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THE ROLE OF UNPAVED ROADS IN THE SEDIMENT BUDGET OF A SEMI-ARID MESOSCALE CATCHMENT

High rates of erosion and runoff production on road infrastructure have
been documented, indicating that unpaved roads might be significant
sources of sediment in catchments. In this paper, the production of
surface sediments from unpaved rural roads at different scales is
assessed. The study took place in northeastern Brazil, in a semiarid
area of the Caatinga biome, vulnerable to desertification. Sediment
production data from road surface segments were monitored for two years
(2013-2014) under conditions of natural precipitation. By using
hydrosedimentological modeling and Geographic Information System (GIS),
the sediment budget was calculated at the meso-scale basin (aprox. 930
km²), in order to identify the relative contribution of roads to the
sediment balance. Universal Soil Loss Equation (USLE) associated with
Maner’s sediment delivery ratio (SDR) equation, proved to be an adequate
approach for predicting sediment yield on the road segment scale; the
best results were obtained for the road without traffic, due to the
non-interference in this segment of external factors, such as traffic
and maintenance activities, not explicitly considered in the model
formulation. The modeling procedure showed that the roads, which occupy
only 0.7% of the catchment surface, were responsible for approximately
7% of soil loss in the area. Furthermore, sediment connectivity might
be enhanced by roads, which cross the river network and, therefore,
deliver more directly the sediment generated at hillslopes. This is
particularly important in the studied environment, where sediment
connectivity is low due to limited runoff and the existence of a dense
network of surface water reservoir