Longitudinal dispersivity

Helllo....again,

I understand that longitudinal dispersivity is dispersivity along mass flux direction, but I dont understand how to calculate this value. The manual states that it is scale dependent, but the equation they use is rather perplexing. Any help in the calculation of this value would be greatly appreciated.


cheers,

drew dressler

The dispersivities are scale dependent and you can make a start-estimate from ex. from Gelhar 1995 (see figure) or do a calibration against some breakthrough curves.
If you don’t have breakthrough curves, than you should do some sensitivity analysis of the parameters

Thanks for your help "fdc"

Scale means, total with of model? or size of elements. my model area is around 1000km2 area. i should put single dispersion value for entire or increasing disperion value from sea boundary to other side of model?

'Scale' means scale of the transport phenomenon you're dealing with. In case of a contaminant plume, this is pretty clear... When simulating concentrations of widely distributed substances, though, it gets fuzzy.