Effect of Forest Road Gradient on Amount of Runoff and Sediment(Case Study: Kohmiyan- Azadshahr Forest)

Roads provide access to forest resources for properly management of timber production, transportation, forest protection and ecotourism. Forest road networks are usually the main source of sediment in forest watersheds. Globally, soil erosion is one of the most important environmental problems which is threaten soil and water resources. Therefore, poor planning and construction causes pollution of forest streams and damage to aquatic life. Road Gradient is one of the main factors of road construction standards. Determining the relation between road gradient and amount of sediment production can be used efficiency by forest manager to choose proper gradient for new roads. This study was conducted in Kohmiyan Forest-Gorgan, and three different segments with 3% 6%, 6%-9% and 9%-12% gradient were selected on road network. investigation Using rainfall simulation the effect of road gradient on amount runoff production and sediment was assessed. In three segments, other parameter such as: roadbed, amount traffic and precipitation are similar. The results indicated that the average amount of runoff produced in segment 1 (gradient 3%- 6%), segment 2 (6%- 9%) and segment 3 (9%-12%) were 21.00, 35.60 and 51.10 litter respectively for each one square meter and average amount of sediment were 3.54, 8.11 and 12.11 g/l. The results of analysis of variance showed significant differences between amount of runoff and sediment due to road gradient. The results of Tukey test showed significant differences among mean runoff and sediment of three segments and increasing with increased road gradient. So keeping the road gradient in standard range is an important factor for controlling runoff and sediment.