how to write expression for flc2hs?

Hi Comsolers,

I have an expression which is 1.112e-4*(U_esvr>=1.112e-4)+0.0*(U_esvr<1.112e-4).

I want to use heaviside step function, so how can I write it in flc2hs?

Information: working with fluid flow-porous media and subsurface flow-richards' equation, I want to calculate the infiltration rate during time. exactly like this graph (Attached)

Thanks in advance for your help.
Sepideh