Bed shear stress, surface shape and velocity field near the tips of dam-breaks, tsunami and wave runup: Reply by Peter Nielsen

摘要

A reply is offered to the discussion by Baldock, T E, (2018): Bed shear stress, surface shape and velocity field near the tips of dam-breaks, tsunami and wave runup. Discussion, Coastal Eng, Vol 142, pp 77-81, henceforth B18 of the swash tip model by Nielsen, P (2018): Bed shear stress, surface shape and velocity field near the tips of dam-breaks, tsunami and wave runup. Coastal Engineering, Vol 138, pp 126-131, henceforth N18. The point made by B18, that the near uniform velocity profiles predicted by the N18 model close to the contact point are unrealistic, is substantiated via new data with enhanced vertical resolution due to large bed roughness, K-s approximate to 6.5cm. This data shows that the tip does not actually have a vertical tangent at the contact point. Hence, the main argument for a vertically uniform velocity at a tip, propagating with constant form, falls away. When the N18 model is applied using a measured, non-bullnose, near-tip surface shape it provides realistic velocity profiles and bed shear stress magnitudes. Thus, N18 provides a step towards an integrated explicit 2DV description of swash tips, though not a definitive description.