Three Decades of Road and Trail Runoff and Erosion 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.

Soil erosion associated with roads—A global review and statistical analysis

“…Depending on the degree of erosion, different types of road‐stream flow paths (i.e., diffused, gullied, and partially gullied) may occur, causing considerable negative effects on local topography, soil, and vegetation. Nevertheless, the off‐site effects stemming from road sediment, especially when it is transported to nearby water bodies, pose a considerable threat to watershed ecosystems (Scharron et al, 2023; Sosa‐Pérez & MacDonald, 2017). Recent studies have delved into the impact of road sediment on river water quality.…”

“…However, other types of unpaved roads may have less confluence capacity than sunken lanes but should not be neglected. bodies, pose a considerable threat to watershed ecosystems (Scharron et al, 2023;Sosa-Pérez & MacDonald, 2017). Recent studies have delved into the impact of road sediment on river water quality.…”

A Review of the Sediment Production and Transport Processes of Forest Road Erosion

“…Firstly, cut slopes consistently experience the most severe erosion intensity and soil degradation in comparison to other road erosion units [40]. Secondly, the sediments deposited on the fill slope mainly originate from the cut slope, road surface, and ditch, resulting in sediment that is predominantly heterogeneous [18]. Moreover, because fill slopes are connected to the lower hillslopes or the riparian zone, they are often considered part of the sediment transport pathways between roads and streams rather than being recognized as focal points for road erosion [18].…”

“…Secondly, the sediments deposited on the fill slope mainly originate from the cut slope, road surface, and ditch, resulting in sediment that is predominantly heterogeneous [18]. Moreover, because fill slopes are connected to the lower hillslopes or the riparian zone, they are often considered part of the sediment transport pathways between roads and streams rather than being recognized as focal points for road erosion [18]. Additionally, as evident in Tables 1 and 2, most existing studies tend to quantify erosion in specific sections or units of the road prism without considering the road erosion units as an integrated whole.…”

“…Within the road prism, studies on road erosion focus on the similarities, differences, and interactions of sediment production processes in different erosion units [18,19]. On a watershed scale, research on forest road erosion examines the alterations in sediment transport efficiency caused by changes in natural water-sediment processes due to road networks [11].…”