Hello, I am curious about the Richardson number formula in EFDC. I couldn’t find that information in the user guides. I checked basic equations other textbooks, however I don’t know which formula is applied in EFDC.

The Richardson number is used to calculate diffusivity and turbulence viscosity. The equation for the Richardson number can be found on page 11 of this document in the installation direction of EE:

EFDC_1_Hydrodynamics_&_Mass_Transport_Manual.pdf

In the code it is in the subroutine calavb as the variable RIQ. Note that q^2 is the turbulence intensity, and l is the turbulence length scale. These are two variables in Mellor-Yamada equations. The solution of Mellor-Yamada equations include q^2 and l, and from these Richardson number is calculated.