This document provides an overview of open channel hydraulics from Chapter 1 of the reference book "Open Channel Hydraulics" by Ven Te Chow. It defines open channel flow and discusses the types and classifications of open channel flow, including uniform and non-uniform flow, steady and unsteady flow, rapidly and gradually varied flow. It also describes the state of open channel flow in terms of Reynolds number and Froude number, defining laminar, transitional, and turbulent flow as well as subcritical, critical, and supercritical flow.