EROSIONE E TRASPORTO SOLIDO IN PICCOLI BACINI INTERESSATI DA PIANTAGIONI DI EUCALITTO· SEDIMENT AND EROSION IN SMALL BASINS WITH EUCALYPTUS PLANTATIONS

Some observations were done in three experimental basins and in two plots with different soil use condition, in relation to the vegetation. The first graied basin is covered with herbaceous vegetation; the second and the third one are eucalyptus coppices differently aged. The plots are different thesis in order to the eucalyptus density and grade conditions. The hydrological and erosion data, which are collected from 1990 to 1994, show that the erosion is related with the vegetaI coverture and the coppice density. The runoff in the first basin is higher than the overland flow in the third one. The young coppice show intermediate values ·until the cutting after which they become higher. The torbidity values are always higher in the second wathershed ( 3 aged coppice) than the values in the other basins. During two rainfalls were measured 149.3 g/l in basins with herbaceous vegetation, 219.0 g/l in the coppice with many erosion contributing areas and 137.8 g/l in the third watershed. The plots observations show the different contribute at the basin runoff In the 1st plot (P1), with a low cover density, there are high values than the 2nd plot (P2), with uniform cover condition. The torbidity is higher in P 1 with more than 100 g/l of suspended sediment. In P2 were measured values smaller than 30 g/l. The uncovered areas contribute to the erosion more than the areas with good cover condition.