What you'll learn
This revision guide covers the physical processes that shape coastal and river landscapes, focusing on the mechanisms of erosion, transportation, and deposition. You will learn to identify and explain how distinctive landforms develop through these processes, and understand the techniques used to investigate them in the field. This content is essential for Paper 1 and fieldwork components of your Pearson Edexcel International IGCSE Geography examination.
Key terms and definitions
Hydraulic action — erosion caused when water is forced into cracks in rocks, compressing air which breaks the rock apart when pressure is released
Attrition — the process by which transported particles collide and break into smaller, rounder fragments
Longshore drift — the zigzag movement of sediment along a coastline, driven by waves approaching at an angle to the shore
Traction — the rolling of large sediment particles along a river or sea bed by water flow
Deposition — the process by which transported sediment is laid down when the energy of water movement decreases
Saltation — the bouncing movement of medium-sized particles along a river or sea bed
Weathering — the breakdown of rock in situ (in place) by mechanical, chemical or biological processes
Load — the total amount of sediment carried by a river or waves at any given time
Core concepts
Coastal erosion processes
Coasts are shaped by four main erosional processes working together. Hydraulic action occurs when waves crash against cliffs, forcing water into cracks at high pressure. This compresses air in the cracks; when the wave retreats, the air expands explosively, widening cracks and breaking off rock fragments. This process is most effective on coasts with jointed rocks like limestone or chalk.
Abrasion (also called corrasion) happens when waves pick up sediment and hurl it against the cliff face, acting like sandpaper. This is the most powerful erosive force on coasts, particularly effective during storms when waves have greater energy and can transport larger particles.
Attrition rounds and reduces the size of sediment as particles collide during transport. Beach pebbles become progressively smaller and rounder moving along a coastline, eventually forming sand. Solution (or corrosion) dissolves soluble rocks like limestone and chalk through weak acids in seawater, though this process is slower than mechanical erosion.
Wave energy determines erosion rates. Destructive waves (high, frequent waves with strong backwash) erode coastlines rapidly. Constructive waves (low, gentle waves with strong swash) deposit more material than they remove.
River erosion processes
Rivers erode through the same four processes as coasts, but their relative importance varies with channel characteristics. In the upper course, vertical erosion dominates as the river cuts downward into the landscape. Hydraulic action and abrasion are most effective here due to steep gradients and large, angular bedload.
Vertical erosion deepens the river valley through the same hydraulic action and abrasion processes described above. Potholes form where abrasion is concentrated on the river bed, creating circular depressions as sediment swirls in turbulent flow.
In the middle and lower courses, lateral erosion widens the valley as the river meanders. The fastest flow occurs on the outside of meander bends (the outer bank), where erosion concentrates. The river undercuts the bank through hydraulic action and abrasion, forming a river cliff.
Solution is particularly important in rivers flowing over limestone or chalk bedrock, where dissolved calcium carbonate is carried in solution even when the water appears clear.
Transportation processes
Both rivers and coasts transport sediment through four mechanisms. The process used depends on particle size and water velocity.
Traction moves the largest particles (boulders and cobbles) by rolling them along the bed. This requires high energy and occurs during floods in rivers or storms on coasts.
Saltation transports smaller pebbles and coarse sand by bouncing them along the bed in a series of hops. Medium-sized particles are too heavy to remain suspended but light enough to be lifted temporarily by turbulent flow.
Suspension carries fine particles (silt and clay) within the water column. These particles give rivers and coastal waters a brown or cloudy appearance. Suspension can transport material over vast distances.
Solution transports dissolved minerals invisibly. Rivers draining limestone areas may carry significant dissolved load despite appearing clear.
In coastal environments, longshore drift is the primary transport mechanism. Waves approach the shore at an angle determined by prevailing wind direction. The swash (wave movement up the beach) carries sediment at this angle. Backwash (return flow under gravity) pulls material straight down the slope. This creates a zigzag transport pattern along the coastline. On UK coasts, the prevailing southwest winds typically drive longshore drift from west to east.
Deposition and coastal landforms
Deposition occurs when water velocity decreases and can no longer transport its load. In coastal environments, this creates distinctive features.
Beaches form when constructive waves deposit material. Shingle beaches (with larger particles) have steep gradients because large particles lose energy rapidly. Sand beaches have gentler gradients as smaller particles are carried further up the shore before deposition.
Spits develop where coastlines change direction or where a river mouth disrupts longshore drift. Sediment is deposited in open water, extending from the coast. The spit grows in the direction of longshore drift and often develops a curved (recurved) end where wave refraction or secondary winds push material back toward the shore. Orford Ness in Suffolk, England, extends 15 kilometers along the coast, demonstrating long-term spit development.
Bars form when spits grow completely across a bay or river mouth, creating a lagoon behind. Slapton Ley in Devon is enclosed by a bar connecting previously separate headlands.
Tombolos are sediment deposits connecting an island to the mainland, formed by deposition in the wave shadow behind the island. Chesil Beach connects the Isle of Portland to the Dorset coast.
Deposition and river landforms
Rivers deposit sediment when velocity decreases. This occurs when gradient reduces, discharge falls, or the river enters standing water.
Floodplains are flat areas beside rivers in the middle and lower courses, built up by sediment deposited during floods. When rivers overflow, velocity decreases rapidly across the floodplain and sediment settles. Repeated flooding over centuries creates extensive flat areas. The levees (raised banks) beside river channels form through preferential deposition of coarser material closest to the channel during floods.
Meanders form in the middle and lower courses where lateral erosion and deposition work together. Fast flow on the outer bend causes erosion, while slow flow on the inner bend causes deposition, creating a point bar (slip-off slope). Over time, meanders migrate downstream and across the floodplain.
Ox-bow lakes form when meanders become increasingly sinuous until the narrow neck between bends is breached (usually during floods). The river takes the shorter route, and deposition seals off the old meander loop, leaving a curved lake.
Deltas form where rivers deposit sediment when entering the sea or lakes. Velocity decreases as the river enters standing water, depositing the heaviest particles first. The river divides into multiple channels (distributaries) to navigate around deposited material. The Nile Delta and Mississippi Delta are classic examples, though delta formation requires sediment deposition to exceed coastal erosion and removal.
Fieldwork investigation techniques
Paper 2 requires understanding of fieldwork methods used to investigate coastal and river processes.
Beach profile surveys measure beach gradient and shape using ranging poles and clinometers. Measurements are taken at regular intervals from the sea to the back of the beach, recording distance and angle. This data reveals beach zones and helps identify areas of deposition versus erosion.
Sediment analysis investigates transported material. Particle size is measured using calipers or size charts, with measurements recorded at multiple sites to show downstream changes. Roundness is assessed using Powers' Scale (angular to well-rounded), demonstrating the effect of attrition during transport.
River velocity measurements use a flow meter or float timing method. Measurements at different points across the channel reveal velocity variations (fastest at the thalweg, slowest near banks and bed due to friction). Multiple cross-sections along the river course show how velocity changes downstream.
Wave frequency counts record the number of waves breaking per minute, distinguishing constructive from destructive waves. Destructive waves typically exceed 10-14 per minute.
Pebble orientation measurements on beaches reveal longshore drift direction, as pebbles align with their long axis parallel to the wave direction.
Data presentation requires appropriate graphs and maps. Beach profiles use line graphs. Sediment size data works well in scatter graphs showing downstream changes. Velocity data can be presented in cross-sectional diagrams or bar charts.
Factors affecting processes and landforms
Multiple factors interact to determine which processes dominate and what landforms develop.
Geology controls erosion rates and cliff profiles. Resistant rocks like granite erode slowly, creating rocky coasts with small beaches. Weaker rocks like clay erode rapidly, creating bays. On rivers, resistant rock creates waterfalls and rapids where hard bands cross the channel.
Climate influences process rates through precipitation (affecting river discharge and erosion) and temperature (affecting weathering rates and freeze-thaw action in both coastal and river environments).
Human activity modifies natural processes. Coastal defences like groynes interrupt longshore drift, causing deposition on the updrift side and increased erosion downdrift. River channelization increases velocity, potentially increasing erosion downstream. Dam construction traps sediment, reducing deposition in deltas and on floodplains.
Vegetation stabilizes banks and beaches, reducing erosion. Tree roots bind riverbanks, while marram grass stabilizes coastal dunes.
Worked examples
Example 1: Explaining spit formation (4 marks)
Question: Explain how a spit forms. (4 marks)
Mark scheme answer:
Longshore drift transports sediment along the coast [1 mark]. Where the coastline changes direction, such as at a river mouth or bay, sediment continues to be deposited in open water [1 mark]. This extends the beach outward from the coast [1 mark]. The spit often develops a curved end due to wave refraction or secondary winds pushing material landward [1 mark].
Examiner note: This answer gains full marks by identifying the transport process (longshore drift), the location (coastline change), the depositional process (continuing deposition), and additional detail (recurved end). Alternative valid points include: reference to constructive waves, formation of a salt marsh in the sheltered area behind the spit, or specific examples.
Example 2: Comparing processes in upper and lower river courses (6 marks)
Question: Compare the processes operating in the upper and lower courses of a river. (6 marks)
Mark scheme answer:
In the upper course, vertical erosion dominates, cutting down into the valley floor, whereas in the lower course, lateral erosion is more significant, widening the valley [2 marks for developed comparison]. The upper course has a large, angular bedload transported mainly by traction due to steep gradients, while the lower course carries a greater proportion of suspended sediment and dissolved load due to attrition reducing particle size [2 marks for developed comparison]. Deposition is rare in the upper course except in sheltered areas behind boulders, but in the lower course, deposition is widespread across floodplains during floods due to decreased velocity [2 marks for developed comparison].
Examiner note: This gains full marks through three developed comparisons using comparative language (whereas, while) and specific detail. Each comparison contrasts both courses rather than describing them separately.
Example 3: Evaluating fieldwork methods (8 marks)
Question: "Beach sediment analysis is more useful than measuring beach profiles for investigating coastal processes." Do you agree? (8 marks)
Mark scheme answer:
Beach sediment analysis provides valuable data on transportation processes [1 mark]. By measuring particle size and roundness at different locations, you can identify the direction of longshore drift and demonstrate attrition effects [1 mark]. For example, if sediment becomes smaller and rounder in an eastward direction, this indicates longshore drift toward the east [1 mark].
However, beach profiles reveal information about erosion and deposition patterns [1 mark]. A steep profile suggests destructive waves and erosion, while a gentle profile indicates constructive waves and deposition [1 mark]. Profile data also shows beach zones such as berms, which indicate high tide marks [1 mark].
The most useful approach combines both methods [1 mark], as sediment data explains the processes while profile data shows their effects on landform development [1 mark].
Examiner note: This gains 8 marks by discussing strengths of both methods with specific examples, using evidence, and reaching a balanced conclusion. Top-level answers require evaluation (weighing up) rather than just description.
Common mistakes and how to avoid them
Confusing erosion processes: Students often mix up hydraulic action (water pressure breaking rock) with abrasion (sediment scraping rock). Remember: hydraulic action uses only water pressure; abrasion requires sediment as a tool. Both processes can occur simultaneously but work differently.
Misunderstanding longshore drift direction: Don't assume longshore drift always moves in one direction. It follows prevailing wind direction, which varies by location. In the UK it's typically southwest to northeast; this differs elsewhere. Always relate drift direction to local wind patterns.
Confusing landforms of erosion and deposition: Caves, arches, stacks, and wave-cut platforms are erosional features. Beaches, spits, bars, and tombolos are depositional. Don't describe a spit as forming through erosion or a stack through deposition.
Vague fieldwork descriptions: Saying "we measured the beach" gains no marks. Specify the method: "we measured beach gradient using ranging poles placed at 10-meter intervals and a clinometer to measure the angle between poles." Include equipment, technique, and data recorded.
Forgetting to explain processes fully: Don't just name a process. If asked to explain erosion, identify the process (e.g., hydraulic action), describe what happens (water forced into cracks under pressure), and state the result (rock breaks apart). Three-stage explanation: process name → mechanism → outcome.
Weak fieldwork evaluations: Don't just list limitations. Explain why they matter and suggest improvements. "Weather affected our results because strong winds made it difficult to measure wave direction accurately; we could improve this by returning on a calmer day or using a digital compass for more precise measurements."
Exam technique for Physical Geographical Investigations: Coastal and River Processes
Command word precision: "Describe" requires you to say what happens without explanation (1 mark per distinct point). "Explain" requires reasons and mechanisms (developed points worth 2 marks). "Compare" demands you show similarities and differences using comparative language. "Evaluate" needs you to weigh up strengths and weaknesses before reaching a judgment.
Fieldwork question structure: For 6-8 mark fieldwork questions, organize answers using: methodology (what you did and why), results (what you found with specific data), analysis (what this shows about processes), and evaluation (limitations and improvements). This mirrors the mark scheme structure.
Linking processes to landforms: When explaining landform formation, always connect processes to outcomes. Don't just describe the landform's appearance. For example: "The waterfall formed because resistant limestone overlies weaker shale. Hydraulic action and abrasion erode the shale faster, undercutting the limestone until it collapses, maintaining the vertical face."
Using located examples effectively: Named examples demonstrate knowledge but must be used purposefully. Don't force them in; use them to illustrate processes or provide evidence. "The spit at Spurn Head, Yorkshire, demonstrates longshore drift's power, extending 5.5 kilometers and requiring regular management due to erosion of the narrow neck connecting it to the mainland."
Quick revision summary
Coastal and river landscapes form through erosion (hydraulic action, abrasion, attrition, solution), transportation (traction, saltation, suspension, solution), and deposition when energy decreases. Coasts develop spits, bars, and beaches through longshore drift and wave action. Rivers create V-shaped valleys, waterfalls, meanders, floodplains, and deltas through changing erosion and deposition patterns downstream. Fieldwork investigates these processes through beach profiles, sediment analysis, velocity measurements, and other quantitative techniques. Geology, climate, and human activity significantly modify natural process rates and landform development.