Runoff and Soil Erosion Assessment on Forest Roads Using a Small Scale Rainfall Simulator

Julian Zemke

doi:10.3390/hydrology3030025

Abstract

Forestry operations can significantly alter hydrological and erosional processes in a catchment. In the course of developing timberland, a network of persistent roads and skid trails causing soil compaction is usually established. Hereby, the infiltration rate of the soil is distinctly reduced, which leads to the generation of overland flow—this may also cause soil erosion. In this study, a small-scale rainfall simulator is used to investigate hydrological and erosional processes on forest roads and skid trails. The results show increased runoff rates on forest roads, up to 25 times higher than on undisturbed forest topsoil. On skid trails, the runoff rates were altered especially in rutted areas (16 times higher) while unrutted parts showed a lesser change (four times higher). With sufficient overland flow, soil erosion rates also rose, particularly when the vegetation cover of the surface was removed: bare road surfaces featured higher mean erosion rates (195 g·m−2) than partly or completely vegetated skid trails (13 g·m−2) and undisturbed sites (5 g·m−2). The findings presented in this study indicate the need for the use of compaction reducing technology during forestry operations and a revegetation of road surfaces in order to minimize the detrimental factor of roads and skid trails on water retention and soil conservation.

Highlights

Forestry operations usually go along with the construction of a more or less dense forest road network
The findings presented in this study, show a median of 20.02 gm2 on rutted skid trails and 4.64 gm2 on undisturbed sites
As there are only very few studies on this subject in Europe, the objective of this study was to investigate the effects of roads and skid trails on runoff generation, water retention and soil erosion processes in forested catchments

Summary

Introduction

Forestry operations usually go along with the construction of a more or less dense forest road network. These forest roads feature soil properties that differ significantly from adjacent undisturbed topsoil. In the course of establishing a sufficient trafficability, different actions are taken to ensure a stable and durable road surface. The most commonly realized method of forest road construction is a simple grading, which produces a solid surface out of the in-situ soil without the addition of other construction material. If there is a need for a more stable road surface, for instance because of heavy traffic or on steep road segments, an additional fortification is often used. A subgrade made out of chippings or gravel is built to increase the surface stability [1,2,3]

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