Bulk properties refer to properties of the sediment-water mixture. Bulk properties usually refer to sediment bed properties such as porosity, bulk densities, and erodibility parameters. The erodibility parameters are discussed in a subsequent section while the porosity and bulk densities are covered below.
Density
The wet bulk density is density of the water-sediment mixture and is defined as
1) |
\rho _{m}=\frac{m}{V}=\frac{m_{w}+m_{s}}{V} |
where
m = mass of water-sediment mixture [M]
m_{w} = water mass [M]
m_{s} = sediment mass [M]
V_{} = total volume of sediment mixture [L3]
The wet bulk density is usually utilized for describing the density of the transported water-sediment mixture. Given a fractional sediment concentration with varying grain densities, the density of the water-sediment mixture can be computed as
2) |
ρ_m = ρ_w(1 − c) + ∑_kρ_{sk}c_k |
where
ρ_{m} = water-sediment mixture density [M/L3]
ρ_{w} = water density [M/L3]
c = ∑_kc_k = sediment volume concentration [-]
ρ_{sk} = grain class particle density [M/L3]
c_{k} = grain class (fractional) volume concentration [-]
Wet bulk densities can vary from 1330 kg/m3 to 2230 kg/m3.
Viscosity
Thomas (1965) proposed the following equation for the water-sediment mixture viscosity
3) |
\frac{\mu _{m}}{\mu _{w}}=1+2.5c+10.05c^{2} |
where
μ_{m} = water-sediment mixture viscosity [M⋅T/L]
μ_{w} = water viscosity [M⋅T/L]
c = sediment volume concentration [-]
The above equation has an accuracy of 97.5% for c < 0.25%.