Question

what is the difference between seepage velocity and discharge velocity​

Answer 1

Seepage velocity is velocity of groundwater measured from Darcy's law.

Its not real velocity of water in pores but apparent velocity through bulk of porous medium.

Actual velocity is higher than seepage velocity by factor which joins effects of porosity and tortuosity of actual flow path around mineral grains.

Discharge velocity is rate of flow of liquid across given cross sectional area though not necessarily into the ground.  

Seepage velocity is velocity of groundwater which is calculated using Darcy's law.

Its velocity which ground water goes through porous medium i.e. soil and rocks.