Three Decades of Road and Trail Runoff andErosion Work in the Northeastern Caribbean –a Research Program Perspective

Abstract

Highlights The infiltration capacities of unsurfaced roadways are frequently exceeded by rain intensity, promoting overland flow. Erosion rates from unsurfaced roadways and cut slopes are 101 to 104 times greater than on undisturbed hillslopes. Roads in steep, subtropical wet terranes may increase landslide erosion by a factor of 5 relative to areas without roads. The hydro-geomorphic impact of roads is so prominent that they must be explicitly considered in watershed assessments. ABSTRACT. Erosion is a key environmental concern in the northeastern Caribbean because it can diminish soil productivity, damage infrastructure, and threaten human life. Additionally, sediment released by erosion can be delivered to streams where it can degrade water quality and aquatic habitat, reduce reservoir storage capacity, and threaten critical marine resources such as sea grass beds and coral reefs. Road erosion has been a concern in the region since the 1990s, and a considerable body of research has been conducted over the last ~30 years. This article reviews the key findings and identifies additional research needs. In some tropical dry coastal watersheds of the US Virgin Islands and Puerto Rico, unpaved roads and foot or off-road vehicle trails are the primary sediment sources. Watershed scale sediment production rates in these tropical dry settings are 0.3 to 3.7 Mg ha-1 yr-1, depending on unpaved road density, and these are 3 to 40 times greater than under undisturbed conditions. In wetter settings, like the forested and actively cultivated landscapes of highland Puerto Rico, sediment contributions include those from unpaved farm roads but also those from croplands, streambanks, and landslides. Watershed scale sediment production rates in actively cultivated tropical wet settings are 15 to 60 Mg ha-1 yr-1, with road-induced surface erosion and landslides accounting for 50% to 95% of total sediment production. Designing management alternatives will require additional research to improve our understanding of road-to-stream and road-to-coast connectivity, develop effectiveness metrics of applied management practices, and establish the specific causes of road-induced landslides. Keywords: Connectivity, Coral reefs, Landslides, Puerto Rico, Sedimentation, Surface erosion, Virgin Islands.