Tropeano-1984-Earth_Surface_Processes_and_Landforms

256 D. TROPEANO
DATA PROCESSING AND RESULTS
Surveys were made simultaneously at the three sites, between February 1981 and December 1982, following the
rain periods. Plots were sampled, and collected sediments were ovendried and weighed everytime. On the
whole, 140 rainfall events in all sites were identified, together with the relevant runoff and soil loss data. These
numerous data were used in a statistical analysis to make up for the relatively short period of survey. Different
values of cumulative rainfall, peak intensities, total erosive rains and duration of cumulative rainfall were
derived from the rainfall records, and pluviometric parameters were compared with runoff and sediment yield.
The data were processed in the light of four main objectives:
1. To establish the threshold values above which erosion processes start.
2. To determine the range of soil erosion intensities.
3. To estimate the amount of yearly soil loss.
4. To work out empirical formulae for predicting the rate of soil erosion based on given hydrological
characteristics.
The results attained should be reasonably applicable to any areas with physical and environmental
conditions similar to the ones of the plots under survey.
In all three areas it was generally observed that an appreciable amount of sediment yield occurred (of the
order of 5-20 g collected in the troughs) even under the effects of low rainfall intensities (0.07408 mm/min).
However, a more consistent sediment transport took place for slightly higher rainfall intensities, and for
practical purposes the value of 0.12 mm/min was assumed as the lower limit to define rainfall as ‘erosive’.
On the basis of the data collected, two kinds of erosion may be singled out (Table 11): the first one could be
called current erosion and the other mere erosion. The lower limit of rainfall intensity likely to cause severe
erosion may be fixed in all the areas at 0-4 mm/min and the higher peak intensity recorded was around
1.5 mm/min (29 out of the 140 rainfall events recorded lie in this range of erosion). While the average value of
soil loss was very low in the previous range, in this latter condition it rose suddenly to quite considerable values,
with peaks of 1600-1800 g/m and probably more. In Table I11 some of the most significant data relating to
experimental areas are reported, taking into account only the events with peak intensities equal to, or above,
a