Plot-scale sediment transport processes on a burned hillslope as a function of particle size

Soil moisture, rainfall, runoff, and sediment transport data were collected from four 1-m² hillslope plots after the 2000 Hi Meadow Fire in Colorado. Data were collected daily during three summers, two of which were affected by drought. Maximum 30-minute rainfall intensities, I₃₀, were less than 20 mm h^-1 and the average runoff volumes per plot were less than 4.7 L per storm. The data were separated into three sediment transport processes based on rainfall intensity and runoff magnitude: (1) dry ravel, (2) rainsplash, and (3) rainflow and then into eight different particle size classes (D_i). For each class, dry ravel transport had a non-linear dependence on initial soil moisture, θ_i, with a maximum at intermediate values of θ_i (5-9 % cm³ cm^-3). Dry ravel transport rates were small for low θ_i , which may be caused by a cementation process, and also small for high θ_i , which may be caused by increased surface tension. Rainsplash transport was confined to the I₃₀ domain from 1-7 mm h^-1 was proportional to D_i(I^max₃₀)^0.63. Rainflow transport (I₃₀ > 7 mm h^-1) in shallow flows (h < 2 mm) was most likely dominated by particles rolling. It had a non-linear dependence on D_i with maximum transport of sediment in the 2-4 mm size class. Transport also depended on stream power, but critical stream power was essentially zero, which may indicate that the rainsplash preceding runoff detached soil for transport by overland flow.