The focus of this chapter is to scrutinize unsteady viscous laminar flow of an incompressible viscous fluid down an unclosed inclinable channel with plane porous bottom and non-conducting vertical walls under the action of gravity analytically. The free side is disclosed to atmospheric pressure and an identical tangential stress in the direction of flow. Flux when the tangential stress applied at the free surface is zero is also calculated. The volume rate of flow thereon the cross-section of the channel perpendicular to the x-axis is derived taking special case i.e. f(t) = e-αt. The results obtained in the present paper are in full agreement with the theoretical and empirical established also.