Paleotsunami Inundation of a Beach Ridge Plain: Cobble Ridge Overtopping and Interridge Valley Flooding in Seaside, Oregon, USA

Table 3

Reported equations for calculating flow tractive forces from bed shear stress and critical entrainment shear stress.

Sources	Bottom shear stress
Modified DuBoys	𝑇𝑐=𝜌𝑔𝑑𝑆
Shields^∗ Miller et al. [23]	𝑇𝑐=0.045(𝜌𝑠−𝜌)𝑔𝐷𝑚
Komar [24, 25]	𝑇𝑐=0.045(𝜌𝑠−𝜌)𝑔𝐷𝐵0.6𝐷𝑚0.4

The modified DuBoys equation for flowing water in broad shallow channels relates its bed shear stress 𝑇_𝑐 (N m⁻²) to the fluid density 𝜌 (1000 kg m⁻³), gravitational acceleration 𝑔 (9.8 m s⁻²), flow depth 𝑑 (𝑚), and flow slope 𝑆 (rise:run). The Shields entrainment relations, as modified by Miller [23], and Komar [24, 25], relate bottom shear stress to clast transport, where 𝑇_𝑐 is critical shear stress (dyne cm⁻²), 𝜌_𝑠 is grain density (g cm⁻³), 𝜌_𝑠 is fluid density (g cm⁻³), 𝐷_𝑚 is grain intermediate diameter of the largest clast transported (cm), and 𝐷₅₀ is bed mean grain size (cm).