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Title: Effects of sediment size on transport capacity of overland flow on steep slopes

Author
item ZHANG, G - Beijing Normal University
item WANG, L - Beijing Normal University
item TANG, K - Beijing Normal University
item LUO, R - Beijing Normal University
item Zhang, Xunchang

Submitted to: Hydrological Sciences Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2011
Publication Date: 10/15/2011
Citation: Zhang, G.H., Wang, L.L., Tang, K.M., Luo, R.T., Zhang, X.J. 2011. Effects of sediment size on transport capacity of overland flow on steep slopes. Hydrological Sciences Journal. 56(7):1289-1299.

Interpretive Summary: Sediment transport capacity, defined as the maximum sediment load that a flow can carry, is a key concept to model soil erosion and sediment transport. Sediment transport capacity is a function of flow hydraulics and sediment size. The effects of sediment size on transport capacity were not well studied on steep slopes, and were the goal of this study. Five sediment size classes (median diameter = 0.10, 0.22, 0.41, 0.69, and 1.16 mm) were used in a laboratory flume in a wide range of flow discharges and slope gradients. Results showed that sediment transport capacity increased as flow discharge and slope gradient increased, and decreased as sediment size increased. Results indicated that sediment size should be explicitly used in estimating sediment transport capacity on steep slopes. The findings should be useful to soil erosion modelers to improve or develop erosion models for steep slopes.

Technical Abstract: Sediment transport capacity is a key concept to determine rates of detachment and deposition in process-based erosion models. Few studies were conducted to evaluate the effects of sediment size on transport capacity of overland flow on steep slopes. The objective of this study was to investigate the effects of sediment size on transport capacity of overland flow in a glued hydraulic flume in a wide range of flow discharge and slope gradient. Unit flow discharge ranged from 0.0007 to 0.005 m square/s, and slope gradient from 8.7 to 42.3%. Five sediment sizes (d50 of 0.10, 0.22, 0.41, 0.69, and 1.16 mm) were used as the test sediment. The results showed that sediment size inversely affected transport capacity. The mean ratios of average transport capacity of the finest sediment (0.10 mm) to those of other sediment sizes were 1.08, 1.24, 1.42, and 1.68 for 0.22, 0.41, 0.69, and 1.16 mm sediment, respectively. Sediment transport capacity of different sediment sizes increased as a power function of flow discharge and slope gradient (r square=0.98), shear stress (r square=0.96), stream power (r square=0.96), or unit stream power (r square=0.86). Transport capacity decreased with sediment size as a power function with an exponent of -0.318. Shear stress and stream power were better hydraulic variables than unit stream power to simulate transport capacity on steep slopes. Sediment transport capacity increased linearly with mean flow velocity. Sediment-inceptive velocity increased as a power function of sediment size (r square=0.98). Further studies with fine soil particles were needed to quantify the effects of sediment size on transport capacity of overland flow on steep slopes.