THE SOIL EROSION TOPOSEQUENCE 
A soil erosion toposequence is a series of erosion features and corres 
ponding deposition features, recognized by type and intensity,, from the 
summit along the slopes down to the drainageway, when this sequence occurs 
repeatedly in a certain area, along (hill) slopes of similar shape and sub 
stratum influence. 
Erosion sequences have been observed in several landscapes (Bergsma 197o)» 
They do not only occur on single hillslopes, but also on complex relief. 
When an erosion sequence occurs one can observe that the erosion types 
and intensities occur in zones more or less along the contour, in strong 
relationship with the relief and the microrelief, as one can analyse it 
according to inclination, shape, and length of slope. On each hillslope the 
same sequence of types and intensities will occur, when the conditions of 
land use and management (crops, tillage, terraces) are comparable. 
The soil erosion sequence is most apparent when there is annual tillage, 
and in agricultural areas of fast natural erosion, A sequence is more often 
observed in agricultural cropland than in grazing areas. In the last case the 
position of the erosion is also determined by the grazing habits of the animals. 
Short sequences do occur, covering only a part of a hillslope, for 
instance the upper slope or the lower slope. This may depend on differences 
in the land use or the substratum. For example, forested parts may give a 
good protection, or permeable parent materials may reduce the erosion to a 
low degree in some parts of the slope. 
The soil erosion sequence results from the development of soil erosion 
in the landscape in the absence of effective soil conservation measures. 
For comparable areas where erosion has not yet progressed very much, the 
erosion sequence may serve as a reference for the erosion which can be 
expect ed,- 
Where an erosion sequence is observed, the erosion features sometimes 
indicate an increase in erosion with the distance from the divide. Local 
wash on nearly level summits, often apparent through reticular greytone 
patterns on the AP change into a linear greytone pattern towards the slope 
where rill erosion becomes dominant. Some way down the slope gullies may be 
observed, shallow at first, lower down becoming deeper. Above the gullies 
sheet erosion may be severe, sometimes decreasing to low intensity between 
the gullies. 
Where an increasing surface erosion with the distance from the divide 
exists, there will be a relation between rainfall and infiltration, resulting 
in Horton overland flow (Horton 1945) or resulting in rapid saturation of a 
shallow upper horizon of the soil profile. 
In the first case the infiltration into the soil is lower than the 
intensity of most of the erosive rains. Accumulation of runoff with 
distance from the divide explains the observed increase in intensity of 
erosion.