The role of hydrodynamic impact force in subaerial boulder transport by tsunami—Experimental evidence and revision of boulder transport equation

The hydrodynamic impact contributes to the initiation of subaerial boulder transport by tsunamis and tsunami-like flows. Here, we consider two approaches to modelling this impact force—hydrostatic and hydrodynamic—and assess the suitability of each in boulder transport models. The model proposed, solved as an ordinary differential equation, eliminates the need to assume a conservative value of flow acceleration. Introducing the hydrodynamic impact force reduces, by almost 45%, the recognised overestimation of threshold flow velocity in simple hydrodynamic models for boulder transport. By contrast, including the hydrostatic impact force reduces the overestimation by less than 10%. We found the new model consistent with the results of simple flume experiments. In these experiments, three rectangular limestone blocks of 27–70 cm³ in subaerial pre-transport setting condition were subjected to tsunami-like flow by sudden opening of a sluice gate.