Jean Boiffin

Hydrological structure and erosion damage caused by concentrated flow in cultivated catchments

This study analyses the between-catchment variability of rill volumes produced by concentrated flow erosion during winter in the northern part of the Paris Basin. The working hypotheses were that (i) runoff concentrates along channels determined by topography or by agricultural practices; (ii) rill length is a major component of rill volume variability on a catchment scale; (iii) rill cross-sectional areas are controlled by the size of upslope runoff-contributing areas connected to the corresponding channels. Two samples, one of 20 zero order catchments and the other of 15 catchments, were surveyed. For each catchment, the runoff collector network was modelled from topographical and agricultural information, and split into homogeneous segments. Each segment was characterized by its slope gradient (SL), the soil susceptibility to rill erosion (SSE) and the size of the upslope runoff-contributing areas (RCA) connected to it. These areas were identified by the structural state of their soil surface. The frequency of rill occurrence was highly correlated with RCA and SL. The rill cross-sectional areas of eroded channels were correlated with RCA, SL and SSE. Catchment erosion rates were estimated by adding together the predicted rill volumes for each segment within the catchment. These estimations were closely correlated with observed rill erosion rates. The relative spatial position of runoff collectors must be taken into account when examining the damage caused by concentrated flow erosion.

Rill erosion as a function of the characteristics of cultivated catchments in the north of France

Summary This study analyses variations in rill erosion as a function of the morphological, pedological and land use characteristics of cultivated catchments. 20 elementary catchments in Northern France, from 3.7 to 100 ha, were studied during the winter of 1988/89. The between-catchment differences in total and talweg rill volumes (m 3 ) and rates (m 3 /ha) were very large, and could not be explained by the variations in rainfall. The size of runoff contributing area, defined by combining soil susceptibility to crusting and certain land use characteristics, was found to be the main factor accounting for variations in erosion. Other factors, such as the soil sand content, talweg incisable length, catchment compacity index and proportion of upslope contributing areas were also correlated with total and talweg rill volumes, but slope characteristics were not. Cropping systems greatly affected the catchment susceptibility to rill erosion through their influence on runoff generation, runoff concentration and soil susceptibility to scouring.

Effects of Agricultural Land Use on Spatial and Temporal Distribution of Soil Erosion in Small Catchments: Implications for Modelling

Agricultural land use has important effects on states of the soil surface and on spatial organisation of the catchment, which determines runoff generation and routing. It interacts with geomorphic and climatic conditions to influence the main physical processes involved in soil erosion. Further, it induces great spatial and temporal changes in soil conditions. This paper proposes, in the light of the results of studies that have been carried out in the northern Paris Basin, an approach to take into account these effects and to improve the way to collect input variables for distributed runoff erosion models.