Correction factor for determining mean velocity of shallow flow on rough surfaces under varying inundation conditions using dye tracer method

Accurate estimation of mean flow velocity is crucial for hydraulics and soil erosion studies. A correction factor (alpha) is required to convert flow surface velocity to mean velocity when using the dye tracer method. However, the determination of an appropriate alpha value is challenging and little information is available about how alpha varies with progressive inundation conditions, especially for rough surfaces with protruding roughness elements (e.g., stones). Therefore, laboratory experiments were conducted in a flume with sandpaper (SD) and stones (ST) surfaces to investigate the impact of roughness elements on the correction factor with varying inundation conditions. The results showed that using a single alpha value is inappropriate for rough surfaces. The correction factor was positively correlated with the Reynolds number and is controlled by flow regimes as well. Moreover, the impacts of inundation conditions as well as protruding roughness elements should be taken into account for determining alpha. Correction factor varied non-monotonically with inundation ratio, depending on the progressive inundation status of protruding roughness elements. The developed equations introducing the inundation ratio performed well in predicting alpha, with R-2 = 0.86 and NSE = 0.91. The results contribute to our understanding of measuring mean flow velocity using the dye tracer method.

Automated summary

Accurate estimation of mean flow velocity is crucial for hydraulics and soil erosion studies. The determination of an appropriate correction factor (alpha) for converting flow surface velocity to mean velocity is challenging, especially for rough surfaces with protruding roughness elements. Laboratory experiments were conducted to investigate the impact of roughness elements on the correction factor under varying inundation conditions. The results showed that using a single alpha value is inappropriate for rough surfaces and the correction factor is influenced by the Reynolds number and flow regimes.