During border strip surface irrigation, water flows as a thin sheet over the soil surface. Because water infiltrates into the soil continuously along the path of advance, the discharge rate decreases along the flow length ($dQ/dx \lt 0$, spatially varied flow). Furthermore, at any given cross section, the depth and flow velocity vary over time ($dQ/dt \ne 0$). Therefore, overland flow in a border strip is an example of spatially varied unsteady flow with decreasing discharge.