1. Introduction

Accelerated erosion may take place following road construction on forested lands. Some possible causes include (a) removal or reduction of protective cover; (b) destruction or impairment of natural soil structure and fertility; (c) increased slope gradients created by construction of cut and fill slopes; (d) decreased infiltration rates on parts of the road; (e) interception of subsurface flow by the road art slope; (f) decreased shear strength, increased shear stress, or both, on cut and fill slopes, and (g) concentration of generated and intercepted water.

Numerous reports substantiate the fact that road construction can accelerate erosion on forested lands (references 1, 2, 4, 6, 9, 14, 15, 18, 19, 20, 22, 24). Experience by FA0 in developing countries has often shown that roads are the major source of erosion. As might be expected, effects vary considerably depending on the geologic, climatic, landform, soil, and vegetation properties of the area or country in question and upon the care taken to reduce erosion in all phases of the road development project. Roads constructed on glaciated, metamorphic parent materials in Colorado, for example, exhibited slight accelerated on-site erosion, but no significant increases in sediment fields were detected downstream (reference 14). In contrast, construction of low standard, temporary logging roads on high erosion hazard granitic slopes in Idaho greatly accelerated on-site surface and mass erosion, causing downstream sediment yields to increase an average of over 45 times (from 8.8 to 396 metric tons per square kilometer per year) for a 6-par study period (reference 19).

The impacts of road erosion are many. The most direct is to the road itself; excessive erosion can, and often does inhibit road use or even make the road impassable until restored, often at great expense. Less obvious, but often more important is the movement of eroded material off the site. This can cause sedimentation which may create excessive damage to downstream cultural and ecological values.

< Back to Reducing Erosional Impacts of Roads

Last Modified: 07/05/2007