modèle solide; ils montrent aussi que le calcul analytique approché de K peut être pris en compte pour le calcul de K dans les modèles généralisés à la place des valeurs trouvées par simulation numérique. Des études complémentaires sont nécessaires pour étudier la variation de la perméabilité dans les zones intercoulées décalées pour différentes conditions d’échelle, en considérant la variation d’échelle dans chaque partie d’une zone intercoulée dispersée. La perméabilité de chaque partie d’une zone intercoulée dispersée présente une certaine dispersion aux petites échelles; cependant, les valeurs de perméabilité tendent à converger vers une valeur similaire lorsque l’échelle de chaque partie augmente. La régularité de chaque partie des zones intercoulées décalées, sous différentes conditions d’échelles, peut fournir une base scientifique pour la sélection raisonnable de différentes options d’ingénierie.ResumenLas características hidrogeológicas de los planos estructurales son diferentes a las de la roca madre asociada. La permeabilidad, y por lo tanto la conductividad hidráulica (K), de un plano estructural puede ser significativamente diferente en distintas escalas. Se estudiaron las zonas intercaladas entre las capas en el basalto Emeishan de principios del Pérmico tardío; esta formación se encuentra en el área del proyecto hidroeléctrico de Baihetan en la cuenca del río Jinsha, China. La distribución del flujo de filtración de un modelo sólido y dos modelos generalizados (A y B) se calcularon utilizando COMSOL. Los valores de K de las zonas intercaladas entre las capas para los tres modelos se calcularon mediante métodos de simulación y analíticos. Los resultados muestran que los resultados K calculados de los modelos generalizados pueden reflejar la tendencia de variación de la permeabilidad en cada sección del modelo sólido, y el cálculo analítico aproximado de K se puede tener en cuenta en el cálculo de K en los modelos generalizados en lugar de aquellos que se encuentra por simulación. Se necesitan más estudios para investigar la variación de la permeabilidad en las zonas intercaladas entre las capas bajo la condición de diferentes escalas, considerando la variación de escala en cada sección de una zona intercalada entre capas. La permeabilidad de cada sección de una zona intercalada entre capas presenta un cierto grado de dispersividad a escalas pequeñas; sin embargo, los valores de permeabilidad tienden a converger a un valor similar a medida que aumenta la escala de cada sección. La regularidad de cada sección de las zonas intercaladas entre capas bajo la condición de diferentes escalas puede proporcionar una base científica para la selección razonable de diferentes opciones de ingeniería.摘要结构面的水文地质特征与相关基岩的水文地质特征不同。结构面的渗透率以及水力传导率(K)在不同尺度上会大不相同。研究了晚二叠世早期峨眉山玄武岩互层交错带;这个地层位于中国金沙江流域白鹤滩水电项目区。利用COMSOL计算了实体模型和两个概化模型的渗流分布。通过模拟和解析方法计算了所有三个模型互层交错带的K值。结果显示,概化模型计算的K结果可反映出实体模型每个截面的渗透率变化趋势,在概化模型中计算k可考虑k的大概解析计算结果,而不用模拟中发现的结果。鉴于互层交错带每个截面的尺度变化,需要进行进一步的研究来调查不同尺度条件下互层交错带的渗透率变化。互层交错带每个截面的渗透率在小尺度上展现出一定程度的弥散性,然而,随着每个截面尺度的增加,渗透率值趋于收敛成类似的值。在不同尺度条件下,互层交错带每个截面的规律性可为不同工程的合理选择提供科学依据。ResumoAs características hidrogeológicas de planos estruturais são diferentes daquelas associadas ao acamamento. A permeabilidade, e consequentemente a condutividade hidráulica (K), de um plano estrutural pode ser significativamente diferente em diferentes escalas. Foram estudadas as zonas intracamadas intercaladas no Basalto de Permiano Tardio inicial de Emeishan; esta formação está localizada na área hidrelétrica de Baihetan na Bacia do Rio Jinsha, China. A distribuição de fluxo de infiltração de um modelo sólido e dois outros modelos generalizados (A e B) foram gerados usando COMSOL. Os valores de K das zonas intracamadas intercaladas para os três modelos foram calculados usando ambos os métodos: simulação e analítico. Os resultados mostram que os K calculados dos modelos generalizados podem refletir a variação de tendência da permeabilidade em cada seção do modelo sólido, e a aproximação de cálculo analítico do K pode ser levado em consideração no cálculo de K em modelos generalizados ao invés do encontrado por simulação. São necessários estudos mais aprofundados para a investigação da variação de permeabilidade das zonas intracamadas intercaladas sob a condição de diferentes escalas, considerando a variação de escala em cada seção de uma zona intracamada intercalada. A permeabilidade de cada seção de uma zona intracamada intercalada apresenta certo grau de dispersão em escalas pequenas; no entanto, os valores de permeabilidade tendem a convergir para um valor similar na medida em que a escala de cada seção aumenta. A regularidade de cada seção de zonas intracamadas intercaladas sob a condição de diferentes escalas pode proporcionar uma base científica para uma seleção razoável de opções no campo da engenharia.

Contaminant transport in a small deformation aquitard affected by the delayed drainage phenomenon

This paper presents a formulation accounting for the effect of Delayed Drainage Phenomenon (DDP) on the breakthrough of contaminant flux in an aquitard, by considering the movement of soil particles, porosity variation, hydraulic head variation and transient flow during the consolidation. The water flow equation in an aquitard was based on the Terzaghis consolidation theory, and the contaminant transport equation was derived on the basis of the mass balance law. Two cases were used to illustrate the effect of DDP on the contaminant transport in an aquitard of small deformation. It is found that the breakthrough time of contaminant in an aquitard is very long, which is mainly ascribed to the low permeability of aquitard and sorption of soil particles. It is also found that the increase of depletion, which is in general induced by the increase of thickness and specific storativity, and the decrease of hydraulic conductivity, enhance the impact of DDP on the contaminant transport in an aquitard. A larger delay index (τ0) of DDP gives a greater Delay Breakthrough Time (DBT) of solute transport in an aquitard, which controls the difference of the breakthrough time of contaminant transport in aquitards with and without the occurrence of DDP. For the cases where advection plays a dominant role during the process of solute transport, τ0 is almost linearly correlated with DBT, and the ratio of DBT over the breakthrough time without consideration of DDP also approximately shows a linear relationship with the ratio of specific storativity to porosity, given a fixed drawdown in the adjacent aquifer with the sorption being ignored.

A field experiment and numerical modeling of a tracer at a gravel beach in Prince William Sound, Alaska

Oil from the 1989 Exxon Valdez oil spill persists in many gravel beaches in Prince William Sound (Alaska, USA), despite great remedial efforts. A tracer study using lithium at a gravel beach on Knight Island, Prince William Sound, during the summer of 2008 is reported. The tracer injection and transport along a transect were simulated using the two-dimensional numerical model MARUN. Model results successfully reproduced the tracer concentrations observed at wells along the transect. A sensitivity analysis revealed that the estimated parameters are well determined. The simulated spatial distribution of tracer indicated that nutrients applied along the transect for bioremediation purposes would be washed to the sea very quickly (within a semi-diurnal tidal cycle) by virtue of the combination of the two-layered beach structure, the tidal fluctuation and the freshwater flow from inland. Thus, pore-water samples in the transect were found to be clean due to factors other than bioremediation. This may explain why the oil did not persist within the transect.RésuméDe l’huile issue de l’accident de la compagnie pétrolière Exxon Valdez en 1989 persiste dans de nombreuses plages de gravier dans le Prince William Sound (Alaska, Etats Unis d’Amérique), malgré les grands efforts de remédiation. Un traçage utilisant du lithium réalisé durant l’été 2008 dans la plage de gravier de l’île Knight, dans le Prince William Sound est présenté. L’injection du traceur et le transport le long d’une coupe ont été simulés en utilisant le modèle numérique bidimensionnel MARUN. Les résultats du modèle reproduisent avec succès les concentrations du traceur observés dans des puits le long de la coupe. Une analyse de sensibilité a révélé que les paramètres estimés sont bien déterminés. La distribution spatiale simulée du traceur indique que les substances nutritives appliquées le long de la coupe pour les besoins de la remédiation seraient éliminées vers la mer très rapidement (selon un cycle de marée semi diurne) résultant de l’action combinée de la structure à deux couches de la plage, les fluctuations de la marée et l’apport d’eau douce de l’intérieur des terres. Ainsi, des échantillons d’eau porale dans la coupe se sont avérées être une eau propre à cause de facteurs autre que ceux liés à la bioremédiation. Cela peut expliquer pourquoi l’huile ne persiste pas au sein de la coupe.ResumenEl petróleo del derrame del Exxon Valdez en 1989 persiste en muchas playas de grava en Prince William Sound (Alaska, EE.UU.), a pesar de los grandes esfuerzos de remediación. Se informa un estudio de trazador usando litio en la playa de grava en Knight Island, Prince William Sound, durante el verano de 2008. La inyección del trazador y el transporte a lo largo de una transecta se simularon usando el modelo numérico bidimensional MARUN. Los resultados del modelo reprodujeron exitosamente las concentraciones del trazador observadas en los pozos a lo largo de la transecta. Un análisis de sensibilidad reveló que los parámetros estimados están bien determinados. La distribución especial simulada del trazador indicó que los nutrientes aplicados a lo largo de la transecta para propósitos de biorremediación podrían ser lavados hacia el mar muy rápidamente (dentro de un ciclo mareal semidiurno) en virtud de la combinación de la estructura de dos capas de la playa, la fluctuación de marea y el flujo de agua dulce desde el continente. Así, se encontró que las muestras del agua poral en la transecta están bien limpias debido a factores diferentes a la biorremediación. Esto puede explicar porque el petróleo no persistió dentro de la transecta.摘要尽管采取了很大的补救措施, 但1989年埃克森瓦尔迪兹石油公司漏油事件中的油仍然存在于 (美国阿拉斯加州) 威廉王子海峡的许多砾石海滩中. 2008年夏天在威廉王子海峡骑士岛的砾石海滩利用锂进行了示踪研究. 采用二维数值模型MARUN模拟了示踪剂沿横断面的注入和传输过程. 模型成功地再现了沿横断面观测井观测到的示踪剂含量. 灵敏度分析显示, 估算的参数很好地得到确定. 示踪剂模拟的空间分布表明, 沿横断面应用的用于生物修复目的的营养素凭借两层的海滩结构—潮汐波动和来自内陆的淡水流会很快 (在半日的潮汐周期内) 被冲到大海. 因此, 发现横断面的孔隙水样由于影响因素而非生物修复显得很干净. 这可解释为什么油没有存留在横断面内.ResumoApesar dos esforços de remediação, o petróleo do derrame de petróleo de 1989 do Exxon Valdez persiste em muitas praias de Prince William Sound (Alasca, EUA). É reportado um estudo com traçadores, com uso do lítio, numa praia de seixo da Ilha Knight, em Prince William Sound, durante o verão de 2008. A injeção do traçador e o transporte ao longo de um transecto foram simulados através do uso do modelo numérico bidimensional MARUN. Os resultados do modelo reproduziram com sucesso as concentrações do traçador observadas em furos ao longo do transecto. Uma análise de sensibilidade revelou que os parâmetros estimados foram bem determinados. A simulação da distribuição espacial do traçador indicou que os nutrientes aplicados ao longo do transecto com o propósito de bioremediação seriam muito rapidamente arrastados para o mar (dentro de um ciclo de maré semidiurno) em virtude da combinação da estrutura de duas camadas da praia, da flutuação de maré e do fluxo de água doce a partir do continente. Por esse motivo, amostras de água dos poros dentro do transecto foram encontradas limpas devido a fatores que não têm que ver com a bioremediação. Isto pode explicar porque é que o petróleo não persistiu dentro da zona do transecto.