1.3 River Landscapes & Processes

• Fluvial means related to rivers
• The three fluvial processes which shape a river channel are:

  • Erosion
  • Transportation
  • Deposition
• About 95% of a river's energy is used to overcome friction.
• Erosion involves the movement of material. This is what makes it different from weathering, which happens ' in situ '.
• The four erosion processes that change a river channel are: HACA

  • Hydraulic action
  • Abrasion
  • Attrition
  • Corrosion/solution
• Traction is the transportation of particles by rolling along the river bed
• Saltation is the bouncing movement of particles along the river bed.
• Deposition occurs when the river's velocity slows down and it can no longer transport its load.
• Soft rocks erode more rapidly than hard, resistant rocks.
• Discharge is the volume of water flowing through a river channel at a specific point over a given time period.
• A long profile shows the changes in a river's gradient from source to mouth.
• Most long profiles have a concave shape.
• A cross profile is a cross-section from one bank of a river to the other
• The River Tees source is 754 metres above sea level.
• Interlocking spurs are found in the upper course where the river starts to meander, forming ridges on alternating valley sides
• In the upper course, rivers are narrow and shallow.
• In the middle course, the river channel becomes wider and deeper.
• Meanders increase in size with distance downstream.
• The depositional landforms found in the lower course of the river are:

  • Floodplains
  • Natural levees
  • Deltas
• Sediment and alluvium make up most of the bedload in the lower course of the river.
• A drought is a period of hot, dry weather with below-average rainfall.
• Storms result in high rainfall levels, increasing the amount of water (discharge) in rivers and the risk of flooding.
• Droughts dry out the soil and make it impermeable, decreasing infiltration and increasing surface runoff and river discharge.
• Evaporation is the process of liquid water changing into water vapour
• The frequency of major storms has increased in the UK. Between 2010 and 2014, there were 10 major storms. Between 2015 and 2020, there were 42 major storms.
• The UK has a temperate climate
• The term used to describe the erosion of the soft rock underneath the hard rock in waterfall formation is undercutting.
• Abrasion is one of the main erosional processes in the formation of waterfalls and gorges.
• A V-shaped valley is formed by vertical erosion cutting down into the river bed and deepening the river channel, while weathering and mass movement lead to material from the valley sides collapsing into the river, forming steep sides
• A meander is a bend in a river. The fastest flow on the outside of the bend leads to erosion and the formation of a river cliff. The slower flow on the inside of the bend leads to deposition and the formation of a slip-off slope.
• A levee is a natural embankment formed along the banks of a river by the deposition of sediment during flooding.
• A floodplain is a flat expanse of land on either side of the river, formed by the migration of meanders together with the deposition of sediment during flooding.
• Alluvium is the lighter materials, such as gravel, sand, and silt, carried and deposited by a river
• During the formation of an oxbow lake, the water usually breaks through the neck of a meander during a flood. This is the only time there is sufficient erosive power.
• Urbanisation increases the amount of impermeable surfaces, leading to water flowing into drains and reaching rivers more rapidly, increasing the risk of flooding.
• Agriculture, such as clearing vegetation for crops and grazing, reduces interception and infiltration, increasing surface runoff and the amount of water reaching rivers.
• Abstraction is the removal of water from a river for purposes such as irrigation or industry.
• Abstraction reduces the discharge in the river, which may lead to increased deposition and a decrease in erosion.
• Lag time is the time between peak rainfall and peak discharge, as shown on a flood hydrograph.
• The recessional limb is part of a flood hydrograph that shows the decrease in river discharge after the peak discharge.