Génèse des débits dans les petits bassins versants ruraux en milieu tempéré: 1 - Processus et facteurs

B. Ambroise
1998 Revue des sciences de l eau  
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more » ... ment est protégé par la loi sur le droit d'auteur. L'utilisation des services d'Érudit (y compris la reproduction) est assujettie à sa politique d'utilisation que vous pouvez consulter à l'URI https://apropos.erudit.org/fr/usagers/politique-dutilisation/ Document téléchargé le 13 février 2017 02:12 REVUE DES SCIENCES DE L'EAU, Rev. Sci. Eau 4(1998) 471-495 Genèse des débits dans les petits bassins versants ruraux en milieu tempéré : 1 -Processus et facteurs Streamflow génération within small rural catchments in a temperate environment: 1 -Processes and factors B. AMBROISE Reçu le 8 septembre 1997, accepté le 1 er mai 1998*. SUMMARY This 2-part review on streamflow génération présents the state of the art in both field studies and modelling of the hydrologie behavior of rural catchments. It focuses mainly on temperate environments and water flows within small catchments, but many points hâve a more gênerai signifleance. The first part présents the main results of hillslope hydrology since the 1960s, mainly obtained on small research catchments. It appears that floods can be generated by a large range of both surface and subsurface processes, and not only by infiltration-excess surface runoff, as is still assumed by some hydrologists and modellers. In each case, the processes involved and their combinalions are very variable in time and space, depending on the variable combinations of several environmental factors: précipitation and energy inputs imposed by atmosphère forcings at the upper boundary, variations in initial hydric (soil) and hydrologie (catchment) conditions which cause nonlinearities in catchment responses, water storage and resistance-to-transfer properties of the various compartments (végétation, surface, soil, subsoil) and their interfaces, catchment 3-D topography and morphometry controlling compartment geometry and gravity forces. The non uniform and non random distributions of thèse processes and factors détermine the catchment functional, spatial and temporal organization: (1) at each point, process activation or deactivation results from a balance between water supply from above and local water storage or transfer capacities depending on functional thresholds related to thèse water properties; (2) spatio-temporal variations of factors lead to some récurrence of conditions favorable or unfavorable to each process in some areas of variable extent and some Centre d'Études et de Recherches Éco-Géographiques (CEREG, URA 95 CNRS), Université Louis Pasteur de Strasbourg, 3 rue de l'Argonne, F 67083 Strasbourg cedex. ambroise@geographie.u-strasbg.tr. * Les commentaires seront reçus jusqu'au 31 juillet 1999. 472 Rev. Sci. Eau, 11(4), 1998 B. Ambroise periods of variable duration: this leads to the concepts of "variable active area and/or period" (for a given process); (3) thèse active areas and periods contribuée to outfluxes only if they are hydraulically connectée to the catchment boundaries: this leads to the complementary concepts of "variable contributing area and/or period" (for a given global outflux). Several hydrograph séparation methods are used to estimate various contributions to streamflow, which are difficult to measure in situ. They ail hâve severe limitations: graphical methods are rather arbitrary, tracer methods are based on simplifying assumptions (end-member homogeneity, conservative tracer behaviour...) that are not very realistic. Moreover, considering the same streamflow from différent points of view, they give results that are not comparable but rather complementary: velocity criterion (rapid, delayed, slow flows) for graphical methods, time origin criterion ("pre-event" / "event" water) for water-related isotope tracers, space origin criterion ("source" réservoirs) for other physico-chemical tracers. Lastly, none of them identifies directly the processes involved. Nevertheiess, they are very useful in showing that streamflow is a complex mixing of various water types, with high proportions of subsurface and pre-event water in many cases -contrary to classical hydrologie interprétations. Thus, the complexity and diversity of hydrologie patterns and behaviors observed in small rural catchments, and especially the continuum of streamflow génération situations (from pure surface to pure subsurface contributions), can be analysed and characterized using thèse simple concepts and methods provided by a dynamic Systems approach. They are therefore useful for catchment modelling also (see Part 2).
doi:10.7202/705317ar fatcat:dbi4ygbbjvakfemgfc5yfko4y4