Runoff and sediment concentration of different parts of a road in Hyrcanian forests

Abstract

Road prisms, such as cutslopes, fillslopes and road surfaces, can be important contributors of sediment to streams in forested watersheds. In this study rainfall simulations were carried out on cutslopes, fillslopes, road surfaces and forest grounds in hardwood forests of Lolet and Lat Talar, Iran. Water at intensity of 32.4 mm·h⁻¹ was sprayed from a nozzle onto a square area of 0.48 m². Runoff was collected by water gauge every 4 min and then runoff and sediment parameters were measured in each plot. Results indicated that on road surfaces, the runoff coefficient was 63.28%. On the cutslopes and fillslopes, the runoff coefficients were 35.14% and 10.23%, respectively. On the forest ground as a control, the runoff coefficient was 5.90%. Runoff volume was 2.73 mL·s⁻¹ on the road surfaces and 1.52 mL·s⁻¹ on cutslopes. On fillslopes the runoff volume was 0.44 mL·s⁻¹ and on the forest ground 0.25 mL·s⁻¹. The greatest rate of soil loss was found on the cutslope (280.79 g·m⁻²·h⁻¹). The total soil loss from the cutslopes was two times higher than that from the road surfaces and six times higher than that from the fillslopes. We conclude that cutslopes can be considered the main source of sediments in our study sites, but the function of road surface as a source of runoff generation is more important.