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Ending Groundwater Overdraft in Hydrologic-Economic Systems

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Ending Groundwater Overdraft in Hydrologic-Economic Systems Ending groundwater overdraft in hydrologic-economic systems Julien J. Harou & Jay R. Lund Abstract Groundwater overdraft occurs when extraction Résumé La surexploitation de l’eau souterraine intervient exceeds both natural and induced aquifer recharge over lorsque le prélèvement dépasse la recharge à la fois long periods. While ultimately unsustainable and invari- naturelle et induite de l’aquifère sur de longues périodes. ably having detrimental effects, overdrafting aquifers is Quoique non durable en fin de compte et ayant invaria- common and may be temporarily beneficial within a long- blement des conséquences préjudiciables, surexploiter les term water management strategy. Once a region chooses aquifères est courant et peut être avantageux temporaire- to end overdrafting, water management must change if ment dans une stratégie de gestion de l’eau à long terme. increased water scarcity is to be avoided. Integrated water- Une fois qu’une région choisit de mettre finàla management models allow aquifers and overdraft to be surexploitation, la gestion de l’eau doit changer si une analyzed as part of a regional water-supply system. rareté accrue de l’eau doit être évitée. Les modèles de Incorporating economics into the model establishes a gestion intégrés de l’eau permettent aux aquifères et à la framework for evaluating the costs and effects of surexploitation d’être analysés en tant qu’éléments d’un groundwater management actions on the entire system. système régional d’alimentation en eau. L’incorporation This economic-engineering approach is applied in a case de l’économique dans le modèle établit un cadre pour study of the Tulare Basin in California, USA, where évaluer les coûts et les conséquences des actions de previous economic studies showed optimal pumping gestion de l’eau souterraine sur le système dans son entier. depths have been reached. A hydro-economic optimiza- Cette approche d’ingénierie économique est appliquée à tion model is used to study the economic effects and water une étude de cas du Basin de Tulare en Californie, U.S.A., management actions that accompany ending overdraft. où des études économiques antérieures ont montré que des Results show that when overdraft is prohibited, ground- profondeurs optimales de pompage ont été atteintes. Un water banking using conjunctive-use infrastructure built modèle d’optimisation hydro-économique est utilisé pour between 1990 and 2005 largely annuls the cost of not étudier les conséquences économiques et les actions de overdrafting. The integrated economic-engineering ap- gestion de l’eau qui accompagnent l’arrêt de la sure- proach quantifies effects of groundwater policies on xploitation. Les résultats montrent que lorsque la sure- complex regional water-resource systems and suggests xploitation est interdite, le prélèvement d’eau souterraine promising strategies for reducing the economic costs of mettant en œuvre l’infrastructure pour l’emploi conjoint ending aquifer overexploitation. des eaux superficielles et souterianes construites entre 1990 et 2005, annule dans une large mesure le coût de Received: 7 February 2007 /Accepted: 11 March 2008 l’arrêt de la surexploitation. L’approche intégrée d’ingé- Published online: 29 May 2008 nierie économique quantifie les conséquences des polit- ’ * Springer-Verlag 2008 iques de l eau souterraine sur des systèmes régionaux complexes de ressources en eau et suggère des stratégies Electronic supplementary material The online version of this prometteuses pour la réduction des coûts économiques article (doi:10.1007/s10040-008-0300-7) contains supplementary résultant de l’arrêt de la surexploitation de l’aquifère. material, which is available to authorized users. Resumen La sobre-explotación de aguas subterráneas J. J. Harou ()) ocurre cuando la extracción excede tanto la recarga natural University College London Environment Institute como inducida del acuífero en períodos prolongados. and Department of Civil, Environmental and Geomatic Engineering, Aunque en última instancia es una práctica no sustentable University College London, y que invariablemente tiene efectos perjudiciales, la sobre- Gower Str., London, WC1E 6BT, UK e-mail: [email protected] explotación de acuíferos es frecuente y puede ser temporalmente beneficiosa dentro de una estrategia de J. R. Lund corto plazo de gestión del agua. Cuando en una región se Department of Civil and Environmental Engineering, fi University of California - Davis, decide nalizar con la sobre-explotación, la gestión del Davis, CA 95616, USA recurso debe cambiar a fin de evitar la escasez de agua. e-mail: [email protected] Los modelos de gestión integrada de los recursos hídricos Hydrogeology Journal (2008) 16: 1039–1055 DOI 10.1007/s10040-008-0300-7 1040 permiten analizar los acuíferos y la sobre-explotación como appears as the best way for this region to stop overdraft partes de un sistema regional de abastecimiento de agua. La with the least increase in water-scarcity cost. The model incorporación en el modelo de aspectos económicos shows that conjunctive use infrastructure built between establece el marco para evaluar los costos y efectos sobre 1990 and 2005 would reduce water-scarcity costs to levels el sistema completo de acciones relacionadas con la gestión that existed with overdraft but without the new infrastruc- del agua subterránea. Esta aproximación económica-ingen- ture. The objective of this second part of the paper is to ieril se aplica a un caso de estudio en la Cuenca Tulare demonstrate that groundwater management policies and (California, USA), donde los estudios económicos previos solutions to groundwater problems can be beneficially demuestran que se han alcanzado profundidades óptimas analyzed with integrated hydro-economic models. de bombeo. Se usa un modelo de optimización hidro- económico para estudiar los efectos económicos y las medidas de gestión que se relacionan con la finalización de Overdraft and its consequences la sobre-explotación. Los resultados muestran que cuando se prohíbe la sobre-explotación, el almacenamiento de agua Overdraft exists in many regions and has recently been subterránea usando infraestructura de uso conjunto con- described and labeled differently by several authors. struida entre 1990 y 2005, anula en gran parte el costo de Konikow and Kendy (2005) use the term groundwater no sobre-explotar. La aproximación integrada económica- depletion to describe extraction that causes persistent head ingenieril cuantifica el efecto de políticas hídricas en declines in renewable aquifers or the mining of fossil sistemas regionales de recursos hídricos y sugiere estrate- aquifers. They add that groundwater depletion consists of gias promisorias para reducir los costos económicos de la a reduction of aquifer volume or a reduction in the usable finalización de la sobre-explotación de acuíferos. volume of fresh groundwater within an aquifer. Overdraft is a form of “overexploitation”—a general expression referring Keywords Over-abstraction . Integrated groundwater to any groundwater development that engenders consequen- management . Hydro-economic modeling . Tulare Basin . ces that are negative or perceived as such, and is sometimes USA called “intensive groundwater development” to refer to the often beneficial economics of the early years of overdraft (Custodio 2002; Custodio and Llamas 2003). Correctly Introduction diagnosing an overdraft condition may not be straightfor- ward since transient pumping effects may cause recharge Overdraft is long-term groundwater extraction at unsustain- and discharge of the aquifer to adjust over long periods able rates manifested by steadily decreasing regional (Theis 1940; Bredehoeft et al. 1982; Custodio 2002). groundwater levels over a period long enough to overlook Adverse effects of overdraft can include: uneconomic seasonal and drought effects. This paper concerns ground- pumping conditions, water quality degradation through water overdraft and its cessation. The first three sections induced intrusion of saline or poor quality groundwater, provide a general discussion of groundwater overdraft flow reduction in streams, wetlands and springs, land including negative and beneficial consequences, managed subsidence, interference with pre-existing water uses and and unmanaged ways to end overdraft, and economic water rights and a gradual depletion of groundwater considerations. The objective of this first part of the paper storage (Sophocleous 2003; Zekster et al. 2005). These is to describe overdraft and the drivers behind it within the problems in turn threaten the long-term sustainability of wider context of engineered, economic, and environmental overlying economic activities and society. Land subsi- water resource systems. dence can increase flooding and drainage problems and By choice or necessity, governments or communities disrupt infrastructure such as sewers and aqueducts. By may choose to cease overdrafting groundwater (Custodio lowering the potentiometric surface, overdraft may induce 2002; Blomquist et al. 2004; Kretsinger and Narasimhan intrusion of lower quality waters (seawater, saline ground- 2006). Societies respond to groundwater depletion by water, contaminant plumes, or contaminants in the augmenting, conserving, and reallocating existing supplies sediment or rock matrix) into aquifers, although these (Molle 2003; Konikow and Kendy 2005). However, conditions also can occur in non-overdrafted aquifers. transitioning to sustainable groundwater management with Consistent lowering of the water table can dry up wells,
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