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Unlock This CourseRivers are like nature's conveyor belts, constantly moving materials downstream. Transportation is one of the key processes that shapes our landscape, working alongside erosion and deposition to create the river valleys we see today. Understanding how rivers transport material helps explain why some rivers are muddy brown whilst others run crystal clear.
River transportation is the process by which rivers pick up and carry sediment, rocks and dissolved materials from their source to their mouth. This process is crucial for understanding how rivers shape the landscape and create various landforms along their journey.
Key Definitions:
Transportation connects the entire river system. Material eroded from mountains eventually reaches the sea, creating deltas and coastal plains. Without transportation, rivers would simply be channels of flowing water with no power to shape the landscape.
Rivers transport material in four distinct ways, each suited to different sizes and types of particles. The method used depends on the river's energy, velocity and the size of the material being moved.
This is the invisible transportation method where minerals and chemicals are dissolved directly into the water. You can't see this happening, but it's constantly occurring as slightly acidic river water chemically breaks down rocks like limestone and chalk.
Calcium carbonate from limestone, salt from rock salt deposits and other soluble minerals. This creates the 'hardness' in water.
Very little energy needed - happens even in slow-moving water. Chemical weathering does most of the work.
The River Thames carries dissolved limestone from the Cotswolds, making London's water naturally 'hard'.
Fine particles like clay, silt and small sand grains are carried within the water column, giving many rivers their muddy brown colour. These particles are light enough to be supported by the water's turbulence.
Clay particles, fine silt and small sand grains. These create the cloudy, muddy appearance in many rivers.
Most effective during floods when turbulence is high. Calm water allows particles to settle.
Rivers carrying lots of suspended load look brown or muddy. Clear rivers have little suspended material.
The River Severn, Britain's longest river, demonstrates suspension transport perfectly. During winter floods, the river turns chocolate brown as it carries millions of tonnes of suspended sediment from Welsh hills towards the Bristol Channel. In summer, when flow is lower, the water runs much clearer as particles settle out.
Medium-sized particles like sand and small pebbles are too heavy to stay suspended but too light to roll along the bottom. Instead, they bounce along the riverbed in a series of hops and jumps.
Particles are picked up by fast-flowing water, carried a short distance, then dropped back down. The impact can dislodge other particles, creating a chain reaction of bouncing sediment.
The heaviest materials - large pebbles, cobbles and boulders - are rolled, dragged, or slid along the riverbed. This requires the most energy and only happens during high-flow conditions.
Large pebbles, cobbles and even boulders during extreme floods. Size depends on river energy.
Massive amounts of energy required. Only happens during floods or in very steep, fast-flowing sections.
You can actually hear traction happening - rocks grinding and bumping along the riverbed during floods.
Several factors determine how much material a river can transport and which method it uses. Understanding these factors helps explain why rivers behave differently in various locations and seasons.
Velocity is the most important factor. As water moves faster, it gains energy exponentially - doubling the velocity gives four times the energy. This energy determines both competence (largest particle size) and capacity (total volume).
Fast-flowing water in mountain streams can move boulders, whilst slow lowland rivers can barely transport sand. The relationship isn't linear - small increases in speed create huge increases in transport power.
Smaller, rounder particles are easier to transport than large, angular ones. This is why rivers naturally sort their load, with fine material travelling furthest and coarse material staying closer to the source.
More water means more transport capacity. During floods, rivers can carry hundreds of times more material than during dry periods. This is why most landscape change happens during extreme weather events.
The River Tees in North Yorkshire shows all transport types clearly. In its upper course near High Force waterfall, traction moves large boulders during floods. In the middle course, saltation bounces pebbles along the bed. By the time it reaches Middlesbrough, the river mainly transports fine suspended sediment and dissolved minerals, creating the muddy waters of the Tees estuary.
Transportation changes dramatically as rivers flow from source to mouth. Understanding these changes helps explain why different landforms develop in different parts of the river system.
In steep mountain areas, rivers have high energy but low volume. Transportation is mainly through traction and saltation, moving large, angular rocks short distances. The load is coarse but the total amount is relatively small.
As rivers gain volume and gradient decreases, transportation becomes more efficient. All four types occur, but saltation and suspension dominate. Particles become smaller and more rounded through attrition.
Large, slow-moving rivers rely heavily on suspension and solution. The load is fine but the total volume is enormous. These rivers can transport millions of tonnes of sediment annually.
Surprisingly, lower course rivers often transport more material than upper course rivers, despite moving more slowly. This is because they have much greater volume and their fine load is easier to carry.
Human activities significantly affect river transportation processes. Dams, channelisation and land use changes all alter natural transport patterns, sometimes with unexpected consequences.
Dams trap sediment, reducing downstream transport capacity. This can cause riverbed erosion below dams and sediment starvation in deltas. The Aswan High Dam on the River Nile demonstrates this effect clearly.
Urban development increases surface runoff, leading to higher peak flows that can dramatically increase transport capacity during storms. This often results in increased erosion and sedimentation problems downstream.