Contributions of runoff from paved farm roads to soil erosion in karst uplands under simulated rainfall conditions

Abstract

In upland areas, paved farm roads (PFRs) change surface hydrological characteristics and may affect soil erosion. The effect of runoff from PFR (hereafter, road runoff) on soil erosion at the road shoulder edge was investigated at two rainfall intensities (50 and 75 mm/h) under laboratory conditions. Two road shoulder edges (i.e., acute angle (AA) and right angle (RA) intersections between the road shoulder and soil surface) were simulated at a 10° slope, and road runoff rates were applied of 0.4 and 0.6 m3/h, which are typical rates for a 2 m wide road under 50 and 75 mm/h rainfall intensity, respectively. A surface without road runoff served as a control (CK). The experiments showed that at the 50 mm/h rainfall intensity, no surface runoff was generated for the CK, while the mean surface runoff was 0.34 and 0.38 m3/h for RA and AA, respectively; at the 75 mm/h rainfall intensity, the mean runoff and sediment yields increased to 9–15 times that of the CK. The road runoff caused rill erosion, shortening the surface runoff initiation time and greatly increasing the sediment loss for AA and RA. Moreover, road shoulder edge patterns impacted soil erosion by influencing the confluence patterns of road runoff, surface runoff and rill development. Because the soil surface is low for AA, it promotes a more concentrated flow along the road shoulder than RA, potentially limiting lateral erosion and downward erosion during rainfall. Indeed, compared to AA, on average, the rill length for RA was 13%-28% shorter, the rill depth and width were 9%-65% greater; and the sediment yield was 26%-64% higher. Therefore, road runoff increases soil loss near the road shoulder, and it is necessary to either divert road runoff away from the shoulder or reduce flow erosivity through appropriate land management.