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MHYDAS - Spatially Distributed Hydrological Modelling of AgroSystems : Model development and application cases for water and pollutant transfer in various agro-hydro-meteorological conditions

Congress: 2008
Author(s): R. Moussa(1), M. Voltz(1), P. Lagacherie(1), P. Andrieux(1), F. Colin(1), C. Dagés(1), J.C. Fabre(1), X. Louchart(1), D. Raclot(1), N. Chahinian(1)(2), B. Tiemeyer(3), J.B. Charlier(1)(4)
Corresponding author : Roger Moussa, INRA, UMR LISAH, 2 Place Viala, 34060 Montpellier Cedex 1, France. Tel : 04 99 61 24 56; Fax : 04 67 63 26 14; email : moussa@supagro.inra.fr (1) Laboratoire d'étude des Interactions entre Sol, Agrosystème et Hydros

Keyword(s): Hydrological modelling, Hydrological processes, Farmed catchments, Water and pollutant transfer;
AbstractIn agricultural catchments, hydrological processes are largely variable in space due to human impact causing hydrological discontinuities such as ditches network, field limits, drains, and tillage practices. MHYDAS, a distributed hydrological model, was especially developed to take into account these hydrological discontinuities. MHYDAS is based on a segmentation of the basin surface into “hydrological units” taking into account hydrological discontinuities, a segmentation of the aquifer into “aquifer units” and a segmentation of the channel network into reaches. Runoff from each hydrological unit is estimated using a deterministic model based on the pounding-time algorithm and then routed through the ditches network using the diffusive wave equation. Detailed descriptions are provided for the main model procedures: subdivision of the catchment into units, computation of rainfall excess, infiltration, baseflow, exchange between channel network and groundwater, and routing flow on hillslopes and through the channel network. A pollutant and erosion transfer module were also developed, and a friendly graphical user interface is under development. Three kinds of parameters can be distinguished : geometrical characteristics of fields and ditches extracted from DEMs, soil hydrodynamic properties measured in-situ and parameters to be calibrated. MHYDAS enables to simulate the part of rainfall infiltrated on hydrological units, the part of flow exchanged between the ditch network and the groundwater and the hydrograph at the fields and the catchment outlets. Application cases for water and pollutant transfer in various agro-hydro-meteorological conditions are presented and compared : i) on a vineyard experimental catchment in Mediterranean climate (Hérault, southern France); ii) on artificially drained lowland catchments in temperate climate (Rostock, northern Germany); iii) on a tropical banana crop catchment on volcanic deposits (Guadeloupe, French Antilles). The model was calibrated and validated at both the plot (1000 – 10000 m²) and the catchment (0.2 – 10 km²) scales. Results show the impacts on water and pollutant transfer of hydrological discontinuities (field limits, tillage practices, ditches, drains), of various climatic conditions (mediterranean, temperate and tropical) and various vegetation cover (vineyard, wheat, banana).
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