The Relations of Rainfall Duration and Intensity and Sediment Yield from Treated Ditch by Conservation Practices in Forest Roads

The side ditch, which is built for the purpose of draining the surface currents and protecting the road construction, is eroded under the influence of the runoff speed during heavy rains and the sediments are transferred to the rivers and water ecosystems. Determining the impact thresholds of rainfall in different protection treatments on the sedimentation process of the side ditch can be a suitable tool for managing and planning the side ditch protection of forest roads throughout the year. The use of environmentally friendly techniques for the protection of roadsides has a direct effect on the quality and durability of road construction and ensuring traffic safety.

In this research, while monitoring the intensity and duration of rainfall of Dr. Bahramnia's forestry project in Golestan province and collecting data throughout the year, in relation to measuring the amount of sediment delivered after each rainfall through trapping at the beginning And the end of 30 plots of 150 meters in the first year before applying the treatments. The trapping involved digging a cylindrical pit with a diameter of 0.4 meters and a depth of 0.6 meters. Inside each trap, a calibrated indicator was installed to repeat the measurements, and during each visit, the sediment height and deposition level were measured to calculate the sediment volume and then multiplied by the apparent specific gravity of the sediment. In the second year, after identifying the streams that had the highest amount of sedimentation, the treatments of rocking with mountain material, rocking with river material, stair-stepping of the stream and pounding of the bed were carried out and the measurement of sediment after each rainfall, the same as the previous year was repeated.

Pearson correlation analysis showed that amount of sediment yield significantly increased by increasing rainfall duration. But, there wasn’t significant correlation between sediment yield and rainfall intensity. The amount of sediment yield decreased with preparing ditch conservation treatments. The sediment production was begun at 12 hours rainfall with intensity of 6.09 mm hr-1. Sediment production from the treatments of rocking with mountain material, rocking with river material, stair-stepping of the stream and pounding of the bed were 16000, 36000, 12150 and 27000 g yr-1.

With comparisons of conservation treatments it was concluded that riprap with mountainous materials had best performance by sediment reduction of 84%. Nevertheless, it is suggested to carry out more and more comprehensive researches under different conditions of climate, slope and bedrock so that generalizable and practical results can be provided to control the sedimentation of the side streams.