| Abstract: | The hydrogeological and geochemical characteristics of the hyporheic zone were studied for a year on a 30 m2 site within a stream in the Pyrenees Mountains. This included the drawing of potentiometric maps, measuring hydraulic conductivity and porosity, and the monthly analysis of major chemical elements in water samples. Use of the combined data led to the clarification of certain aspects of the characteristics, functioning and development of the hyporheic zone. Even though the area studied lies in a zone of groundwater recharge, the direct vertical exchange between surface- and groundwater does not seem to be determinant in the potentiometric and chemical development of the area. However, the state of reserves, which can be reduced or reconstituted, seems to play an essential role in flow dynamics, and thus of the chemistry of this area. Flow dynamics in the hyporheic zone apparently are of the longitudinal-transversal type, related to the local stream morphology. The results show how difficult it is to define the hyporheic zone in a structural sense, even though the zone represents an entity that is clearly characterized by specific and identifiable dynamics. |
