1C: Physical Landscapes in the UK - Rivers Flashcards
Define interception
When raindrops are prevented from falling directly onto the soil surface by the presence of a layer of vegetation
Define infiltration
The passage of water into the soil
Define percolation
The downward movement of water through the rocks, eventually this water becomes groundwater
Define throughflow
Water moving down hill beneath the surface of the soil (it moves gradually through the tiny air spaces between the soil particles)
Define groundwater
Water that collects in rocks deep underground
Define the water table
The line which marks the upper limit of the groundwater (below this line the rocks are saturated with groundwater)
Define erosion
The wearing away and removed of material by a moving force, such as a flowing river
Define lateral erosion
The river erodes the banks of the river. This makes the channel wider
Define vertical erosion
The river cuts down vertically eroding the river bed. This often forms V-shaped valleys
Define hydraulic action
The force of the river against the banks can cause air to be trapped in cracks and crevices. The pressure weakens the banks and gradually wears them down
Define abrasion
Rocks carried along by the river wear down the river bed and banks
Define attrition
Rocks being carried by the river smash together and break into smaller, smoother and rounder particles
Define solution
Soluble particles are dissolved by the river water
Define traction
Heavy rocks and boulders are rolled along the river bed. Happens most in times of flood when the river has more energy
Define saltation
Small stones and pebbles are bounced along the river bed. It can take place when the river energy is lower
Define suspension
Very small particles of sand or clay are ‘suspended’ in the water.
Define deposition
- Deposition occurs when the velocity of a river decreases. It no longer has enough energy to transport sediment so it is deposited
- Large rocks are deposited in the upper course. They are only transported short distances, mostly by traction, during periods of heavy flow
- Finer sediment is carried further downstream, mostly held in suspension. This material will be deposited on the river bed or banks, where velocity is slowed by friction
- A large amount of deposition occurs at the river mouth, where the interaction with tides, along with the very gently gradient, greatly reduces the river’s velocity
River Tees upper course
Altitude: 600m
Landforms: V-shaped valleys, gorge in front of High Force
Energy: High levels of erosive power cutting V-shaped valleys
Bedload: Big and angular boulders
Land use: Reservoirs, farmland, villages, pastoral farming (animals)
River Tees middle course
Altitude: 300-100m
Landforms: Flatter valley, wider meanders, larger flood plains, oxbow lakes
Energy: Lots of lateral erosion
Bedload: Smaller and rounder
Land Use: Arable farming, towns and villages (Yarm)
River Tees lower course
Altitude: 100-0m
Landforms: Very flat and wide, wide estuary at the mouth at Redcar
Energy: Only enough to move the finest materials
Bedload: Estuary mud and silt
Land Use: Iron and steel works, chemical works, nuclear power station. Urban areas - Middlesborough
Waterfall and Gorge formation
- The river is able to erode the softer rock more easily than the harder, more resistant rock and a ‘step’ forms in the path of the river
- The soft rock continues to be eroded by hydraulic action, abrasion and solution. The ‘step’ has now developed into a waterfall. Erosion at the base of the waterfall creates a deep plunge pool
- The swirling, turbulent water in the plunge pool erodes the soft rock at the back of the waterfall so the hard rock is left overhanging
- As a result of gravity, the overhang collapses into the plunge pool below. The rock is broken up and eventually it is carried away by the river.
- The process of undercutting and collapse of the overhanging rock happens over and over again so that, over time, the waterfall moves upstream
- As the waterfall retreats upstream, it creates a steep sided valley called a gorge of recession
Meanders and Oxbow lakes formation
- Water takes the easiest route - usually to one side of the riffle
- As the water is pushed to one side of the riffle, it erodes the bank creating a river cliff
- Here the water is deepest and therefore has more energy for erosion and less energy is lost through friction
- The water is then pushed down towards the bed of the river where friction slows it down as the river at this point is shallower and therefore has less energy
- As a result the river deposits material creating a slip-off slope on the other side of the channel
- The river continues to flow like this (from side to side) eroding and depositing material creating a sinuous channel as a result of lateral erosion
- Due to erosion on the outside bend and deposition on the inside bend, the meander’s shape will change over time
- Erosion narrows the neck of the meander and the meander moves closer together
- Where there is a very high discharge (usually during a flood), the river cut across the neck, taking a new, straighter route
- Deposition will occur to cut off the original meander, leaving a horse-shoe-shaped oxbow lake
Floodplains formation
- Flood plains form due to deposition and erosion
- The narrow valley is widened as the river begins to erode sideways. A wide, flat area next to the river is created. Lateral erosion and the processes of abrasion and hydraulic action erode the outside bend of a meander.
- Meanders then migrate downstream. When the river overflows, material being carried is deposited as speed and energy is lost. Over time, this sediment forms layers on the flat area on either side of the river
Levées formation
- During times of high discharge, the river floods. The energy of the river decreases as velocity is reduced when the river breaks the banks and spreads onto the floodplains
- Levées form when the river is carrying a large load. Heavier, coarse material is deposited first, at the side of the river channel.
- Smaller material is deposited further from the river where there is no longer enough energy to transport the material
- Subsequent floods result in further deposition on these banks depositing a layer of alluvium (a mixture of clay, silt and sand
