Braids :Surface erosion features.May occur in case of strong runoff on mode
rate slopes.The depth is that of a rill hut the width is much greater.
Wide hraids :Occur in case of strong runoff on gentle to moderate slopes.The
width is for example 3-10 meter.
Sheetflood zones :Occur in case of strong runoff on gentle to moderate slopes
In figure 3 the erosion features occurring in the erosion toposequence
are indicated hy a continuous line,crossing the diagram from the lower left
where sheet erosion is indicated on the nearly level summit,and proceeding
upwards to the right.The permanent incisions are indicated in the upper part
where runoff and slope have increased.Gullies may ocqur on more gentle slope
also. To accommodate these gullies, and some others, the diagram would have to
be modified. Figure 3 presents the erosion forms in relation to the volume
of runoff and the steepness of the slop.e.It is of course a generalisation
of the many cases which may occur.lt is clear that the finer distinctions
may only he used in the field.In figure 2 these features are put in between
brackets.
USE OP THE STUDY OP SOIL EROSION TOPOSEQUENCES
The recognition of the presence of a soil erosion toposequence facili
tates the mapping of erosion featuresThe pattern of occurrence will be in
corporated in the map.
The conclusion that there is no soil erosion sequence in an area also
is of importance.The absence of a clear erosion sequence may be due to:
1) land use,field boundaries,conservation measures which interrupt the free
flow of the runoff
2) the relief,the soil and the substratum,one or more of them varying so
much that a regular development of the erosion featurs over the slopes of
the hills is not possible
3) a low erosivity of the rainfall or a very permeable soil and substratum.
Indications about which of the explanations is the most likely may
already be obtained from the AP in many cases. A large field with clear
erosion features may be observed among narrow fields without erosion on the
same siope.Greytone or vegetation patterns may be indicative of a complex
substratum.Large sloping fields of annual crops without signs of erosion
will point to conditions of low runoff(high infiltration,low erosive rain).
The erosion toposequences reflect the tendency of the development of
the erosion.When changes in the land use are considered,like those which
accompany farm improvement,introduction of soil conservation measures,real-
location of land and other development activities,it is of importance to
know the soil erosion hazard and especially that part of the hazard which
depends on relatively permanent factors of climate,relief and soil.This
relatively permanent erosion risk,which can be suitably used in planning,
has been called soil erosion susceptibility.(Bennema et al.1 965 »Brinkman
et al.l973)*The presence of soil erosion partly reflects the erosion sus
ceptibility, in the area.The study of the soil erosion toposequence facili
tates the mapping of the soil erosion susceptibility.
Photo—interpretation along these lines may produce mapping units
which correlate with important differences in runoff conditions.After field
work conservation planning can take the conclusions into account.The three