Rivers and other natural water streams are examples of natural channels usually lined with river rocks and some underwater vegetation. Lining a channel with a smooth-finish concrete or grouted rip rap would allow a faster flow of water compared to a natural channel.

The rougher the surface is, the slower the water flows through it. The material used in the channel construction describes the roughness of the channel surface. In his equation, Manning concluded that the water flow rate depends on the material used in constructing the channel, the channel's cross-sectional shape, and its slope. Manning's equation was developed to fit the data recorded during his time. In the late 19th century, an accountant-turned-engineer named Robert Manning developed an equation that describes the effects of a channel's characteristics on an open channel's water flow rate. In this kind of flow, we can then calculate the dimensions of the chosen uniform shape as long as we have all the other characteristics of the channel. In a steady uniform flow, the flow rate does not change throughout a channel that has uniform cross-sectional shape, slope, and roughness. In this open channel flow calculator, we dive into the simplest form of open channel flow and consider steady and uniform flow. You can learn more about such cases in our pipe flow calculator. There are also some cases wherein water flows due to gravity, but the channel or pipe is filled. On the other hand, we call it an open channel flow when gravity acts in transporting the water, like in rivers or canals where the water flows from a higher to a lower elevation and the surface of the water is 'open' or exposed to the atmospheric pressure. As the pipe cross-section is fully enclosed and not directly exposed to atmospheric pressure, this would be called a closed channel. In this case, water will fill the pipes as it travels upwards. The water pump would push the water up the pipes by applying a large amount of pressure to the water through mechanical action, usually by centrifugal force. If we want to bring water up a building, we could do this with a powerful water pump. Transporting water from one place to another can be done in two ways – with the help of pressure or with the help of gravity.

Concrete flume calculator