Effects of Pinus tabulaeformis litter cover on the sediment transport capacity of overland flow

Sediment transport capacity (Tc) plays a pivotal role in process-based soil erosion models. Surface cover is an important factor that affects Tc; investigation into the potential effect of litter cover on Tc is limited. The objectives of this study were to quantify the effects of Pinus tabulaeformis litter cover on Tc; to explore various relationships between hydraulic variables, litter cover, and Tc; and to compare the similarities and differences of the effect of litter and stem cover on Tc. Experiments were conducted in a 5 x 0.38 m flume. The unit flow discharge varied from 1.316 x 10(-3) to 3.947 x 10(-3) m(2) s(-1), and the slope gradient varied from 8.8 to 26.8 %. Pine needles of Pinus tabulaeformis were selected to simulate litter cover. Seven levels of litter cover were considered: 0%, 5%, 10 %, 20 %, 30 %, 50 %, and 70 %. The median diameter of the test sediment was 0.35 mm. The results showed that Tc decreased exponentially as litter cover increased. Measured Tc could be predicted adequately (R-2 = 0.96) by unit flow discharge, slope gradient and litter cover, or the stream power and litter cover. Flow velocity or unit stream power could predict the Tc equally well (R-2 = 0.95) without including the cover term because the effect of litter cover on the Tc manifests itself in the increased resistance and reduced flow velocity. Tc is most sensitive to the slope gradient when the level of cover is low. The effect of litter cover on Tc could be greater than the unit flow discharge and slope gradient in relative terms when the level of cover exceeded 38 % and 81 %, respectively. The effect of stem cover on Tc is greater than that of litter cover, other variables being the same.