particles are transported over a short distance from high to low positions 
in the microrelief of the arable surface.Local accumulation of material may 
occur under tufts of grass for example.The AP may show a reticular greytone 
pattern. 
Rainwash :This type of erosion is dominant in cases of low runoff on gentle 
slopes.Microrilling takes place.(Leopold et al.l964).The combination of 
rainimpact and runoff may have the effect of strong sheet erosion,which may 
show on the AP.The influence of the relief causes a main direction of trans 
port,usually only visible in the field. 
Rills :They occur mostly in case of moderate runoff on moderate slopes.When 
the rills vary in position with time or the season,their effect may be a 
rillwash.Rills are linear,but shallow,erosion forms,less than 30 cm(Bennett 
1955) or 50 cm (Richter I 965 ) deep,and not wider than 50 cm.They can be 
removed by ploughing.They occur singly or in groups.A variation of this 
type of erosion is the ploughrill erosion.Linear greytone texture on medium 
scale AP may result - 
Gullies :They occur in case of strong runoff,often because of lateral concen 
tration of the runoff due to the relief.They may occur on very gentle to 
steep slopes.They can not be obliterated by normal tillage operations.Size 
classes may be defined by depth.For example:shallow gullies (up to one 
meter deep) do not interfere strongly with the communications on the land, 
their stereodepth is not visible on AP of medium scale.Deep gullies(one - 
three meter deep) do not interfere strongly with the communications on the farm, 
stereodepth on medium scale AP is visible.Classes for very deep gullies and 
ravines may be made when necessary. 
Fig.3 Forms of rainwater erosion on the Coto Alto, schematic diagram 
Northern slope under annual crops 
Southern slope under natural vegetation 
) based on Richter. 1965