Tropical regions have extensive networks of unpaved roads which can be the largest contributor of sediment loading within a watershed in terms of both sediment generation and delivery. A number of erosion and sediment prediction models have been developed for unpaved roads and applied across a wide range of locations. However, little work has been devoted to the comparison of these models or to their application in tropical environments.

A 13 square kilometer mixed land use watershed in Eastern Brazil was used as a case study area for model application and comparison. Models chosen for evaluation were WEPP: Road, SEDMODL, and STJ-EROS. To determine the applicability of these models to the case study watershed, a classification system was developed to score road segments according to sediment production and delivery potential. Field observations provided data for the input parameters of the models as well as to identify which road segments appear to be high contributors of sediment within the watershed. These road segments were compared with the segments estimated by the models to have high sediment yields. The models identified less than 50% of those roads categorized by field observation as having high erosion potential. WEPP: Road matched more closely to the field observations than SEDMODL and STJ-EROS. To be useful tools for watershed management in the tropics, a unified method for calculating sediment delivery is needed as well as an adjustment to model input parameters so that they better reflect conditions in tropical watersheds.