Road cutslope erosion and control treatments in an actively-cultivated tropical montane setting

Abstract

Although road erosion represents a threat to downstream water resources in many geographical and land use settings, limited evidence exists on the importance of road cutslopes in actively cultivated tropical areas. This study monitored erosion rates from untreated cutslopes and those treated by slope reduction and coir erosion control blankets within the coffee-growing area of western Puerto Rico. Cutslope erosion was inversely related to vegetation cover and averaged 175 Mg ha−1 yr−1, which is up to almost three times greater than unpaved roadbed erosion previously documented for the area. Road density within the study farm is high (44 km km−2) and cutslopes represent almost as much erodible surface area as roadbeds (each ∼14% of the entire actively cultivated farm area). Cutslopes account for 22 – 39% of the 15 – 27 Mg ha−1 yr−1 sediment production rate at the farm scale and induce a net loss of 0.35 ha of potentially cultivable surface area every 25 years. The implemented erosion control practices proved to be very effective and reduced erosion to only ∼3% of untreated conditions. Application of mitigation methods to 13% of the existing cutslopes reduced farm-scale erosion rates to ∼70% of pre-mitigation levels. These findings highlight the need to attend road cutslope erosion in any attempts to reduce the impacts of marginal agricultural lands on soil erosion and water resources in Puerto Rico and elsewhere.