Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986 
669 
Small scale erosion hazard mapping using landsat information 
in the northwest of Argentina 
Jose Manuel Sayago 
San Miguel de Tucumân, Argentina 
raphy with 
scale of 
ABSTRACT : 
a survey 
cond i t i on fluctuât 
A methodology for the erosion hazard 
carry out in an extensive region of 
mapping at s ma Î f 
the no r thwe s t of 
scales is 
Argentine 
described through 
with climatic 
ing from semi arid to wet sub-trop i ca1 . interpretation of mu 1ti-tempora1 
landsat images and conventional aerial photo - i nterpretat i on permit delineation of mapping 
units characterized by the recurrence of landform and land use pattern. Field measurement of 
the USLE factors-rainfall erosivity, soil erodibility, slope steepnes and lenght and coverage- 
potential rates of soil loss following the 
allow to 
criteria 
st ¡mate the erosion hazard expressed 
suggested by S.A. El-Swaify (1977). 
I NTRODUCTI ON 
In developing countries small scale erosion 
maps might be an important tool in order of 
the regional development. They contribute to 
detect areas seriously affected by erosion 
processes where application of conservation 
measures is prioritary. In areas of natural 
vegetation ready to be transform in cultivated 
lands through deforestation they allow to 
stablish the potential risk of degradation. 
Finally, they identify those regions that for 
the complexity of its erosive features and 
the variety of the environmental influences 
must be studied with more detail. 
The region under study, representative of 
the northwest of Argentine for its climatic 
and geomorpho1og i ca 1 conditions, appears 
severely affected by differents erosive 
processes, although there are areas still not 
disturbed. The objectif of this work is to 
carry out an erosion hazard survey in order 
to stablish methodological criteria for the 
mapping of extensive regions at scales rang 
ing between 1:250.000 to 1:1.000.000. 
For the purpose of this work the geomorpho- 
logical units defined by the recurrence of 
internal landscape characteristic represent 
the basic information for the mapping of 
erosion. 
In that sense, the use of satelite info rma_ 
tion assures acceptable planimetric base, a 
multidisciplinary perspective and an object 
ive pursuit of the environmental changes. For 
the evaluation of erosion by water the 
application of parametric criteria contribu 
tes more objectivity particulary through the 
use of methods as for example the Universal 
Soil Loss Equation. 
THE GE0M0RPH0L0G I CAL SECTOR I ZAT I 0N 
Based on the ideas of Verstappen H. Th. (1983) , 
ZonneveId J. I .S. (1983) and Tricart J. (1982) , 
a relief classification for the study areas 
has been established. In this classification 
relief and climate appear as independent 
factors acting as the "substratum" for the 
other landscape factors (soil, vegetation, 
hidrology, fauna, etc.). The classification 
includes five levels of complexity or scale: 
geomorpho1og i ca 1 province, geomorpho1og i ca1 
region, geomorpho1og i ca1 association, geo- 
morphological unit and relief element. Each 
category correspond to a determined scale 
interval that represents a hierarchical leve'l 
of relief sector i zat i on. At each hierarchical 
level, information on landscape factors such 
as for example hydrology, vegetation, soils 
or fauna, with similar levels of complexity 
are to be integrated (Sayago J.M.1982). At 
the scale of this work seven geomorpho1ogica1 
associations, (FIGURE ]) f Q ] lowing partly the 
concepts of Van Zuidam ( 1 9 8 3 ) > wfere character^ 
ized on the basis of the regional meso-climate 
conditions and the geomorpho1ogica1 features 
of major recurrence. 
A1 - Dry-cool mountainous 
terrain 
A2 - Humid subtropical 
steep hilly terrain 
A3 - Humid subtropical 
piedmont plain 
A4 - Dry-wet subtropical 
alluvial plain 
A5 - Dry-wet subtropical 
alluvial overflow plain 
G1 - Arid steep rolling terrain 
G2 - Semi arid sloping terrain 
FIGURE 1 Geomorpho1ogica1 
characterized by 
relief pattern. 
25 Km 
■ 
1 associations 
meso-climate and a typical 
TH F EVALUATION OF EROSION HAZARD 
Erosion hazard can be described as the chance 
that acelerated erosion will start in the 
near future. In cases where accelerated ero 
sion is already in progress the erosion 
hazard would be the degree of further erosion 
that can be expected in the near future. Ero 
sion hazard can decrease when effective