Bedform study with the UB-Lab 2C
This research article investigates how the presence of fine sediment (sand and silt) in sand-based riverbeds affects the size and shape of underwater bedforms like dunes and ripples. Using laboratory flume experiments with varying sediment mixtures and flow conditions, the researchers found that non-cohesive fine sediment increases dune height and length, likely due to a phenomenon called the "hiding-exposure effect," which enhances the mobility of coarser sand. Conversely, weakly cohesive fine silt reduces dune size, suggesting decreased sediment mobility. The study also highlights the complex relationship between sediment composition, bedform geometry, and hydraulic roughness, concluding that bedform shape, particularly the leeside angle, is the primary determinant of roughness, not the sediment mix itself. Ultimately, the research aims to improve the prediction of bedform geometry in natural river systems where mixed sediments are common.
Sjoukje de Lange and her collaborators used Ubertone’s acoustic Doppler velocity profiler (ADVP), specifically the UB-Lab 2C model. This device was used to measure flow velocity profiles during the first and last 30 minutes of each experimental run.
The primary interest in using an ADVP in the study was to measure the flow velocity profiles in the flume. This information was then used to estimate hydraulic roughness, a key parameter for understanding how water flows over the bedforms.
The researchers used the ADVP to obtain detailed velocity measurements at different heights above the bed. These measurements allowed them to determine the shear velocity, which is a measure of the frictional force exerted by the water on the bed.
They also used the velocity profiles to calculate the roughness length, which is a measure of the bed's resistance to flow.
Finally, they used the roughness length to calculate Manning's n, a commonly used parameter for quantifying hydraulic roughness.
By using Ubertone’s ADVP, the researchers at Department of Environmental Sciences (Wageningen University & Research, Netherlands) were able to obtain accurate and high-resolution measurements of flow velocity. These measurements were essential for understanding the relationship between bedform geometry and hydraulic roughness.
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