Sediment transport capacity as affected by different combinations of vegetation litter and stem cover

Abstract

The combined cover of different vegetation types significantly changes hydraulic properties, thereby controlling soil erosion. However, there are still gaps in the research on how sediment transport capacity is affected by combinations of litter and stem cover. Therefore, this study aimed to reveal the hydrodynamic mechanism through which combined litter and stem cover affected the sediment transport capacity and to develop prediction equations of sediment transport capacity under the condition of combined vegetation cover. Locust leaves and wooden cylinders (diameter of 1 cm) were used to simulate litter and shrub stems, with a combination of different coverage levels. The ranges of litter cover and stem cover were 0–70% and 0–30%, respectively. One discharge rate (1 × 10−3 m3 s−1) and one slope gradient (26.8%) were chosen to perform the flume experiments. The results showed that for the same vegetation coverage, the stems in the combined cover had a greater impact on hydraulic parameters and sediment transport capacity than did the litter. The decay coefficient of stem cover to reduce the normalized flow velocity and normalized sediment transport capacity was 2.0 and 2.5 times that of litter cover, respectively. Under the condition of combined litter and stem cover, stem cover affected the relationships between the sediment transport capacity and hydraulic parameters related to flow velocity. When stream power was used to estimate the sediment transport capacity, the stem and litter cover must be used together as additional parameters to improve the prediction accuracy. Flow velocity and unit stream power were the most practical parameters for predicting the sediment transport capacity under the combined cover of litter and stems, with determination coefficients of 0.95.