i have checked out the manual.
where can i find the formular of dye decay or reference ?
Usually, the decay of fecal coliform or dye can be expressed as:
where C = dye concentration, Co = initial concentration, k = decay rate and t = time.
In EFDC model, you can specify the decay rate using a parameter RKDYE. If you specify RKDYE < 0 then it will be the decay rate.
A small chunk of code showing how DYE is updated in EFDC model is shown below:
IF(RKDYE < 0.0)THEN
! Now update the DYE concentration
In the above code, you can see that when RKDYE is smaller than 0 then the temporary variable CDYTEMP is calculated which is similar to the equation that I provided in the starting section. Then, the dye concentration at each cell are updated by multiplying the dye concentration with the temporary variable.
Details of these calculations can be found on calconc.f90.
I hope this is helpful for you to understand how the decay rate is being used in the model.