Effects of different width of scouring flumes on runoff and sediment yield of colluvial deposits of collapsing hill

Abstract: Collapsing hill is the typical and serious erosion phenomenon in the red soil area of southern China. The colluvial deposit erosion is the main sediment source of collapsing hill, which has the characteristics of loose texture, bad structure, and high erodibility. Study of the influence of elements on erosion sediment in the process of slope erosion is of great significance for revealing the mechanism of slope erosion. The width of scouring flumes is one of the factors that affect the characteristics of erosion and yield of runoff and sediment in the process of slope scouring erosion but now has fewer research achievements. With the colluvial deposits of collapsing hill as the research object, and through the simulated scouring in laboratory, this study intended to disclose the impacts of different width of scouring flumes (10, 20, 30, 40 and 50 cm) and discharge per unit width (1.2×10-2, 2.4×10-2, 3.6×10-2 and 4.8×10-2 m2/min) on the slope scouring erosion and runoff and sediment yield of colluvial deposits. Soil samples were collected from the Longmen Town, Anxi County, Fujian Province in southeast China, and preprocessed according to the experimental standards. Results showed that: 1) The width of scouring flumes had significant effects on the runoff rate and sediment yield rate when the discharge per unit width was 1.2×10-2, 2.4×10-2 and 3.6×10-2 m2/min (P<0.05), while had no significant effects when the discharge per unit width was 4.8×10-2 m2/min; 2) When the discharge per unit width was 1.2×10-2 m2/min, the runoff rate increased gradually with the increase in time, when the discharge per unit width was 2.4×10-2 and 3.6×10-2 m2/min, the runoff rate increased at first and then became stable with the increase in time, and when the discharge per unit width was 4.8×10-2 m2/min, the runoff rate increased at first and then decreased with the increase in time; when the discharge per unit width was 1.2×10-2 m2/min, the trends of sediment yield rate and sediment concentration over time under different width of scouring flumes were different, and when the width of scouring flumes was 10, 20 and 30 cm, the sediment yield rate and sediment concentration increased at first and then became fluctuant, but increased with time all the way while the width of scouring flumes was 40 and 50 cm; when the discharge per unit width was 2.4×10-2, 3.6×10-2 and 4.8×10-2 m2/min, the sediment yield rate and sediment concentration under each width of scouring flumes showed an increase-stability-decrease trend with the increase in time; 3) When the discharge per unit width was constant, the difference of the cumulative runoff yield under different width of scouring flumes was not significant, and that of the cumulative sediment yield and the average sediment concentration were significant (P<0.05) while the discharge per unit width was 1.2×10-2, 2.4×10-2 and 3.6×10-2 m2/min; when the discharge per unit width was 4.8×10-2 m2/min, the width of scouring flumes had no significant effects on the cumulative sediment yield and the average sediment concentration; 4) The width of scouring flumes had no effects on slope erosion and characteristics of runoff and sediment yield when the discharge per unit width was 4.8×10-2 m2/min, and thus, faculative width of scouring flumes could be chosen while the discharge per unit width was 4.8×10-2 m2/min. This research has used the colluvial deposits of collapsing hill as the research object and carried out the experiments under the condition of 15° slope, but colluvial deposits' characteristics (loose texture, bad structure, high erodibility) are obviously different from other soil types, and thus, more studies aiming at other soil types about the effects of different width of scouring flumes on erosion and yield of runoff and sediment are needed, and further researches can also be conducted with other slope gradients.