Revised functions of reduction efficiencies of infiltration trenches, swales and grass ditches after a supplementary literature study of the surface area that these facilities normally occupies of the reduced catchment area.
Comments: This gives lower treatment effects than before the revision. Efforts to find such good relationships as possible for the calculations will continue.
As previously noted, the uncertainty is relatively large in calculating treatment effects from these facilities, especially when they are based on a function of the drainage basin size.
The database has been supplemented with uncertainty estimates for these and other types of treatment facilities, so the file can be downloaded from the flowchart, after which one can compare the calculated effects with the database values.
If necessary, you can contact us or input your own values based on an assessment of both the calculated effects and the values that exist in the database.