Abstract
Groundwater pumping has led to extensive water-level declines and seawater intrusion in coastal Los Angeles, California (USA). A SUTRA-based solute-transport model was developed to test the hydraulic implications of a sequence-stratigraphic model of the Dominguez Gap area and to assess the effects of water-management scenarios. The model is two-dimensional, vertical and follows an approximate flow line extending from the Pacific Ocean through the Dominguez Gap area. Results indicate that a newly identified fault system can provide a pathway for transport of seawater and that a stratigraphic boundary located between the Bent Spring and Upper Wilmington sequences may control the vertical movement of seawater. Three 50-year water-management scenarios were considered: (1) no change in water-management practices; (2) installation of a slurry wall; and (3) raising inland water levels to 7.6 m above sea level. Scenario 3 was the most effective by reversing seawater intrusion. The effects of an instantaneous 1-m sea-level rise were also tested using water-management scenarios 1 and 3. Results from two 100-year simulations indicate that a 1-m sea-level rise may accelerate seawater intrusion for scenario 1; however, scenario 3 remains effective for controlling seawater intrusion.
Résumé
L’exploitation des eaux souterraines a conduit à un déclin important du niveau piézométrique ainsi qu’ à une intrusion d’eau de mer au niveau de la zone côtière de Los Angeles, Californie (Etats-Unis d’Amérique). Un modèle de transport de solutés (SUTRA) a été développé afin de tester les conséquences hydrauliques d’un modèle basé sur la stratigraphie séquentielle au niveau de la zone de Dominguez Gap et d’évaluer les effets de scénarios de gestion de la ressource en eau. Le modèle est un modèle bidimensionnel vertical et suit une ligne d’écoulement entre l’Océan Pacifique et la zone de Dominguez Gap. Les résultats indiquent qu’un système de failles récemment identifié joue un rôle dans le transport de l’eau de mer et qu’une limite stratigraphique située entre les séquences stratigraphiques de Bent Spring et de la partie supérieure de Wilmington peut contrôler les mouvements verticaux de l’eau de mer. Trois scénarios de gestion de l’eau pour une durée de 50 ans ont été analysées : (1) pas de changement dans les pratiques actuelles de gestion de la ressource, (2) installation d’une paroi d’étanchéité et (3) augmentation du niveau d’eau continental de7.6 m au dessus du niveau de la mer. Le troisième scénario est le scénario qui a été jugé le plus efficace pour procéder à une inversion du processus d’intrusion saline. Les effets d’une augmentation instantanée de 1 m du niveau de l’océan ont également été testés, en utilisant les scénarios A et 3. Les résultats de deux simulations pour une période d’un siècle indiquent qu’une augmentation d’un mètre du niveau de la mer a pour conséquence une accélération des intrusions salines pour le scenario 1, alors que le scénario 3 permet de garder le contrôle les intrusions d’eau de mer.
Resumen
El bombeo de las aguas subterráneas ha conducido a extensos descensos del nivel freático y la intrusión de agua de mar en la costa de Los Ángeles, California (EEUU).Un modelo (SUTRA) basado en el transporte de solutos fue desarrollado para probar las implicancias hidráulicas de un modelo de secuencia estratigráfica del área de Dominguez Gap para evaluar los efectos de los escenarios de manejo del agua. El modelo es bidimensional, vertical y sigue una línea aproximada de flujo que se extiende desde el Océano Pacífico a través del área Dominguez Gap. Los resultados indican que un sistema de fallas recientemente identificado puede proveer una vía para el transporte de agua de mar y que el límite estratigráfico localizado entre las secuencias Bent Spring y Wilmington superior puede controlar el movimiento vertical del agua de mar. Se consideraron tres escenarios de cincuentas años de manejo del agua: (1) sin cambios en las prácticas de manejo del agua; (2) instalación de una pantalla de hormigón; y (3) elevación tierra adentro de los niveles de agua a 7.6 m por encima del nivel del mar. El escenario 3 fue el más efectivo para revertir la intrusión de agua de mar. Los efectos de un aumento instantáneo del nivel del mar de 1 m también fueron testedos usando los escenarios de manejo del agua 1 y 3. Los resultados de dos simulaciones de 100 años indican que el ascenso de 1 m del nivel del mar puede acelerar la intrusión de agua de mar para el escenario 1, sin embargo, el escenario 3 permanece efectivo para controlar la intrusión de agua de mar.
摘要
抽取地下水已经引起美国加州洛杉矶海岸大范围的水位下降和海水入侵。我们开发了基于SUTRA的溶质运移模型, 来测试多米格斯山谷地区层序地层学模型所预示的水力模式, 并评估不同水管理方案的效果。模型是二维垂向的, 近似沿流线自太平洋延伸至多米格斯山谷地区。结果表明,一个新识别出的断层系统可为输运海水提供路径, 位于Bent Spring和上Wilmington层序之间的层序边界可能控制着海水的垂直运动。提供三个50年的水管理方案 : (1) 水管理实践不变 ; (2) 设置泥浆墙 ; (3) 将陆地水位提高至海平面以上7.6 m。方案3最有效地逆转了海水入侵。测试了水管理方案1和3情境下, 海平面瞬时上升1 m时的影响。两个100年的模拟结果表明, 方案1中海平面上升1 m可能会加速海水入侵, 然而方案3仍然有效地控制了海水入侵。
Resumo
A bombagem de água subterrânea tem levado a grandes rebaixamentos nos níveis de água e a intrusão marinha no litoral de Los Angeles, Califórnia (EUA). Foi implementado um modelo de transporte de solutos baseado no modelo SUTRA para testar as implicações hidráulicas de um modelo de sequência estratigráfica na área de Dominguez Gap e para avaliar os efeitos de diversos cenários de gestão de água. O modelo é bi-dimensional, vertical, e segue uma linha aproximada de fluxo que se estende desde o Oceano Pacífico, atravessando a área de Dominguez Gap. Os resultados indicam que um novo sistema de falhas agora identificado pode fornecer um caminho para o transporte da água marinha, e que um limite estratigráfico situado entre as sequências de Bent Spring e Upper Wilmington pode controlar o movimento vertical da água do mar. Foram considerados três cenários de gestão de água para períodos de 50 anos: (1) sem alterações nas práticas de gestão de água; (2) instalação de uma parede moldada; e (3) elevação dos níveis das águas interiores até 7.6 m acima do nível do mar. O cenário 3 foi o mais eficaz, por conseguir inverter a intrusão marinha. Também se testaram os efeitos de uma subida instantânea de 1 m do nível do mar usando os cenários de gestão de água 1 e 3. Os resultados de duas simulações para 100 anos indicam que uma subida de 1 m do nível do mar pode acelerar a intrusão marinha para o Cenário 1; no entanto, o Cenário 3 mantém-se eficaz no controlo da mesma.
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Acknowledgements
This research was funded by the US Geological Survey’s Cooperative Research Program, the Water Replenishment District of Southern California, and the US Geological Survey’s Coastal and Marine Geology CABRILLO Project. The authors would like to thank the following for contributing to the improvement of the paper: W. Sanford, B. Edwards, P. Renard, C. Gallo, R. Rossetto, and two anonymous reviewers.
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Nishikawa, T., Siade, A.J., Reichard, E.G. et al. Stratigraphic controls on seawater intrusion and implications for groundwater management, Dominguez Gap area of Los Angeles, California, USA. Hydrogeol J 17, 1699–1725 (2009). https://doi.org/10.1007/s10040-009-0481-8
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DOI: https://doi.org/10.1007/s10040-009-0481-8