Correction factor to dye-measured flow velocity under varying water and sediment discharges

SummaryDye-tracing technique was a widely used method to determine the velocity of overland flow in soil erosion studies under both laboratory and field conditions. Few studies were performed to quantify the effects of sediment load on correction factor on steep slopes. This study was conducted to investigate the potential effects of sediment load on correction factor of overland flow to determine mean velocity in a glued hydraulic flume under a wide range of hydraulic conditions and sediment load. Slope gradient (S) varied from 8.7% to 34.2%, unit flow rate (q) from 0.66 to 5.26 × 10−3 m2 s−1, and sediment load (Qs) from 0 to 6.95 kg m−1 s−1. The Reynolds number (Re) ranged from 350 to 5899. Mean velocity was calculated from the volumetric relation using measured flow depth by a digital level probe and flow discharge. The results showed that correction factor decreased as S increased and increased as Re increased for sediment-free flow with a mean value of 0.659. Correction factor could be estimated with a logarithmic function of S and Re (R2 = 0.883). For the sediment-laden flow, correction factor varied from 0.233 to 0.682 with a mean value of 0.466. The correction factor decreased as sediment load (Qs) increased and increased as Re increased. It could be estimated with a logarithmic function of Re, and Qs (R2 = 0.796). For the combination of sediment-free and sediment-laden flows, the correction factor varied from 0.233 to 0.783 with a mean of 0.505. The correction factor was inversely related to slope gradient and sediment load, and directly to Reynolds number (R2 = 0.854). The overall results indicated that caution must be exercised and proper correction be made when using the dye tracer method to measure flow velocity in surface hydrology and erosion studies. Further studies with systematic advanced set up for sediment feeding are needed to quantify the potential effects of sediment load on correction factor under varying conditions of roughness element.