Dye tracing is a common and simple method for measuring surface velocity of overland flow. However, a correction factor is needed to convert the velocity of the dye front to mean velocity. Selecting the appropriate correction factor for particular conditions is complex and its behavior has not been well studied in sheet flow under rainfall on actively eroding surfaces. A series of simulated rainfalls were conducted on a 2 m by 6 m plot with gravelly sandy loam soil. The plot was progressively eroded to examine a wide range of hydraulic conditions. A total of 178 velocities (maximum and mean) were measured using electrolyte and dye tracers over three travel distances (1.65, 3.5, and 5.8 m), and three slope gradients (5%, 12% and 20%). Discharge, sediment yield, random roughness, rock cover, and a range of hydraulic variables were also determined. Mean flow velocity was derived from the centroid of the electrolyte breakthrough curve. Our findings suggest that the velocity correction factor is a dynamic, site specific property. A linear model was proposed to estimate the correction factor based on readily available predictor variables, those being travel distance, unit discharge, and maximum velocity. The results will benefit further investigations of overland flow hydraulics on semiarid rangelands by providing more comprehensive correction factors to determine mean velocity.

染料追踪是一种测量陆上水面速度的常用且简单的方法。但是，需要一个校正因子才能将染料前沿的速度转换为平均速度。为特定条件选择适当的校正因子很复杂，并且在主动侵蚀表面上的降雨条件下的片流中，尚未很好地研究其行为。在一块砂砾壤土上，在2 m x 6 m的土地上进行了一系列模拟降雨。该地块逐渐受到侵蚀，以检查各种水力条件。使用电解质和染料示踪剂在三个行进距离（1.65、3.5和5.8 m）和三个斜率梯度（5％，12％和20％）上总共测量了178个速度（最大和平均值）。还确定了流量，沉积物产量，随机粗糙度，岩石覆盖以及一系列水力变量。平均流速是从电解质穿透曲线的质心得出的。我们的发现表明，速度校正因子是动态的，特定于位置的属性。提出了一个线性模型，以基于容易获得的预测变量（行进距离，单位流量和最大速度）估算校正因子。通过提供更全面的校正系数来确定平均速度，该结果将有助于进一步研究半干旱牧场的陆上水力学。单位排量和最大速度。通过提供更全面的校正系数来确定平均速度，该结果将有助于进一步研究半干旱牧场的陆上水力学。单位排量和最大速度。通过提供更全面的校正系数来确定平均速度，该结果将有助于进一步研究半干旱牧场的陆上水力学。