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How are waterfalls formed?
There’s a horizontal band of more resistant rock positioned over exposed, less resistant rock.
Soft rock is eroded quicker than hard rock (hydraulic action) causing undercutting of the hard rock.
The hard rock overhangs until it can no longer support its own weight and collapses.
Abrasion and hydraulic action vertically erode the soft rock to create a plunge pool.
The process of undercutting and collapse is repeated, resulting in the waterfall’s retreat upstream and the plunge pool getting deeper.
A steep-sided valley known as a gorge is left where the waterfall once was before it retreated.
How are V-shaped valleys and interlocking spurs formed?
The upper course of a river doesn’t have enough energy for suspension of particle and instead transports it using traction or saltation.
This results in vertical erosion of the riverbed.
This creates a V-shaped valley.
If there are areas of hard rock which are harder then the river will bend around them, creating interlocking spurs.
How are meanders formed?
In the middle course, the river gains more water and therefore more energy.
Material can be carried in suspension and this material laterally erodes the river banks, widening the river.
When river flow is stronger on one side, most of the water is pushed to that side, causing increased speed due to less friction.
Lateral erosion via abrasion and hydraulic action on the outside bend causes undercutting of the river bank to form a river cliff.
The inside bend has less water and thus increased friction, so the water slows down, loses energy and deposits material. The build-up of deposited sediment is known as a slip-off slope.
How are oxbow lakes formed?
Due to continued erosion of the outside of a meander and deposition on the inside, the ‘neck’ of land within the meander is narrowed.
Over time, or if there’s a very high discharge (during a flood), the river will cut across the neck to take a new, straighter and shorter route.
Deposition occurs to cut of the original meander, leaving an oxbow lake.
How are floodplains formed?
In a wide, flat valley (interlocking spurs may have been removed by erosion), a river floods
The water which has flowed into the valley is fastest directly next to the river, but the further it travels, the more energy it loses due to friction with the ground and vegetation, so any sediment it was carrying is deposited.
This leaves a layer of sediment over the valley.
After multiple floods, the floodplain is created, which is wide, flat, and very fertile due to the nutrients contained in the deposited sediment.
How are levees formed?
Levees occur in the lower course of a river where there is an increase in volume of water flowing downstream and it floods.
The water which has overflowed loses more energy as it travels further away from the river.
This means that the largest material is deposited first on the sides of the river banks whereas smaller material is carried further.
The larger sediment builds up on the banks of the river over multiple floods
This creates a natural embankment on the bank of the river, meaning that the channel can carry more water.
What is an estuary?
Where the river meets the sea
The river here is tidal
When there is less water, the river deposits silt to form mudflats.
Where is the River Tees?
North England
Source is in the Pennines ~893m asl.
Flows east
Mouth joins the North Sea
Where is the River Parrett?
South west England
Source in hills in Dorset ~179m asl.
Flows through Dorset and Somerset
Mouth meets the Bristol Channel
Factors that have affected the River Tees
Geology: contributed to the formation of the High Force waterfall. Its source is in an area of limestone, which is soluble and has contributed to the formation of a gentle v-shaped valley. Downstream, the geology changes to be more resistant Whin Sill which is far more resistant and the valley becomes more vertical.
Topography: Source in Pennines, upland area, a lot of rainfall as the moorland is easily saturated
Humans: In 1810, Mondal loop cut off to straighten river for ships. Waste from ships narrowed river around Teesside.
Sheltered bays
Shallow water
Groynes on the beach.
Sea attacks a section of coast with alternating bands of soft rock.
This leaves a section of land jutting out into the sea called a headland.
The areas where softer rock has eroded away are called bays.
In a straight river, riffles (shallow with deposition) and channel pools (deep with erosion) will form.
This results in areas of slow and fast water movement.
Flood management strategies
Hard engineering
Soft engineering
Forecasting and education
Planning and building design
