Please enable JavaScript.
Coggle requires JavaScript to display documents.
Physical Landscapes in the UK - Rivers - Coggle Diagram
Physical Landscapes in the UK - Rivers
Meanders
Ox-bow Lakes
Meanders get larger over time - they can eventually turn into an ox-bow lake:
Erosion causes the outside bend to get closer until there's only a small bit of land between the bends (called the neck)
The river breaks through this land, usually during a flood and the river flows along the shortest course
Deposition eventually cuts off the meander forming an ox-bow lake, e.g. the River Calder has formed several ox-bow lakes near Castleford, West Yorkshire
Rivers develop large bends called meanders in their middle and lower courses, in areas where the channel has both shallow and deep sections:
The current is faster on the outside of the bend because the river channel is deeper (there's less friction to slow the water down)
So more erosion takes place on the outside of the bend, forming river cliffs
The current is slower on the inside of the bend because the river channel is shallower (there's more friction)
So eroded material is deposited on the inside of the bend, forming slip-off slopes
Waterfalls
Waterfalls form where a river flows over an area of hard rock followed by an area of softer rock
The softer rock is eroded more (by hydraulic action and abrasion) than the harder rock creating a step
As water flows over the soft rock it is eroded more and more creating a steep drop
The hard rock is eventually undercut, is left unsupported and collapses
The collapsed rock is swirled around the foot of the fall eroding it (abrasion) creating a deep plunge pool
Over time more and more undercutting causes more collapses. The waterfall retreats leaving a steep sided gorge
River Profiles and Courses
Profiles
Long Profile
Shows the gradient of the river
Cross Profile
Shows the valley and channel shape
Courses
Upper - Steep, V-shaped valley, steep sides, narrow, shallow channel
Middle - Medium, gently sloping valley sides, wider, deeper channel
Lower - Gentle, very wide, almost flat valley, very wide, deep channel
Floodplains, Levees & Estuaries
Floodplains
The flood plain is the wide valley floor on either side of a river which occasionally floods
When rivers flood, the water slows down, loses energy and deposits the material that it's transporting. This builds up the flood plain
Meanders widen as they migrate across floodplains laterally.
Overtime, meanders also migrate downstream
The deposition that happens on the slip-off sloped of meanders also builds up the flood plain
Levees
Levees are natural embankments along the edges of a river channel
During a flood, eroded material is deposited closest to the river channel, because it gets dropped first when the river slows down and loses energy
Over time, the deposited material builds up, creating levees along the edges of the channel
Estuaries
Estuaries are found at river mouths. The land is close to sea level and the river valley is at its widest
The water here is tidal - the river level rises and falls each day
When the water floods over the banks of the river, it carries silt and sand onto the valley floor
As the tide reaches its highest point, the water moves slowly and has little energy, so it deposits sediment
Over time, more mud builds up, creating large mudflats, e.g. the Severn Estuary, Gloucestershire
At low tide, the wide, muddy banks are exposed
Erosion, Transportation, Deposition
Four Processes of Erosion
Hydraulic action - The force of the river water colliding with the rocks breaks rock particles away from the river channel
Abrasion - Eroded rocks picked up by the river scrape and rub against the channel, wearing it away. Most erosion happens by abrasion
Attrition - Eroded rocks picked up by the river crash into each other and break into smaller fragments. Their edges also get rounded off as they rub together. The further the material travels, the more it is eroded - attrition causes particles size to decrease from a river's source to its mouth
Solution - River water dissolves some types of rock, e.g. chalk and limestone
Transportation
Traction - Large particles like boulders are pushed along the river bed by the force of the water
Saltation - Pebble-sized particles are bounced along the river bed by the force of the water
Suspension - Small particles like silt and clay are carried along by the water
Solution - Soluble materials (e.g. limestone) dissolve in the water and are carried along
Deposition
Deposition is when a river drops the material it's transporting. It occurs when a river loses velocity and energy. There are a few reasons why rivers slow down and deposit material:
The volume of water falls e.g. after a time of flood
The amount of eroded material increases
The water is shallower, e.g. on the inside of a bend
The river reaches its mouth
Vertical and Lateral Erosion
Vertical erosion - This deepens the river valley and channel, making it V-shaped. It's dominant in the upper course of the river. High turbulence causes the rough, angular particles to be scraped along the river bed, causing intense downwards erosion
Lateral Erosion - This widens the river valley and channel during the formation of meanders. It's dominant in the middle and lower coursed of the river
Hard & Soft Engineering Strategies
Hard
Man-made structures built to control the flow of rivers and reduce flooding
Dams & Reservoirs
Barriers are built across the upper course of a river storing water behind the wall
Store water after heavy rain and prevent flooding downstream, can be used to generate HEP
Can flood existing settlements upstream, extremely expensive
Channel straightening
Meanders are removed by building straighter artificial channels
Water leaves the area quicker rather than building up
Flooding may happen downstream instead
Soft
Schemes set up using knowledge of a river and its processes to reduce the effects of flooding
Flood Plain Zoning
Restrictions prevent building on parts of a flood plain that are likely to be affected by a flood
Flood risk is reduced as fewer impermeable surfaces are created e.g. roads. The impact of flooding is also reduced - there are no buildings to damage
The expansion of an urban area is limited if there aren't any suitable building sites
Planting Trees
Planting trees in the river valley increases the interception of rain water therefore increasing lag time
Discharge and flood risk decreased, provides habitats for wildlife
Less land available for farming
River Discharge and Flooding
River Discharge
Peak discharge - The highest discharge in the period of time you're looking at
Lag time - The delay between peak rainfall and peak discharge
Rising limb - The increase in river discharge as rainwater flows into the river
Falling limb - The decrease in river discharge as the river returns to its normal level
Factors affecting flooding
Physical
Heavy rainfall - Heavy rainfall means that water arrives too quickly to infiltrate, so there's a lot of surface runoff, which increases discharge
Prolonged Rainfall - Prolonged rainfall can saturate the soil. Any further rainfall can't infiltrate, increasing runoff into river channels
Geology - Clay soils and some rocks e.g. granite and shale, are impermeable so runoff is increased
Relief - If a river is in a steep-sided valley, water will reach the river channel quicker because it can flow faster down the steep slopes - this rapidly increases the discharge
Human
Buildings are often made from impermeable materials e.g. concrete and surrounded by roads made from impermeable surfaces e.g. tarmac increasing surface runoff. Man-made drains then quickly transport runoff to rivers, increasing discharge
Trees intercept rainwater in their leaves, which then evaporates. Trees also take up and store water from the ground. This means that cutting down trees increases the volume of water that enters the river channel
Case Study: River Tees
Facts
137km long, rising in Pennines
Upper course: V-shaped valleys interlocking spurs
High Force waterfall tallest in England (21m) - horizontal cap of Whinstone over Carboniferous limestone
Middle course: meanders, floodplain at Barnard Castle
Lower course: ox bows, levees, estuary, mudflats at Teesmouth (Middlesborough)
Petrochemical and nuclear plant at mouth
Seal Sands protected for wildlife
Management Scheme
23,000 people at risk of flooding
Town of Yarn - £11 million invested in flood gates, gaboon's, flood warnings, flood plain zoning
Tees Barrage - reduces coastal flooding
Cow Green Reservoir - helps to reduce flooding downstream and provides 30 hectares of natural habitat for wildlife