Surface erosion occurs when detachable soils on sufficiently steep slopes are exposed to overland flow and/or the impact of rainfall. Sediments introduced to streams from surface erosion processes are generally fine grained and can influence water quality and aquatic habitat.

Gravity and overland flow of water are natural transport mechanisms of the detached soil particles. Overland flow rarely occurs under natural forest conditions because an absorbent, protective layer of organic material protects the soil. However, any activity that strips this protective layer to the bare mineral surface contributes towards surface erosion. Soil compaction, which diminishes the capability of the soil to quickly absorb free water, leads to readily channeled overland flow and serious erosion consequences. Needless to say, the destructive activities most likely to cause surface erosion are associated with logging practices. Among them are roads, high intensity burns or mechanical scarification, silvicultural practices, poor yarding practices, and natural processes such as wildfire.

The purpose of designing the Surface Erosion Module is to develop information necessary to address key questions critical to understanding erosion processes in watershed context. Two types of erosion processes are addressed in the module, with critical questions for each source:

• Proximity of erosion to the stream system
• Slope angle
• Soil texture, reflecting differences in distances various particle sizes will travel
• Areas where overland flow is likely to occur

• Amount and condition of road prism area that drains directly into the stream system
• Traffic levels on the direct entry area of the road surface and
• Material used for road surfacing.

Some natural conditions that limit delivery of eroded soil to the stream include vegetated areas along streams that can filter out soil particles, and topographic conditions that prevent eroded material from entering the stream. Management techniques may help control the entry of erosion material into streams by minimizing road surface area that delivers directly into the stream, maintaining the road according to traffic levels, and limiting traffic during wet weather.

Introduction

Methods

Results and Discussion

Conclusion

References

Appendix: AML files