Definition
In marine geosciences, the bottom boundary layer (BBL) refers to a layer of flow in the immediate vicinity of the solid sea bottom where the effects of viscosity are significant in determining the characteristics of the flow. The BBL was first discovered by Prandtl (1905) in aerodynamics and subsequently applied to other fluids moving on the surface of a solid body.
Starting upwards from the sea bed, the total thickness of the BBL is defined as the distance above the bottom at which the mean flow velocity equals to 0.99 U ∞, where U ∞ is the free-stream velocity of a layer that is in a geostrophic balance overlying the BBL. On top of the geostrophically balanced layer is a surface layer subjected to wind-wave mixing. When both the bottom micro-topography is uniform and the overlying flow is steady, the BBL can be easily quantified from the vertical flow structure. Various ways exist to estimate the thickness δ of the BBL under neutral conditions (e.g., Grant and Madsen, 1986...
Bibliography
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Prandtl, L., 1905. Verhandlungen des dritten internationalen Mathematiker-Kongresses in Heidelberg 1904, Krazer, A. (ed.), Leipzig: Teubner, p. 484. English trans. Ackroyd, J. A. K., Axcell, B. P., Ruban, A. I. (eds.) 2001. Early Developments of Modern Aerodynamics. Oxford: Butterworth-Heinemann, p. 77.
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Zhang, W. (2014). Bottom Boundary Layer. In: Harff, J., Meschede, M., Petersen, S., Thiede, J. (eds) Encyclopedia of Marine Geosciences. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-6644-0_134-1
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DOI: https://doi.org/10.1007/978-94-007-6644-0_134-1
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