Variability of shallow overland flow velocity and soil aggregate transport observed with digital videography

Field experiments at Tiramoana station 30 km north of Christchurch. New Zealand using an erosion plot 16.5 m long 0.6 m wide. and with a slope of 14- 14.5 degrees on rendzina soil aimed to measure the variability of flow velocity and of soil aggregates transport rate in shallow overland flow. Discharge/cross-section area ratio was used to estimate mean velocity, and high-speed digital video camera and image analysis provided information about flow and sediment transport variability. Six flow runs with 0.5-3.0 L s(-1) discharges were supercritical with Froude numbers dose to or more than 1. Mean flow velocity followed Poiseuille law. float numbers were more than 1-5 and hydraulic resistance was an inverse proportional function of the Reynolds number, which is typical for laminar flows. Hence actual velocity varied through time significantly and the power spectrum was of 'red-noise'. which is typical for turbulent flow. Sediment transport rates had even higher variability, and soil aggregates transport was a compound Poisson process. Copyright (C) 2008 John Wiley & Sons, Ltd.