ABSTRACT
Rivers, streams, aqueducts, drainage and irrigation ditches, and sewer pipes most often flow only partially full. Open Channel Flow exists in these conduits where the water has a free surface exposed to atmospheric pressure. Water depth being constant from one point to another, there is no pressure to act as the driving force. The only natural energy this water possesses is its Velocity Head, and at normal water velocities this is a small value. Open channels have a degree of roughness, just as water pipes under pressure do, and friction occurs as the moving water rubs against the sides of the channel. This quickly depletes the Velocity Head, and decreases the velocity. In open channels, maintenance of proper velocity is of prime importance. In order to keep the velocity constant, the channel slope must be adequate to overcome friction losses. Calculation for head loss at a given flow is necessary, and the Hazen-Williams formula is useful.
