Section 4.6 - River Landscapes/Processes Flashcards
What is meant by the long profile of a river?
The long profile of a river shows the gradient changes along the river course
How does the River Eden’s landscape change along its long profile (upper/middle/lower course) considering channel shape, valley profile, gradient, discharge, velocity and sediment size and shape?
The source of the River Eden is around 600m above sea level. The valley is steep sided with a narrow and shallow river channel with a steep gradient. The river has a low velocity due to friction on the rough channel sides and bed. The river carries large angular stones
In the middle course, the rivers basin is made from sandstone, easily eroded by the river. This results in more lateral erosion widening the river. The channel is at a much lower gradient, as well as being wider and deeper with a higher discharge due to tributaries joining. The river now carries much smaller and rounded rocks.
In the lower course of the river, the valley is very wide and flat. The river has a high velocity as there is very little friction from the smooth channel sides. The river also has a very high discharge as two other rivers join. The channel is very wide and deep (up to 50m wide in Carlisle) The material carried is well rounded and fine carried through suspension or solution.
Why does river discharge increase towards the lower course of the river Eden?
Upon descending the river, many tributaries join with the River Eden. These tributaries increase discharge.
What happens to sediment size upon descending the river? Why?
The particle size decreases when descending the river because of increased levels of abrasion and attrition.
What happens to the velocity of the river when descending the course? Why?
The river velocity increase when descending the river because the edges become much smoother, and there is less friction slowing the water down.
Compare hydraulic action with abrasion
Hydraulic action is the force of the water breaking rock particles away from the river channel, whereas abrasion is the action of rocks picked up by the river being scraped along the channel wearing it away
Give the definition of weathering on rivers
Weathering is the breaking down of rocks on the sides of the river valley
Compare freeze-thaw and biological weathering
Freeze-thaw weathering is water getting into cracks, freezing and expanding, melting but remaining in the cracks and the repeat of this process that eventually can break away large chunks of rock. Biological weathering can be plant roots or animals digging in to the ground for a stable base or for shelter, that inadvertently breaks up rock
Compare traction with suspension transport
Traction is where large rocks are rolled along the river bed, pushed by the force of the water. Suspension is small particles such as clay and silt that are carried along by the river.
Explain the formation of a waterfall.
A waterfall is formed when a river runs over an area of hard rock followed by an area of hard rock followed by an area of soft rock. The soft rock is eroded by hydraulic action and abrasion creating a step in the river. The water erodes the soft rock as it goes over the step and eventually a steep drop is created. The hard rock is undercut by the water in the pool beneath the steep drop and as it becomes unsupported it collapses. The sediment swirls around beneath resulting in abrasion forming a plunge pool. Over time, continued undercutting causes more rock to collapse, the waterfall retreats forming a gorge
Describe the formation of ox-bow lakes
Ox-bow lakes form within meanders. Erosion causes the outsides of the bends to get closer until a small (neck) section of land remains between. The river eventually breaks through this neck and flows along the fastest course (through the straight section newly broken) The meander is then cut off because of deposition and this forms an
ox-bow lake.
Describe the formation of interlocking spurs
In the upper course of s river, the erosion is predominantly vertical. This creates steep sided v-shaped valleys. As the rivers are not powerful enough to erode laterally, they have to wind around the high hillsides sticking out either side. The hillsides interlock as the river winds around them and this forms the interlocking spurs
Describe the formation of floodplains
A floodplain is the wide valley floor in either side of the river that occasionally gets flooded. As the river floods over onto the floodplain, it slows down and deposits material. This builds up and raises the floodplain. Meanders move across the floodplain widening it. The downstream movement of meanders flattens out the valley floor. The deposition on the slip-off slopes of meanders also builds up the floodplain.
Describe the formation of leeves
During a flood, eroded material is deposited over the whole floodplain. Over time, the deposited material builds up forming levees along the edge of the channel
Describe the formation of deltas
Rivers are forced to slow down as they meet the sea or a lake, causing them to deposit material. If the material is not washed away by the sea, it blocks up the river. The river then has to split up forming distributaries. As the material builds up, it eventually creates flat, low lying areas of land called deltas
