Modelling Water and Tillage Erosion using Spatially Distributed Models
ABSTRACT Soil erosion models are valuable tools for understanding sedimentary records. In this paper, the potential use of a topography-based
model (WaTEM) for simulating long-term soil erosion and its effect of soil properties is discussed. Long-term (derived from
profile truncation) and medium-term (derived from 137Cs measurements) erosion patterns are compared with simulated patterns of water and tillage erosion. Results showed that WaTEM
is able to describe to reproduce the observed spatial pattern of long-term water erosion reasonably well. However, the 137Cs data indicated that a major change in erosion and sedimentation patterns has occurred over the last decades: the dominance
of water erosion over a time scale of several thousands of years explains the spatial pattern of soil truncation. On the other
hand, the 137Cs data indicate that the present-day pattern of soil erosion is dominated by tillage. WaTEM is also used to assess the effect
of changes in landscape structure on soil erosion. It was shown that, when shifting focus from the field to the catchment
scale, the way we represent space in distributed models affects the model performance at least as dramatically as the physical
description of the process. Finally, a model application whereby WaTEM is linked with a mass-balance model, showed that simulating
the effects of soil erosion on the redistribution of soil properties is an important issue when trying to link surface processes
and sedimentary records.
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ABSTRACT: 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.CATENA. 01/1995;
Article: Measurement and modelling of the effects of initial soil conditions and slope gradient on soil translocation by tillage 1 Paper presented at International Symposium on Tillage Translocation and Tillage Erosion held in conjunction with the 52nd Annual Conference of the Soil and Water Conservation Society, Toronto, Canada. 24–25 July, 1997. 1[Show abstract] [Hide abstract]
ABSTRACT: Tillage erosion studies have mainly focused on the effect of topography and cultivation practices on soil translocation during tillage. However, the possible effect of initial soil conditions on soil displacement and soil erosion during tillage have not been considered. This study aims at investigating the effect of the initial soil conditions on net soil displacement and the associated erosion rates by a given tillage operation of a stony loam soil. Tillage erosion experiments were carried out with a mouldboard plough on a freshly ploughed (pre-tilled) soil and a soil under grass fallow in the Alentejo region (Southern Portugal).The experimental results show that both the downslope displacement of soil material and the rate of increase of the downslope displacement with slope gradient are greater when the soil is initially in a loose condition. This was attributed to: (i) a greater tillage depth on the pre-tilled soil and (ii) a reduced internal cohesion of the pre-tilled soil, allowing clods to roll and/or slide down the plough furrow after being overturned by the mouldboard plough.An analysis of additional available data on soil translocation by mouldboard tillage showed that downslope displacement distances were only significantly related to the slope gradient when tillage is carried out in the downslope direction. When tillage is carried out in the upslope direction, the effect of slope gradient on upslope displacement distances was not significant. This has important implications for the estimation of the tillage transport coefficient, which is a measure for the intensity of tillage erosion, from experimental data. For our experiments, estimated values of the tillage transport coefficient were 70 and 254kgm−1 per tillage operation for grass fallow and pre-tilled conditions, respectively, corresponding to local maximum erosion rates of ca. 8 and 35Mgha−1 per tillage operation and local maximum deposition rates of ca. 33 and 109Mgha−1 per tillage operation.Soil & Tillage Research - SOIL TILL RES. 01/1999; 51(3):303-316.
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ABSTRACT: Soil translocation due to tillage by the ox-drawn ard plough appears to be an important source of colluviation behind stone bunds and lynchets in the Ethiopian highlands. To quantify erosion rates caused by this plough in Ethiopia, painted and numbered rock fragments, 3–5cm in intermediate diameter, were used as tracers to monitor soil movement on 16 sites, each having a different slope gradient, in the district of Dogu’a Tembien, Tigray Region, Ethiopia. Average tillage depth was 8.1cm and the net mean downslope displacement distance per tillage operation ranged from 4.7cm for a 0.03mm−1 slope to 34.4cm for a field with a gradient of 0.48mm−1. There was a strong correlation (R2=0.84, P15cm intermediate diameter) are obstacles to the downslope movement of tilled soil. The unit soil transport rate (Qs) per tillage operation ranged from 4.8kgm−1 on the 0.03mm−1 slope to 38.7kgm−1 on the 0.48mm−1 slope. These values represent the mass of soil deposited by tillage behind 1m of lynchet or stone bund. During each tillage operation the same mass of soil is also removed from the foot of the upper stone bund or lynchet. For the first tillage operation, before the onset of the rainy season, the tillage transport coefficient (K) was 68kgm−1. As farmers till 1–4 times per year, annual K values can be assessed to range from 68 to 272kgm−1. These values are less than those observed for mechanised tillage, which however, is usually conducted on less steep slopes. On average, tillage erosion can be held responsible for half of the sediment deposited behind newly constructed stone bunds in the Tigray highlands.Soil & Tillage Research - SOIL TILL RES. 01/2000; 57(3):115-127.