Mesurer l'impact des entités linéaires paysagères sur les dynamiques spatiales du ruissellement : une approche par simulation multi-agents

Abstract

International audience<p>Hydrosedimentary fluxes that run from agricultural plots down to the water streams are currently associated with many social, economic and environmental issues such as diffuse pollution, soil infertility, soil loss, floods, etc. While the genesis of these transfers are well-known at the scale of the agricultural plot, flow dynamics occurring on slopes remain poorly understood. This is especially the case in the small basins located in the north-western part of France, where the landscape mosaic, which includes linear networks (hedges, roads, ditches...), tends to complicate the processes. Analyzing the transfer conditions is important for a further integrated watershed management. Hence, in this paper, we propose to use a multi-agent system as a support decision tool to understand the role of anthropogenic linear networks on runoff pathways. We carried out a so-called bottom-up approach, to measure the effects of the local interactions between each linear element on the global hydrological behavior of the watershed. A first spatial analysis index, characterizing the impact of linear networks in the path of runoff, is constructed here from numerical simulations. The results of this study also tend to demonstrate the relevance of Multi-Agent Systems as diagnostic tools to the hydrosedimentary transfers and processes.</p><p>De nombreux enjeux socio-économiques et environnementaux sont associés aux transferts hydro-sédimentaires qui s’organisent au sein des hydrosystèmes, depuis les parcelles agricoles jusqu’aux cours d’eau&nbsp;: pollution diffuse, diminution de la fertilité des sols, pertes en sol, crues turbides, etc. Si les conditions d’initiation de ces transferts sont bien connues à l’échelle de la parcelle agricole, les dynamiques d’écoulements qui se produisent sur les versants restent mal connues, et ce particulièrement dans les petits hydrosystèmes bocagers du nord-ouest de la France, où la mosaïque paysagère et notamment la présence plus ou moins importante de réseaux linéaires (haies, routes, fossés…) tend à complexifier leur dynamique spatiale. Connaître les conditions de transfert est pourtant nécessaire en vue d’une gestion intégrée des bassins versants. Aussi, cette étude propose d’utiliser la simulation multi-agents comme outils d’aide à la décision pour mieux appréhender le rôle des réseaux linéaires d’origines anthropiques sur le parcours des écoulements de surface. L’approche menée, dite ascendante, permet d’analyser l’importance des interactions locales qui ont lieu entre chaque entité linéaire pour mieux comprendre le comportement hydrologique global d’un bassin versant. Un premier indice d'analyse spatiale, caractérisant l’impact des réseaux linéaires sur le parcours des écoulements de surface, est proposé ici à partir des simulations numériques. Cet article ouvre également une discussion méthodologique en analysant la pertinence des systèmes multi-agents en tant qu’outils de diagnostic et d’aide à la gestion des espaces sensibles aux processus de transferts hydro-sédim...

Assessment of structural sediment connectivity within catchments: insights from graph theory

“…It is well known that the assemblages of links and nodes may evolve in accordance with various external forces (e.g., climate, human practices, tectonics). For instance, agent-based models can be suitable to predict the possible evolution of the structure by considering negative and/or positive feedbacks along the edges (Reulier et al, 2016). This paper seeks to develop an original methodology dedicated to the study of sedimentary cascades under the hypothesis that the influence of connectors and paths on sediment delivery is space-dependent.…”

How might sediment connectivity change in space and time?

“…For instance, anthropogenic infrastructure (e.g., hedges, ditches, roads, and land use) may modify the geometry of the flow network structure and may lead to a differentiation between flow routes and sediment routes. To predict the impacts of such complex interplay, an ABM approach can be applied (Reulier et al, ). An ABM is “a set of autonomous and independent agents in interaction, which coordinate their action in an environment and form an artificial organization” (Feber, ).…”

“…A specific model has been developed under ABM for hedgerow landscapes to model surface flow processes and their interaction with anthropogenic infrastructure: LASCAR model (Reulier et al, , ). With this approach, we assess the structural connectivity of a catchment as the proportion of surface areas that is potentially connected to the outlet.…”

“…For cultivated and grassland patches, infiltration and runoff production rates are applied according to field measurements (Reulier, ; Viel, ). More details on this model can be obtained in Reulier et al ().…”

Response to reviewer 2

“…They lie on the largest number of possible paths within the network. Many indices provided by graph theory have been applied to undirected graphs (for a review, see Rodrigue, 2017). Such indices are the result of a long procedure of research held by geographers to formalize spatial networks and spatial interactions (Pumain and Saint-Julien, 2010).…”