Effectiveness of water diversion and erosion control structures on skid trails following timber harvesting

- The amounts of soil loss increased with increasing distances between water bars.
- The amounts of runoff and soil loss increased with increasing trail gradients.
- The longest distance on gradients >20% resulted in the highest amounts of erosion.
- The soil erosion was always greater on the silty loam than the clay loam texture.

Sediment in forested watersheds is produced primarily from highly disturbed areas such as skid trails. Forestry best management practices (BMPs) have been developed to minimize erosion and water quality problems, but the efficacies of various BMP options such as water bars are not well documented. The aim of this study was to evaluate the effects of different distances (slope lengths) between water diversion structures (water bars) on runoff volume and soil loss on different skid trail gradients on two soils with different textures. The treatments were located in an Iranian temperate forest and included combinations of three levels of trail gradient (<10%, 10-20% and >20%), four different distances between water bars (25, 50, 75, and 100 m), and two soil textures (clay loam and silt loam). Results showed that runoff volume increased curvilinearly and soil loss linearly with distances between water bars regardless of the soil texture and trail gradient. The greater distances on trail gradients >20% resulted in the highest amounts of runoff and soil loss; shorter distances on trail gradients <10% resulted in the lowest runoff and soil loss amount for the two tested soil textures. On the clay loam soil, 50 and 75 m were the most effective distances between water bars for trail gradients >20 and <20%, respectively. On the silt loam soil, 25 m and 50 m were the most effective distances between water bars for trail gradients >20 and <20%, respectively. The results of our study confirm that slope angle is a primary factor in controlling surface runoff and soil loss on skid trails and that soil texture becomes increasingly important as slope gradients become steeper. Therefore, reducing skid trail slope during construction skid trails is recommended to decrease surface runoff and soil loss in forest operations. Further, BMPs should consider soil texture in addition to slope gradient when recommending spacing between water bars.