Modelo conceptual del sistema acuífero de Enchereda (La Gomera, Islas Canarias): contribuciones a otras islas volcánicas

Hydrogeological conceptual models are difficult to develop in volcanic islands due to scarce hydrogeologic information in the inner parts of the islands and the complex structure of volcanic materials. This complexity is increased by 1) destruction processes (for example, flank collapse) and 2) dike intrusion. Dikes can both channel groundwater flow parallel to their general trend or act as barriers impounding it. In this paper we evaluate the role of dikes and volcanoclastic deposits in Enchereda aquifer system (La Gomera, Canary Islands) regional flow and particularly, in its higher area. In this aquifer system three hydrostratigraphic units can be identified: the Lower Old Basalts, with low permeability; the Volcanic Breccia, impermeable; and the Upper Old Basalts, permeable. The breccia seems to act as the impermeable limit of the aquifer and the reconstruction of its geometry shows a coherent surface dipping about 13o towards the ESE what determines the regional flow in the aquifer. After dike mapping using aerial photograph and orthophotograph as well as mapping in the field and inside Ipalán water tunnel, four dike swarms have been identified. NW-SE dikes are the most frequent ones, and show a maximum density of more than 10 dikes/100 m, similar to rift zones in volcanic islands. These dikes are parallel to the regional flow and channel water flow whereas the N-S and NE-SW swarms impound groundwater rising the water table level forming a stepped surface as they are perpendicular to the regional flow. Lastly, W-E dikes do not seem to have any significant influence on the aquifer. Our results show the need of a re-evaluation of the role of dikes in the regional flow in other volcanic island aquifers in which their influence have been minimized as overlapping of different dike swarms can condition regional flow in the aquifer. La elaboración de modelos conceptuales en acuíferos de islas volcánicas presenta una elevada dificultad debido a la complejidad estructural de los materiales volcánicos, incrementada por 1) los procesos de destrucción (p. ej., deslizamientos de flanco) y 2) la intrusión de diques, que pueden actuar como zonas de flujo preferente o sobreelevando el agua localmente. En algunos casos, la falta de información hidrogeológica en el interior de las islas dificulta aún más la caracterización del funcionamiento de los acuíferos en estas zonas. En este trabajo se evalúa el papel de los diques y de los depósitos volcanoclásticos en el flujo regional de la zona de Enchereda (La Gomera, Islas Canarias) y en particular, en su zona más elevad