Settling velocity: The main principle involved in the sedimentation tank is to reduce the flow velocity of water which allows the major amount of suspended particles to settle down. The velocity with which the particle is settling is known settling velocity.

Surface loading: the volume of water applied per unit time per unit horizontal surface area is called as over flow velocity or surface loading. It must be less than settling velocity of particles.

$V_d$ = Q / BxL

Surface loading = 12 to 18 $m^3 / day / m^2$

Detention period: The time taken by water to travel from inlet to outlet is termed as detention period or detention time. The allowable detention period in the sedimentation tank is 4 to 8 hours.

Detention Time = volume of tank / discharge = V/Q