Runoff Generation Processes At Headwater Scale In A Marly Torrential Catchment
Abstract
The study is carried out in a plot of 1330 m2 located on the experimental catchments of Draix (Alpes de Haute Provence, France). Approximately two thirds of the surface are made of a bare marly zone (marls of Callovo-Oxfordien called " Terres Noires "). The upper part is covered by a shrubby vegetation on a soil whose depth does not exceed 70 cm. The plot outlet is equipped with a V-notch weir and a stage recorder. Experiments of chemical and isotopic water tracing have been carried out on this site to (1) provide information about the flow processes (in relation with field observations and hydrometric measurements), (2) to test the relevance of isotope tracers to define at this scale the residence time distribution of new water, (3) to compare the results with those obtained using an hydrological model. For these objectives, a further equipment was added on the plot in spring 2001 : sequential sampler for the collection of discrete rainfall increments (increments of 3 mm), porous ceramic cups for the sampling of soil water and automatic sampler at the outlet. 3 flood events were sampled between the 4th and 25th July 2001. The rainfall amounts were 28.4 mm, 54.2 mm and 29.2 mm producing peak flows of 5.7 l/s, 16.4 l/s and 13.9 l/s, respectively. Despite the physical context (steep slope, impervious material), the discharge coefficients donSt exceed 30 %. This result emphasises the impact of the soil layer (and perhaps the marl itself) on water storage. The storage time and the delay of water transfer are studied using water tracing. Water samples were analysed for major species, dissolved organic carbon and oxygen-18. The first results confirm the important role of the soil on water quality. The chemographs show that a pre-event water contributes to the flow. This impact on water quality may be explained by a rapid movement of water through the subsurface into the soil macropores. The analysis of the input-output relation for isotope concentrations and the application of the EMMA approach using chemical tracers allow to characterise the variation of the hydrological behaviour between 3 successive flood events.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.4559M