Bedrock river

Stream power is the process energy from the water converted into kinetic energy due to the steepening in slope. When water is being transported down a channel, it is doing so by gravitational potential energy.[2] Due to the laws of conservation of energy, energy that is lost traveling downstream must be transformed into another type of energy. The energy form that is it transformed into is the kinetic energy of the water beating on the bedrock.[2] The rate of the potential energy loss is calculated in the stream power of the river. The stream power equation is:

${\displaystyle \Omega =\mathrm {\rho {}gQS} }$[1]

where:

${\displaystyle \Omega }$ = stream power

${\displaystyle \rho }$ = water density

g = gravitational constant

Q = hydraulic discharge of the stream (m³/s)

S = slope of the channel

This equation suggests that stream power might be the single most important factor in bedrock incision. In an alluvial river the stream power would be more of a transport because it would be picking up loose material and depositing it, but with a constant influx of sediment it would not be incising.[3]

Abrasion is the process by which sediments are transported in the flow. The rate of erosion done using abrasion is affected by the strength of the bedrock.[3] Abrasion is also affected by the amount of sediment load present in the river. Too much sediment and most of the particles will not have enough energy; too little and not enough of the particles will come into contact with the bed. The process can erode individual grains, or flakes from the rocks surface.[3] The most common indicators of abrasion is potholes in the bedrock or a trough-like shape to the river. There are three types of sediment transport in a fluvial process: dissolved load, suspended load, and bed load.[2] The process that most affects a bedrock river is the suspended load.[2]

Suspended load is the grains that are light enough to be carried in the water and do not contact the bed of the river unless there is an obstruction or topographic change in the bed. The way these particles erode a bedrock river is by contact with these obstructions. Being as they are carried as part of the river flow they have a significantly higher kinetic energy and coming into contact with an abnormality in the river bed can cause more damage than a larger grain with lower energy.[1] The grain size that is normally held in the suspended load ranges from very fine to fine; clays and silts.

Bedload erosion can also be a major factor in bedrock erosion. It is caused by saltating grains or traction.

Saltating is where the grains are lifted up by the water and then tossed back down. Most of the time this is with gravels and if the stream power is big enough pebbles. However the clays and silts have too much cohesion to be transported by this method. When the particles come into contact with the bedrock they slowly wear away at its surface. They can gradually form micro-cracks or extend already existing cracks. The physics behind this erosional process states: the mass of the rock worn away by the incoming particle is directly proportional to the kinetic energy of that incoming particle.[2]

Traction is where the sediment is too large to be picked up in the river flow but is small enough to be pushed or rolled along at a slower rate. Traction is covered in quarrying.

Quarrying (also known as plucking) is the process by which a chunk of the bedrock must be somehow removed from the bed of the river and then forced along the planar surface of the riverbed.[1] This process is the most similar to glacial erosion.[2] It is most effective in rivers where the jointing is close enough to allow the blocks to be moved by river flow.[1]

The process of removing the piece of bedrock can be caused by many different factors. A crack or a flex in the bedrock will initially make a disconnected piece of the bedrock.[2] Then, either by hydraulic wedging or frost-cracking the block can be forced out.[2] If the bedrock is already highly jointed, fractured or a bedding plane it will be easier for the chunk to be removed.[1] Highly jointed or bedding plane bedrock can make it easier for the blocks to be lifted or shifted out of their position. Scientists believe that this happens because of the weathering of joints surfaces.[1] Subsequently, the joints are wedged apart and might be weakened by being bombarded by bedload particles.[1]

Once the block of bedrock is removed it must then be pushed along the bed of the river. In order for this to happen the shear stress of the river on the top of the rock must exceed the frictional forces on the bottom of the rock. The blocks will eventually erode, but will cause headward erosion of the river while it exists.

Wedging is the process by which small cracks appear in the bed of the river which are enlarged by smaller particles.[1] It can cause large blocks of the river to be removed from the bed starting the quarrying process. The initial cracks appear due to a flux in the bedrock itself which is caused by a "rapid and large pressure variation".[1] These can be caused by mass movements, or heavy storms. After the initial crack is made a small amount of sediment, sometimes no more than a grain, is passively deposited in the crack.[1] When the bedrock flexes back into its original position the crack is left open due to the wedging. Gradually as more sediment accumulates in the crack it will widen and deepen. This is more common in an already jointed river bed.[2]

Dissolution is the process by which the downstream change in the solute concentration is controlled by the dissolution rate of the rock.[1] This process typically only affects a bedrock river when the rock is already prone to dissolution, such as a sandstone.[1] One would be most likely to see this in caves made up of carbonate rocks.[1] Some other factors that this process is dependent on are "the ratio of mineral surface are to water volume, the degree of chemical under-saturation, and the time it takes a water parcel to move through a reach."[2] It is one of the least likely forms of incision but it does play a role in the process.