Hydrogeology Journal

, Volume 18, Issue 1, pp 95–105 | Cite as

Dynamics of negative hydraulic barriers to prevent seawater intrusion

Paper

Abstract

Negative hydraulic barriers that intercept inflowing saltwater by pumping near the coast have been proposed as a corrective measure for seawater intrusion in cases where low heads must be maintained. The main disadvantage of these barriers is that they pump a significant proportion of freshwater, leading to contamination with saltwater at the well. To minimize such mixing, a double pumping barrier system with two extraction wells is proposed: an inland well to pump freshwater and a seawards well to pump saltwater. A three-dimensional variable density flow model is used to study the dynamics of the system. The system performs very efficiently as a remediation option in the early stages. Long-term performance requires a well-balanced design. If the pumping rate is high, drawdowns cause saltwater to flow along the aquifer bottom around the seawater well, contaminating the freshwater well. A low pumping rate at the seawards well leads to insufficient desalinization at the freshwater well. A critical pumping rate at the seawater well is defined as that which produces optimal desalinization at the freshwater well. Empirical expressions for the critical pumping rate and salt mass fraction are proposed. Although pumping with partially penetrating wells improves efficiency, the critical pumping rates remain unchanged.

Keywords

Seawater intrusion Double pumping barrier Critical pumping rate Groundwater management Salt-water/fresh-water relations 

Dynamique des barrières hydrauliques négatives pour prévenir l’intrusion d’eau de mer

Résumé

Des barrières hydrauliques négatives ont été proposées comme mesures correctives contre l’intrusion marine dans le cas où des charges peu élevées doivent être maintenues. Ces barrières interceptent les venues d’eau salée par des pompages près de la côte. Le principal inconvénient de ces barrières est qu’elles pompent une proportion considérable d’eau douce, entraînant une contamination du puits par l’eau salée. Pour réduire de tels mélanges, il est proposé un système de barrière par double pompage, avec deux puits d’extraction: un puits vers l’intérieur pour pomper l’eau douce et un puits vers la mer pour pomper l’eau de mer. Un modèle tridimensionnel à densité variable est mis en œuvre pour étudier la dynamique de ce système. Le système fonctionne très efficacement comme une solution corrective dans les premiers temps. L’efficacité à long terme nécessite un dimensionnement très équilibré. Si le pompage est important, les rabattements causent un écoulement d’eau salée à la base de l’aquifère autour du puits d’eau de mer, contaminant ainsi le puits d’eau douce. Un pompage faible au puits côté mer conduit à une désalinisation insuffisante du puits d’eau douce. Le débit critique de pompage au puits d’eau de mer est défini comme étant celui pour lequel la désalinisation du puits d’eau douce est optimale. Des formulations empiriques du débit critique de pompage et de la part de la masse de sel sont proposées. Bien que le pompage au moyen de puits à pénétration partielle améliore l’efficacité, les débits critiques de pompage restent inchangés.

Dinámica de las barreras de doble bombeo para prevenir la intrusión marina

Resumen

Una barrera hidráulica negativa es un sistema de corrección de la intrusión marina que consiste en bombear cerca de la costa para interceptar el agua salada. Tiene sentido en lugares donde el nivel deba mantenerse bajo. Su principal desventaja es que también bombean una proporción significativa de agua dulce, que se contamina al mezclarse con agua salada en el propio pozo. Para reducir al mínimo esta mezcla, se propone un sistema de barrera de doble bombeo, con un pozo tierra adentro para bombear el agua dulce y otro costero para bombear el agua salada. En este trabajo se estudia la dinámica del sistema mediante un modelo tridimensional de flujo con densidad variable. En los primeros estadios, el doble bombeo resulta ser muy eficiente como opción de remedio. Sin embargo, a largo plazo, se pueden dar dos situaciones negativas extremas. Si el caudal de bombeo del pozo costero es elevado, se producen descensos generalizados que favorecen el flujo lateral de agua salada en la base del acuífero, contaminando el pozo de agua dulce. Por el contrario, si dicho caudal es bajo, la desalinización del pozo de agua dulce es insuficiente. Ello conduce a la definición de caudal crítico de extracción en el pozo costero como aquel que produce el grado óptimo de desalinización en el pozo de agua dulce. Se obtienen expresiones empíricas para dicho caudal crítico y la salinidad residual en el pozo de agua dulce. La eficacia del sistema mejora si los pozos son parcialmente penetrantes, cosa que no afecta al caudal crítico.

利用负压阻力动力学原理防止海水入侵

摘要

滨海区通过抽水形成的截取流入海水的负水压阻力被认为是解决低水头条件下海水入侵问题较好的校正方法。这些水压阻力方法的主要缺点是抽出了很大比例的淡水进而导致井口处盐水的污染。为了使这种混合作用最小化, 又提出有两个抽水井的双抽水水压阻力系统: 一个内陆井抽取淡水, 一个向海的井抽取盐水。此外, 我们还建立了一个三维的密度可变流模型来研究这个系统的动力学过程。在早期阶段这个系统作为一种补救选择表现得非常有效, 而长期的性能维持则需要一个良好的平衡态设计。如果抽水速率过大, 水位降深导致盐水沿着海水井附近的含水层底部流动, 进而污染淡水井。如果海水井处的抽水速率过低, 则会导致淡水井处的不充分的脱盐作用。海水井处的临界抽水速率定义为使淡水井处脱盐作用达到最佳效果时的速率。一般推荐使用临界抽水速率和盐分质量分数的经验表达式。虽然有部分渗流井的抽水作用能提高效率, 但是临界抽水速率仍然不变。

Dinâmica de barreiras hidráulicas negativas para prevenir intrusão salina

Resumo

Como medida correctiva para a intrusão salina nos casos em que têm que ser mantidas cargas hidráulicas baixas, têm sido propostas barreiras hidráulicas negativas que intersectam a entrada de água salgada através de bombeamento próximo da linha de costa. A principal desvantagem destas barreiras é bombearem uma proporção significativa de água doce, o que conduz à contaminação do poço por água salgada. Para minimizar esta mistura, propõe-se um sistema de barreira de bombeamento duplo, com dois poços de extracção: um poço em terra para bombeamento de água doce e um poço no domínio marinho para bombear água salgada. Para estudar a dinâmica do sistema foi utilizado um modelo tridimensional de fluxo de densidade variável. Como opção de remediação, o sistema funciona com muita eficiência nos primeiros tempos. As boas prestações a longo prazo exigem uma concepção muito equilibrada. Se o bombeamento é elevado, os rebaixamentos provocam o escoamento da água subterrânea salina ao longo da base do aquífero e em torno do poço situado do lado do mar, contaminando o poço de água doce em terra. Um pequeno bombeamento no poço do lado do mar conduz a uma insuficiente dessalinização no poço de água doce. Define-se um caudal crítico de bombeamento no poço do lado do mar, como sendo aquele que produz uma dessalinização óptima no poço de água doce. Propõem-se expressões empíricas para o caudal crítico de bombeamento e para fracção mássica salina. Se bem que o bombeamento com poços parcialmente penetrantes melhore a eficiência, os caudais críticos de bombeamento mantêm-se inalteráveis.

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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  1. 1.Department of Geotechnical Engineering and Geosciences, School of Civil EngineeringTechnical University of CataloniaBarcelonaSpain
  2. 2.Institute of Environmental Assessment and Water Research (IDAEA-CSIC)BarcelonaSpain

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