| Popis: |
Isotopic and chemical studies were carried out from June 1985 to June 1986 on a small agricultural morainic water basin (0,14 km2) to determine the different flow components. The pedologic-lithologic profile is divided into four main horizons: (1) at the surface, a cultural horizon (0–50 cm) clayey and loamy with granular structure; (2) a weathered layer from 50 to 90 cm, also clayey and loamy, but with a compact structure; (3) a fine sandy horizon between 90 and 120 cm; and (4) at the bottom clayey moraine deposits from 120 cm downwards. Measurements were made of precipitation, soil water content, and discharge at the outlet of the basin. Discharges varied between 6 and 53 l s−1 and reflected the snowy-rainy of the basin which received 1036 mm during the twelve-month study. The soil humidity indicates three periods: (1) in summer, a drying period which affects the depth of 90 cm; (2) wetting during autumn which modifies the water content of only the upper 45 cm; and (3) during the winter and spring, saturation of the soil. Tensiometric measurements show a desaturation with upward water movement during the period from September to November. Then a saturation of the whole profile occurs from November to June. This latter period indicates that the 45–80 cm layer acts as a water reservoir. The data monitoring exhibits two systems of flow movement in the soil: (1) a superficial one, which facilitates runoff or subsurface lateral movement, linked directly to precipitation; and (2) a lower system, practically independent from the previous one, originating outside the basin. The water balance in the basin showed an excess of 346 mm over the total of 1036 mm of precipitation. The knowledge of the isotopic gradient of the region suggest a recharge at a mean altitude of 700 m. The water behaviour in the superficial system is directly linked to precipitations the isotopic signal of which moves downwards in the soil. Hydrograph separation of discharge at the outlet indicates the origin of the different flow components. When the runoff flow starts in the river bed after the dry season it is the sandy layer which provides the major flow. Then when the saturation level is reached one can observe lateral |
