Modelagem da produção de sedimentos em bacia hidrográfica rural sob diferentes equações de eficiência de desagregação do modelo erosivo LISEM
Schlesner, Alexandre Augusto
The Limburg Soil Erosion Model (LISEM) erosion prediction model is an environmental planning and diagnostic tool that, through the simulation of the processes of sediment detachment, transport and deposition provided by runoff, calculates erosion and sediment yield (SY) in watersheds on an event scale. Currently the model presents options for adjusting the detachmentprocess through the use of efficiency coefficients in the form of equations that act as reducers of the detachment level provided by the main disaggregation equation of the model, which obeys the principle of the capacity of transport by the power of the flow adapted by Govers (1990). In simulations for catchments with cohesive soils and rough reliefs, these coefficients may be limiting for the good estimation of SY in erosion modeling. In this work, we tested different efficiency equations by the water flow in a set of 20 events on a small, intensively monitored rural catchment, characterized by shallow and cohesive soils, marked relief and intense agricultural activity. From the three equations tested, one which is used in the EUROSEM model (Morgan et al., 1998) represented by y = 0.79 * exp (-0.85 * COH) satisfactorily simulated SY for 17 of the 20 rainfall-runoff events, compared to the one originally used in the LISEM model that was developed for non-cohesive materials , and also in relation to that used in the MMF model (Morgan et al., 1984), maintaining during the calibration the soil cohesion values measured in the field. For three simulated events the adjustment was not satisfactory due to the particular characteristics of the SY of these events, which do not follow the predictive logic of the erosive process proposed by the model. Thus, the availability of better equations to represent the conditions of the disaggregation for cohesive soils opens up new perspectives for the use of the model in studies of the erosive processes in catchment scale, and the estimation of the SY as a reflection of the conservation management practices adopted in the slopes.