Temperature Effects in Low-Transport, Flat-Bed Flows

Experimental data show that a dimensionless bed-load discharge q_*b = q_b/U_*b D_g can be expressed as a function of a boundary Reynolds number R_*b = U_*bD_g/ν and a dimensionless shear stress τ_*b = τ_ob/(γ_s-γ)D_g in which q_b = bedload discharge in volume per unit-width and time; U_*b = (τ_ob/ρ)^1/2 = shear velocity; τ_ob = bed shear stress; ρ = density of the water; D_g = geometric mean size of sediment, ν = kinematic viscosity in the water, and γ and γ_s are, respectively, the specific weight of water and sediment. Contours of Q_*b plotted on a Shields graph (i.e., τ* vs R_*b) have the same shape as the Shields curve and the contour, q_*b = 10^-2, follows it closely. The effect of temperature on τ_o and q_sb is shown by the data. For R_*b < 20 increase in the temperature of a flow results in a decrease in τ_o and τ_*b and an increase in R_*b, q_sg and q_*b. For 20 < R_*b < 200 an increase in water temperature results in an increase in τ_ob, τ_*b and R_*b and a decrease in q_sb and q_*b > 200 there is no temperature effect.