Assigning dye of different diffusivities in a 1 D channel


I want to use the dye of different diffusivities in my EFDC model to analyze the transport phenomenon. I want to run for different diffusivities for example 10 m2/s , 15 m2/s, 0.1 m2/s etc. Then I would compare the results obtained by EFDC with the analytical advection diffusion equation. So, in order to compare the results with the advection diffusion equation the first thing we need to obtain is constant velocity condition because in analytical advection diffusion equation constant velocity is used as initial condition or user specified. I want to know how exactly we specify the particular diffusivity (for example 15 m2/s) for the dye. For example if I want to specify diffusivity 15 what parameter do I change to 15 ? Do I change background horizontal eddy viscosity ? I tried changing all the parameters such as ABO, AVO, AHO, AHD. It seems AHO seems to give the good results but when I change the AHO value, then the velocity distribution of the water would be changed. I just want to specify the diffusion coefficient for the dye. How do I achieve this ?


Thank you for your question. Basically, under EFDC Hydrodynamic Options > Turbulent Diffusion you to need to set the background/constant horizontal eddy viscosity to the constant that you want eg 15. Then you should set the AHD (Smagorinsky’s coeff) to 0 to use the constant viscosity option. Finally, you should set ISHMD = 2, which is the radial checkbox “Activate HMD with Smagorinsky, Wall Drag and WC Diffusion”.