Abstract
The flow rate to fully screened, partially penetrating wells in an unconfined aquifer is numerically simulated using MODFLOW 2000, taking into account the flow from the seepage face and decrease in saturated thickness of the aquifer towards the well. A simple three-step method is developed to find the top of the seepage face and hence the seepage-face length. The method is verified by comparing it with the results of previous predictive methods. The results show that the component of flow through the seepage face can supply a major portion of the total pumping rate. Variations in flow rate as a function of the penetration degree, elevation of the water level in the well and the distance to the far constant head boundary are investigated and expressed in terms of dimensionless curves and equations. These curves and equations can be used to design the degree of penetration for which the allowable steady pumping rate is attained for a given elevation of water level in the well. The designed degree of penetration or flow rate will assure the sustainability of the aquifer storage, and can be used as a management criterion for issuing drilling well permits by groundwater protection authorities.
Résumé
Le flux entrant dans un puits entièrement crépiné recoupant partiellement un aquifère libre est simulé en utilisant MODFLOW 2000 prenant en compte le débit de suintement et décroissance de l’épaisseur saturée dans la direction du puits. Une méthode simple en trois étapes est développée pour trouver le sommet de la zone de suintement et de là, sa hauteur. La méthode est vérifiée par comparaison avec des méthodes prédictives existantes. Les résultats montrent que la composante du flux à travers la surface de suintement peut fournir une fraction majeure du débit total pompé. Les variations du flux en fonction de la profondeur de fonçage, de la cote de l’eau dans le puits et de la limite à potentiel constant lointain, sont étudiées et exprimées en termes de courbes sans dimension et équations. Ces courbes et équations peuvent être utilisées pour déterminer la profondeur de fonçage pour laquelle le débit constant admissible est atteint pour une cote donnée de l’eau dans le puits. La profondeur de fonçage ou le flux déterminés assureront un débit d’exploitation entretenu, et peuvent être utilisés comme critère de gestion pour la délivrance de permis de fonçage de puits par des autorités de protection de l’aquifère.
Resumen
Se utilizó MODFLOW 2000 para simular numéricamente el caudal de pozos parcialmente penetrantes y totalmente provistos de filtros en un acuífero no confinado tomando en consideración el flujo de la superficie de filtración y la disminución en el espesor saturado del acuífero hacia el pozo. Se desarrolló un método simple de tres etapas para encontrar la parte superior de la superficie de filtración y su longitud. El método se verificó por comparación con los resultados de métodos predictivos previos. Los resultados muestran que la componente de flujo a través de la superficie de filtración puede abastecer a una parte importante de la tasa de bombeo total. Se investigaron las variaciones en el caudal en función del grado de penetración, elevación del nivel de agua en el pozo y la distancia hasta el límite lejano de carga constante y se expresaron en términos de curvas y ecuaciones adimensionales. Estas curvas y ecuaciones pueden ser usadas para diseñar el grado de penetración al cual se alcanzó el ritmo de caudal constante de bombeo para una determinada elevación del nivel del agua en el pozo. Este grado diseñado de penetración o caudal asegura la sustentabilidad del almacenamiento del acuífero, y puede ser usado como criterio de manejo para la expedir permisos de perforación de pozos por las autoridades de protecciónde las aguas subterráneas.
Resumo
O caudal para poços parcialmente penetrantes em aquífero livre é simulado numericamente usando o MODFLOW 2000, tendo em conta a zona de drenância e a diminuição da espessura saturada do aquífero em direcção ao poço. Um método simples, de três passos, é desenvolvido para determinar o topo da zona de drenância e, consequentemente, a extensão da mesma. O método é validado por comparação com os resultados prévios dos métodos preditivos. Os resultados mostram que a componente de fluxo através da zona de drenância pode fornecer uma grande porção do total do caudal de bombeamento. Variações no caudal como função do grau de penetração do poço, da posição do nível de água no poço e da distância à fronteira de potencial constante são investigadas e expressas através de curvas adimensionais e equações. Estas curvas e equações podem ser usadas para definir o grau de penetração do poço para o qual a taxa de bombeamento constante admissível é atingida, para uma determinada posição do nível de água no poço. O grau de penetração projectado ou a variação de caudal vão garantir a sustentabilidade do armazenamento do aquífero, e pode ser utilizado, pelas autoridades de protecção das águas subterrâneas, como critério de gestão na emissão de licenças de construção de poços.
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Acknowledgements
The financial support of Fars Regional Water Organization, contract No. 10/101/19199, is acknowledged. The authors appreciate constructive comments and suggestions provided by the Editor and Associate Editor, and by Dr. Zhang Wen and another (anonymous) reviewer. This research was completed when the second author was on sabbatical leave at the University of Waterloo, Canada.
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Behrooz-Koohenjani, S., Samani, N. & Kompani-Zare, M. Steady flow rate to a partially penetrating well with seepage face in an unconfined aquifer. Hydrogeol J 19, 811–821 (2011). https://doi.org/10.1007/s10040-011-0717-2
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DOI: https://doi.org/10.1007/s10040-011-0717-2