# Wash-off

A portion of the bacteria on plant foliage may be washed off during rain events. The fraction washed off is a function of plant morphology, bacteria characteristics, and the timing and intensity of the rainfall event. Wash-off will occur when the amount of precipitation on a given day exceeds 2.54 mm.

           The amount of bacteria washing off plant foliage during a precipitation event on a given day is calculated:

$$bact\_{lp,wsh}=fr\_{wsh,lp}\*bact\_{lp,fol}$$                                            3:4.1.1

$$bact\_{p,wsh}=fr\_{wsh,p}\*bact\_{p,fol}$$                                               3:4.1.2

where $$bact\_{lp,wsh}$$ is the amount of less persistent bacteria on foliage that is washed off the plant and onto the soil surface on a given day (# cfu/m$$^2$$), $$bact\_{p,wsh}$$ is the amount of persistent bacteria on foliage that is washed off the plant and onto the soil surface on a given day (# cfu/m$$^2$$), $$fr\_{wsh,lp}$$ is the wash-off fraction for the less persistent bacteria, $$fr\_{wsh,p}$$ is the wash-off fraction for the persistent bacteria, $$bact\_{lp,fol}$$ is the amount of less persistent bacteria attached to the foliage (# cfu/m$$^2$$), and $$bact\_{p,fol}$$ is the amount of persistent bacteria attached to the foliage (# cfu/m$$^2$$). The wash-off fraction represents the portion of the bacteria on the foliage that is dislodgable.

          Bacteria that washes off the foliage is assumed to remain in solution in the soil surface layer.

Table 3:4-1: SWAT+ input variables that pertain to bacteria wash-off.

| Variable Name | Definition                                                       | Input File |
| ------------- | ---------------------------------------------------------------- | ---------- |
| WOF\_P        | $$fr\_{wsh,p}$$: Wash-off fraction for persistent bacteria       | .bsn       |
| WOF\_LP       | $$fr\_{wsh,lp}$$: Wash-off fraction for less persistent bacteria | .bsn       |