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Les mutations paysagères du bocage au cours des soixante-dix dernières années (agrandissement des parcelles, suppression des haies et des talus, etc.) tendent à amplifier les transferts d’eau et de sédiments issus du ruissellement sur les parcelles agricoles. Ces transferts peuvent alors générer de multiples aléas : inondation, pollution de l’eau, érosion des sols… En permettant une analyse des interactions qui lient les objets géographiques de différentes natures (haies, parcelles cultivées, mares, chemins, etc.) à l’échelle d’un territoire, l’analyse spatiale et ses outils de modélisation facilitent la mise en place de plans de gestion adaptése du bocage.

Land use and landscape structure play an important role in the functioning of flash floods on the arable plateaus of northern France. Landscape structures have changed considerably over the last decades with an increase in runoff-producing surfaces and an enlargement of the plots. This evolution results in an increase in runoff volumes accompanied by an increasingly easy diffusion of runoff on the slopes. There is therefore potentially an increasingly frequent and important spatial connectivity from the plots to the thalwegs, which can lead to the formation of flash floods. This study proposes to model this diachronic evolution of connectivity in a small agricultural basin of Seine Maritime using a multiagent system (MAS) and to develop synthetic indicators characterising these spatial links in the flow processes. The model outputs show that spatial connectivity has been steadily increasing over the past 70 years due to the enlargement of the parcel grid and the growth of runoff surfaces. For example, for the same 20 mm/h rainfall, the connectivity indicator increases from 40.99% (in 1947) to 78.33% (in 2015). This observation is observed for all levels of rainfall intensity, including the lowest. This modelling, carried out for a 116 ha basin in arable farming, can be transposed to all small agricultural basins. [ABSTRACT FROM AUTHOR]

Abstract Agricultural activity evolution during the second half 20th century has profoundly changed agricultural landscapes in western Europe. Numerous scientific studies have shown that the consequences on erosive runoff processes are important. This study aims show one of the important consequences of these transformations that is the structural connectivity between cultivated plots and the river. The study is based on the analysis of aerial images taken at four different dates (1947, 1967, 1988 and 2014) and on the use of the LASCAR (LAndscape StruCture And Runoff) multi-agent model. It shows how agricultural landscapes have evolved over the past 70 years and how this has altered the connectivity of cultivated plots to the river. In addition to the development of spatial analysis indices, the results of this study offer key understandings relevant to all spatial scales (global to local). The study was carried out on a small agricultural watershed in the northwest of France (Lingèvres, 17.6 km2), whose recent landscape evolution is part of the overall dynamics of northwest French agricultural landscapes transformation. Highlights • Multi-agent simulation is a relevant approach for assessing hydrological connectivity. • Percentage of cultivated areas that are connected to river has more than tripled in 70 years. • Landscape entities organisation in space plays a key role in this hydrological connectivity. [ABSTRACT FROM AUTHOR]

Abstract: Many authors focus on the concept of sediment connectivity to predict the sedimentary signal delivered at catchment outlets. In this framework, the sedimentary signal is seen as an emergent aggregation of local links and interactions. The challenge is then to open black boxes that remain within a sediment cascade, which requires both accurate geomorphic investigations in the field (reconstruction of sequences of geomorphic evolution and description of sediment routes) and the development of tools dedicated to the modeling of sediment cascades. On the basis of study cases in various environmental regimes (high‐energy mountainous environment and agricultural lowland catchments), in this paper, we (a) exhibit some spatial and temporal paradoxes in terms of sediment delivery and (b) develop various modeling procedures to test some hypothesis of interpretations. These modeling approaches explore different components of sediment connectivity at the catchment scale, including graph theory, agent‐based modeling, and differential equations. Each protocol is chosen according to the scientific objective and how the geomorphological system is simplified. Collectively, the results show that connectivity is an efficient conceptual framework with which to predict how a sediment cascade may transmit (or not) a perturbation throughout the system, including local perturbations (local sediment input, removal of a reservoir, etc.) and perturbations due to external‐boundary forces. [ABSTRACT FROM AUTHOR]