Welcome to your study notes for Section 1.3 of the Edexcel GCSE Geography (1GA0) specification. This section is part of the physical geography topic The changing landscapes of the UK.

What you'll learn

• The physical processes of weathering, mass movement, erosion, transport, and deposition that shape river environments.
• How a river's profile and channel change from source to mouth, using the River Tees as our UK located example.
• How distinctive erosional and depositional landforms develop.
• How human activities affect rivers, and how we manage the physical and human causes of flooding.

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1. Physical Processes Shaping River Landscapes

Rivers do not exist in a vacuum; they are dynamic systems shaped by five key physical processes that wear down, move, and deposit material along their course.

Weathering and Mass Movement

Before sediment even enters a river channel, physical processes on the surrounding valley slopes prepare and deliver material to the water.

• Mechanical (physical) weathering: The most common type in the UK is freeze-thaw weathering. Water enters cracks in a rock, freezes, and expands by about 9% in volume. This puts pressure on the rock. When it melts, more water enters the deeper crack. Repeated freezing and thawing eventually shatters the rock.
• Chemical weathering: Acidic rainwater (caused by dissolved carbon dioxide) reacts with minerals in rocks like limestone, dissolving them over time.
• Biological weathering: Plant roots grow into cracks and split rocks apart, or burrowing animals weaken valley slopes.

When weathering weakens the valley slopes, gravity pulls the loose material down towards the river channel. This is called mass movement.

• Sliding (landslides): Blocks of rock slide rapidly down a flat, steep slope along a slide plane.
• Slumping: Saturated soil and weak rock slide downhill along a curved slip plane, creating a stepped slope.

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River Erosion

As water flows, it exerts energy on the river bed and banks, wearing them away.

• Hydraulic action: The sheer force of the moving water forces air into cracks in the river bed and banks. The trapped air is compressed, expanding explosively when the pressure is released, shattering the rock.
• Abrasion: The river's load (pebbles and stones) scrapes and grinds against the bed and banks, wearing them away like sandpaper.
• Attrition: Rocks and pebbles carried by the river knock against each other, breaking into smaller, rounder, and smoother pieces.
• Solution (corrosion): Soluble minerals (like calcium carbonate in limestone) are dissolved in the slightly acidic river water and carried away.

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River Transport

Once material is eroded or delivered to the channel by mass movement, the river transports it downstream.

• Traction: Large, heavy boulders are rolled along the river bed. This requires very high energy.
• Saltation: Small pebbles and stones bounce along the river bed in a leapfrog motion.
• Suspension: Fine, light material (like silt and clay) is carried along within the body of the water, making the river look cloudy or muddy.
• Solution: Dissolved minerals are carried invisibly in the water.

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River Deposition

When a river loses energy, it can no longer transport its load, so it drops it.

A river drops its heaviest load (large boulders) first because they require the most energy to move. The lightest sediment (fine silt) is transported the furthest and deposited last, often near the river's mouth.

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Climate and Weather Influences

The UK's weather and climate strongly affect these processes:

• Short-term storms: Intense rain storms cause rapid surface runoff, rapidly increasing a river's volume of water (discharge). This raises the river's velocity, triggering high rates of hydraulic action and abrasion, and allowing the river to transport much larger sediment.
• Droughts: Extended dry periods reduce water levels, slowing velocity and causing widespread deposition.
• Seasonal climate: UK winters increase freeze-thaw weathering on valley slopes, supplying more loose rock to the river system.

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2. Long Profiles, Cross Profiles, and the River Tees

As a river flows downstream from its upland source to its lowland mouth, its landscape changes dramatically.

The Three Courses of a River

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Located Example: The River Tees

To meet the Edexcel requirement for a named UK river landscape, we study the River Tees in northeast England.

• Location: The Tees flows 137 km from its upland source at Cross Fell (Pennines) eastward to its lowland mouth at Teesmouth near Middlesbrough, where it enters the North Sea.
• Upper Course: It starts about 600m above sea level. Here, geology plays a huge role. It runs over hard, resistant igneous rock called Whin Sill. This results in vertical erosion, forming a steep-sided V-shaped valley and the famous High Force Waterfall (the UK's largest waterfall by volume, dropping 21m).
• Middle Course: As the gradient decreases, lateral (sideways) erosion dominates. The river meanders across a wider valley floor near Barnard Castle.
• Lower Course: The river flows through a flat, wide floodplain. It has large meanders, levees, and a wide estuary surrounded by heavy industry at Teesport.

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3. River Landforms

River landforms are categorised by the processes that create them: erosion, deposition, or a mixture of both.

Erosional Landforms

Interlocking Spurs

In the upper course, the river has low discharge and vertical erosion dominates. The river does not have the energy to erode laterally through hillsides, so it winds its way around fingers of harder rock that jut into the valley. These fingers are called interlocking spurs.

Waterfalls and Gorges

When a river flows over an area of alternating hard (resistant) rock and soft (less resistant) rock, a waterfall forms.

1. The river erodes the soft rock faster than the hard rock, creating a step in the river bed.
2. Water rushing over the step hydraulic-actions and abrades the soft rock underneath, creating a plunge pool.
3. Over time, the hard cap-rock is left overhanging because its support below has been eroded away.
4. Eventually, gravity causes the overhanging hard rock to collapse into the plunge pool.
5. This process repeats over thousands of years, causing the waterfall to retreat upstream, leaving behind a steep-sided valley called a gorge.

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Depositional Landforms

Floodplains and Levees

• Floodplain: A wide, flat area of land on either side of a river in its middle and lower courses. During a flood, the river overflows its banks. Because water spreading over the land is shallow and meets friction from grass and soil, its velocity drops instantly. It deposits its finest sediment (alluvium), which builds up over successive floods to form a fertile floodplain.
• Levees: Naturally raised banks along the edges of the river channel. When the river floods, the heaviest, coarsest sediment is deposited first, right next to the channel edge. Over time, this coarse material builds up into high ridges.

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Erosional and Depositional Landforms

Meanders and Oxbow Lakes

Meanders are sweeping bends in a river, created by a combination of lateral erosion and deposition.

• Outer Bend (Erosion): Water flows fastest on the outer bend of a meander loop because it has the most momentum. This high velocity causes lateral erosion (abrasion and hydraulic action), cutting into the bank and forming a steep river cliff.
• Inner Bend (Deposition): On the inside of the bend, water is slow-moving. Because velocity is low, the river deposits sand and gravel, forming a gently sloping beach called a slip-off slope (or point bar).
• Oxbow Lakes: Over time, lateral erosion narrows the neck of the meander loop. During a period of high discharge (a flood), the river takes the straightest, fastest route, cutting directly through the narrow neck. Deposition eventually seals off the old meander loop, leaving a crescent-shaped oxbow lake.

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4. Flooding and Human Interventions

Flooding occurs when a river's discharge exceeds the capacity of its channel, causing water to overflow onto the surrounding land.

Causes of Flooding

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Storm Hydrographs

Geographers use storm hydrographs to show how a river's discharge responds to a specific rainfall event.

Let's look at a practical example of how to calculate a river's lag time using data from a hydrograph.

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Managing Flooding: Hard vs. Soft Engineering

Flood defences protect settlements and infrastructure from the devastating impacts of flooding.

Hard Engineering

This involves building artificial, heavy structures to control the flow of the river.

• Dams and Reservoirs: Huge concrete walls built across a river valley to trap water in a reservoir.
  • Advantage: Very effective at regulating water flow; can generate renewable hydroelectric power (HEP).
  • Disadvantage: Extremely expensive; floods massive areas upstream, displacing communities and destroying habitats.
• Channelisation: Straightening or deepening the river channel so water flows away faster.
  • Advantage: Protects the immediate urban area by removing water quickly.
  • Disadvantage: Speeds up the water, increasing the risk of severe flooding further downstream.

Soft Engineering

This uses natural processes and working with nature to reduce the risk of flooding.

• Flood Plain Zoning: Restricting what can be built on different parts of the floodplain. Low-value land (like parks or pasture) is placed near the river, while high-value buildings (homes, hospitals) are built far away.
  • Advantage: Inexpensive and preserves natural habitats without disrupting the river.
  • Disadvantage: Limits where towns can grow; cannot protect existing buildings already built on the floodplain.
• Washlands: Areas on the floodplain deliberately allowed to flood safely during high discharge.
  • Advantage: Absorbs excess water naturally and creates wetland habitats.
  • Disadvantage: Farmland within the washlands cannot be used for crops during flood season.

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