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What factors influence how much energy a river has?

What factors influence how much energy a river has?.

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What factors influence how much energy a river has?

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  1. What factors influence how much energy a river has?

  2. This simple diagram illustrates that there is a relationship between the amount of energy a river has (a product of its volume, speed and gradient) and the amount of work it can do (expressed as its ability to overcome the friction of its bed and banks and to carry out erosion and transport of materials).  Rivers achieve their work (effects) by using the energy available to them.  The potential energy, or stored energy, that is available is proportional to the height above seal level.  As water moves down slope, potential energy is converted to kinetic energy which is used to carry out the river's tasks.  In the transfer from potential to kinetic most of the energy is lost as heat owing to friction encountered as the water move.  Some 95% of a river's energy is used in this way, leaving just 5% to carry out erosion and transport of debris.    The ability of a stream to erode and transport material depends on its velocity.Some sluggish streams flow at rates of less than 1 kilometer per hour, whereas more rapid ones may exceed 30 kilometers per hour.Three key factors determine the velocity of a stream.These are: 1. gradient; 2. channel characteristics - the shape, size and roughness of the channel; 3. discharge.

  3. River Gradient | Channel Roughness | Channel Shape | In figure A, the channel is smooth while that in figure B is rough or uneven with boulders on the river bed as well as rocks that protrude out from the bank. A river that flows through such a river has to overcome such obstacles and therefore there will be more friction and the velocity of the river is reduced.Fig A                                                                   Fig B

  4. | The shape of the channel or its cross section affects the wetted perimeter. The wetted perimeter refers to the extent to which water is in contact with its channel. The greater the wetted perimeter, the greater the friction between the water and the banks and the bed of the channel, and the slower the flow of river. Wetted perimeter is calculating by adding the length and the breadth of the channel in contact with water

  5. Channel characteristics also affect a stream’s velocity.Larger channels have more efficient flow because a smaller proportion of water is in contact with the channel.As well, a smooth channel promotes more uniform flow and hence a greater velocity.

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