Describe and explain how river processes change along a river’s long profile
Activity:
Describe and explain how river processes change along a river’s long profile (15 MARKS)
Upper - Erosion - Vertical - Weak Erosion but strong Velocity
In the upper stage of the river’s long profile, there is mainly vertical erosion and by abrasion. Erosion occurs when there are high-energy conditions and discharge are high after heavy rain or ice melt. The rough channel from the high velocity causes turbulence and the large, angular bedload is dragged along the river bed, causing intense downwards (vertical) erosion. Mainly large particles such as boulders carried by traction or saltation during high-energy conditions. There is little deposition in the upper course of the river and is mainly the largest particles being deposited in the river bed as energy levels drop.
The middle stage features mainly lateral erosion this is due to the rivers channel slightly flattening out as it goes down. Attrition of larger particles in this stage means that sediment particle size decreases from source to mouth. More material carried in the river’s suspension as particle sizes decreases due to a higher level of erosion. Some larger particles are moved by saltation. This therefore means particles such as sand and gravel are deposited across the flood plain as the river floods and friction reduces the river’s energy.
Although the velocity and discharge are at their highest in the lower stage of the river’s long profile. There is generally less erosion because turbulence is lower and sediment particle size is reduced (due to reduced abrasion technique). Some lateral erosion occurs during the formation of meanders in the lower stage of the river. Mainly smaller particles such as silt and clay are generally transported by suspension in the lower stage. However there are other such substances carried in solution. Deposition does occur but it is generally smaller particles such as sand, silt and clay, these are usually deposited on the flood plain when the river
Describe and explain how river processes change along a river’s long profile (15 MARKS)
Upper - Erosion - Vertical - Weak Erosion but strong Velocity
In the upper stage of the river’s long profile, there is mainly vertical erosion and by abrasion. Erosion occurs when there are high-energy conditions and discharge are high after heavy rain or ice melt. The rough channel from the high velocity causes turbulence and the large, angular bedload is dragged along the river bed, causing intense downwards (vertical) erosion. Mainly large particles such as boulders carried by traction or saltation during high-energy conditions. There is little deposition in the upper course of the river and is mainly the largest particles being deposited in the river bed as energy levels drop.
The middle stage features mainly lateral erosion this is due to the rivers channel slightly flattening out as it goes down. Attrition of larger particles in this stage means that sediment particle size decreases from source to mouth. More material carried in the river’s suspension as particle sizes decreases due to a higher level of erosion. Some larger particles are moved by saltation. This therefore means particles such as sand and gravel are deposited across the flood plain as the river floods and friction reduces the river’s energy.
Although the velocity and discharge are at their highest in the lower stage of the river’s long profile. There is generally less erosion because turbulence is lower and sediment particle size is reduced (due to reduced abrasion technique). Some lateral erosion occurs during the formation of meanders in the lower stage of the river. Mainly smaller particles such as silt and clay are generally transported by suspension in the lower stage. However there are other such substances carried in solution. Deposition does occur but it is generally smaller particles such as sand, silt and clay, these are usually deposited on the flood plain when the river