Reynolds Number formula:
  N_R = ρ * v * D / η
where:
  N_R: Reynolds Number, dimensionless
  ρ: Fluid Density, in Kg/m^3
  v: Fluid Speed (velocity), in meter/second
  D: Pipe Diameter (travelled length of the fluid; hydraulic diameter in river system), in meter
  η: Fluid Viscosity, in N.s/m^2