Grassed Waterways and Filter Strips

[Mary Proteau]

Hi all, 

I am running a fairly simple and spatially small model on SWAT + and have calibrated. Now I am trying to see the effect of adding filter strips or grassed waterways to this agricultural plot. Nothing will affect the outputs of flow, phosphorus, nitrogen, or sediment, and I am very unclear why. 

There also is no way to indicate which HRUs I would like the filter strips or grassed waterways on, or other designations that would make sense to have, such as a previous version of SWAT where I would designate the day they are put into place. 

Any thoughts on what I may be doing wrong that these interventions are apparently not connected to my model?

Thank you!

Mary