Abstract
Studies of solute transport in unconfined coastal aquifers typically neglect oceanic oscillations and assume a static seaward boundary condition defined by the mean annual sea level. In this paper, an image monitoring method is used to establish the quantitative relationship between the concentration of a colored tracer and the hue value of the image. The digital image was used to determine the tracer concentration distribution. Controlled laboratory experiments were conducted to quantitatively study the relationship between the tidal amplitude and the solute transport time and dispersion. Experiments show that the solute transport time is not associated with the tidal amplitude, but only with the average hydraulic gradient between the seaward boundary and the landward boundary. The dispersion range of the solute plume increases with the increase of the tidal amplitude. On large-scale beaches in nature, when the average hydraulic gradient of the aquifer between the sea side and the land side is small enough, the dispersion coefficient is proportional to the tidal amplitude in equal proportion. Therefore, when it comes to the transport time of pollutants, it is possible to set the seaward boundary as the mean annual sea level. In a study of the dispersion range of pollutants, it is inappropriate to set the seaward boundary as the mean annual sea level.
Résumé
Les études du transport de solutés dans les aquifères côtiers à surface libre négligent généralement les oscillations océaniques et font l’hypothèse d’une condition limite statique vers la mer définie par son niveau annuel moyen. Dans cet article, une méthode de suivi d’image est utilisée pour établir la relation quantitative entre la concentration d’un traceur coloré et la valeur de la teinte de l’image. L’image numérique a été utilisée pour déterminer la distribution de la concentration du traceur. Des expériences contrôlées en laboratoire ont été menées pour étudier quantitativement la relation entre l’amplitude de la marée et le temps de transport et la dispersion du soluté. Les expériences montrent que le temps de transport du soluté n’est pas associé à l’amplitude de la marée, mais seulement au gradient hydraulique moyen entre les limites côté mer et côté terre. La gamme de dispersion du panache de soluté augmente avec l’amplitude de la marée. Sur les plages à grande échelle dans la nature, lorsque le gradient hydraulique moyen de l’aquifère entre le côté mer et le côté terre est suffisamment faible, le coefficient de dispersion est proportionnel à l’amplitude de la marée dans la même proportion. Par conséquent, lorsqu’il s’agit du temps de transport des polluants, il est possible de fixer la limite vers la mer au niveau moyen annuel de la mer. Dans une étude de l’étendue de la dispersion des polluants, il est inapproprié de fixer la limite vers la mer au niveau annuel moyen de la mer.
Resumen
Los estudios sobre el transporte de solutos en acuíferos costeros no confinados suelen ignorar las oscilaciones del mar y suponen una condición de contorno estática hacia el mar definida por su nivel medio anual. En este trabajo se utiliza un método de monitoreo de imágenes para determinar la relación cuantitativa entre la concentración de un trazador coloreado y el valor del tono de la imagen. La imagen digital se utilizó para determinar la distribución de la concentración del trazador. Se realizaron experimentos de laboratorio controlados para estudiar cuantitativamente la relación entre la amplitud de la marea y el tiempo de transporte del soluto y la dispersión. Los experimentos muestran que el tiempo de transporte de soluto no está asociado con la amplitud de la marea, sino sólo con el gradiente hidráulico medio entre el límite hacia el mar y el límite hacia tierra. El rango de dispersión de la pluma de soluto aumenta con el incremento de la amplitud de la marea. En las playas de mayor escala en la naturaleza, cuando el gradiente hidráulico medio del acuífero entre el lado del mar y el lado de la tierra es lo suficientemente pequeño, el coeficiente de dispersión es proporcional a la amplitud de la marea en igual proporción. Por lo tanto, cuando se trata del tiempo de transporte de los contaminantes, es posible fijar el límite hacia el mar como el nivel medio anual del mar. En un estudio sobre la amplitud de dispersión de los contaminantes, no es adecuado fijar el límite hacia el mar como el nivel medio anual del mar.
摘要
潜水沿海含水层中的溶质迁移研究通常忽略海洋振荡, 并假设年平均海平面为静态向海边界条件。本文采用图像监测方法, 建立了有色示踪剂浓度与图像色相之间的定量关系。数字图像用于确定示踪剂浓度分布。进行了可控性实内实验, 以定量研究潮汐幅度与溶质迁移时间和弥散度之间的关系。实验表明, 溶质运移时间与潮位无关, 只与向海边界和向陆边界的平均水力梯度有关。溶质羽的弥散范围随着潮幅的增大而增大。在自然界的大尺度海滩上, 当海侧和陆侧之间含水层的平均水力梯度足够小时, 弥散系数与潮幅等比例成正比。因此, 在污染物的迁移时间上, 可以将向海边界设为年平均海平面。在研究污染物扩散范围时, 不宜将向海边界设定为年平均海平面。
Resumo
Estudos de transporte de soluto em aquíferos livres costeiros tipicamente negligenciam as oscilações oceânicas e assumem condições de contorno de mar estático definida por uma média anual do nível do mar. Neste artigo, um método de monitoramento por imagem é usado para estabelecer uma relação quantitativa entre a concentração de traçadores corantes e o valor da tonalidade da imagem. A imagem digital foi usada para determinar a distribuição da concentração do traçador. Experimentos laboratoriais controlados foram conduzidos para estudar quantitativamente a relação entre a amplitude da maré e o tempo do transporte de soluto e dispersão. Os experimentos mostraram que o tempo de transporte do soluto não está associado com a amplitude da maré, mas apenas com o gradiente hidráulico médio entre o limite marítimo e o limite terrestre. A variação da dispersão da pluma do soluto aumenta com o aumento da amplitude da maré. Em praias de grande escala na natureza, quando o gradiente hidráulico médio do aquífero entre o lado marítimo e o lado terrestre é pequeno o suficiente, o coeficiente de dispersão é proporcional à amplitude da maré em proporção igual. Portanto, quando se trata do tempo de transporte de poluentes, é possível definir o contorno marítimo com a média anual do nível do mar. No estudo de variações de dispersão de poluentes, é inapropriado para definir o contorno marítimo com a média anual do nível do mar.
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This work was supported by the National Natural Science Foundation of China (No. 42172281) and the Opening Fund of the State Key Laboratory of China University of Geosciences (Wuhan) (No. SKJ2018055).
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Guo, M., Wan, J. & Huang, K. Solute transport characteristics and influencing factors in a coastal unconfined aquifer under tidal action identified by image monitoring in a laboratory experimental setup. Hydrogeol J 30, 989–1004 (2022). https://doi.org/10.1007/s10040-022-02476-7
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DOI: https://doi.org/10.1007/s10040-022-02476-7