Multi-criteria assessment of the Representative Elementary Watershed approach on the Donga catchment (Benin) using a downward approach of model complexity

N. Varado (1, 2) , Isabelle Braud (1, 2) , S. Galle (1, 3) , M. Le Lay (1) , L. Séguis (3, 4) , B. Kamagate (4) , C. Depraetere (1)

1 LTHE - Laboratoire d'étude des transferts en hydrologie et environnement
2 CEMAGREF - Centre national du machinisme agricole, du génie rural, des eaux et forêts
3 IRD Benin
4 HSM - Hydrosciences Montpellier

This study is part of the AMMA – African Multidisciplinary Monsoon Analysis – project and aims at a better understanding and modelling of the Donga catchment (580 km², Benin) behaviour. For this purpose, we applied the REW concept proposed by Reggiani et al. (1998, 1999), which allows the description of the main local processes at the sub-watershed scale. Such distributed hydrological models, which represent hydrological processes at various scales, should be evaluated not only on the discharge at the outlet but also on each of the represented processes and in several points of the catchment. This kind of multi-criteria evaluation is of importance in order to assess the global behaviour of the models. We applied such multi-criteria strategy to the Donga catchment (586 km²), in Benin. The work is supported by a strategy of observation, undertaken since 1998 consisting in a network of 20 rain gauges, an automatic meteorological station, 6 discharge stations and 18 wells.

The first goal of this study is to assess the model ability to reproduce the discharge at the outlet, the water table dynamics in several points of the catchment and the vadose zone dynamics at the sub-catchment scale. We tested two spatial discretisations of increasing resolution. To test the internal structure of the model, we looked at its ability to represent also the discharge at intermediary stations. After adjustment of soil parameters, the model is shown to accurately represent discharge down to a drainage area of 100 km², whereas poorer simulation is achieved on smaller catchments. We introduced the spatial variability of rainfall by distributing the daily rainfall over the REW and obtained a very low sensitivity of the model response to this variability. Our results suggest that processes in the unsaturated zone should first be improved, in order to better simulate soil water dynamics and represent perched water tables which were not included in this first modelling study.

Domaines: Interfaces continentales, environnement; Océan, Atmosphère; Sciences de la Terre

N. Varado, Isabelle Braud, S. Galle, M. Le Lay, L. Séguis, et al.. Multi-criteria assessment of the Representative Elementary Watershed approach on the Donga catchment (Benin) using a downward approach of model complexity. Hydrology and Earth System Sciences Discussions, 2005, 2 (6), pp.2349-2391. ⟨10.5194/hess-10-427-2006⟩. ⟨hal-00330791⟩