Lateral flow give a huge impact to the both of steady and unsteady flow in the channel. Lateral flow commonly come from the smaller channel in a junction or from an outlet of retention pond. Lateral flow will give an impact to the original flow in a form oh higher water surface elevation, higher speed, or both of them. To further learning about it, we need to learn how lateral flow react at the peak of hydrograph and at the end of hydrograph. Furthermore we also need to learn how it react to tidal while it position is at the end of hydrograph and at the peak of hydrograph.