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examBoard: Cambridge
examType: IGCSE
lessonTitle: Flooding Physical Impacts
Flooding is one of the most common and destructive natural hazards worldwide. When rivers, lakes, or oceans overflow, the water can dramatically change the physical landscape in both the short and long term. These physical impacts are separate from the human and economic costs, focusing instead on how flooding alters the natural environment.
Key Definitions:
Fluvial (river) flooding: Occurs when rivers burst their banks due to excessive rainfall, snowmelt, or dam failure.
Pluvial (surface) flooding: Happens when heavy rainfall overwhelms drainage systems, creating surface runoff.
Coastal flooding: Results from storm surges, tsunamis, or high tides combined with stormy conditions.
Flash flooding: Rapid flooding that occurs within 6 hours of heavy rainfall, often in steep catchments.
Flood magnitude: The size and power of the flood determines its erosive potential.
Duration: Longer floods typically cause more extensive physical changes.
Velocity: Faster-moving floodwaters have greater erosive power.
Sediment load: The amount and type of material carried by floodwaters affects deposition patterns.
Landscape characteristics: Slope, soil type and vegetation cover influence flood impacts.
Flooding dramatically accelerates erosion processes, reshaping landscapes in hours or days that might normally take decades. The increased volume and velocity of water during floods gives it tremendous erosive power.
Floodwaters erode the landscape through four main processes:
The sheer force of fast-moving water against river banks and beds can dislodge material. Air becomes trapped in cracks and crevices, creating pressure that can break apart rocks and soil. During floods, this process intensifies dramatically.
Sediment carried by floodwaters acts like sandpaper, scraping and wearing away at channel beds and banks. The higher sediment load during floods makes this process more destructive, scouring out new channels and undercutting banks.
Attrition occurs as rocks and debris in floodwaters collide and break down into smaller pieces. Solution involves the dissolving of soluble rocks like limestone. Both processes are accelerated during flood events due to increased turbulence.
Floods can dramatically reshape landscapes through their erosive power. Some of the most significant changes include:
Storm Desmond in December 2015 caused severe flooding in Cumbria, with the River Eden experiencing its highest ever recorded flow of 1,700 cumecs. The flood physically reshaped the landscape by:
The physical changes were so significant that new flood management strategies had to be developed based on the altered river system.
As floodwaters recede and lose energy, they deposit the material they've been carrying. This deposition can create new landforms and alter existing ones.
Floodplain deposits: Layers of fine silt and clay that build up over time, creating fertile agricultural land.
Natural levees: Raised banks alongside rivers formed when coarser material is deposited close to the channel during floods.
Alluvial fans: Fan-shaped deposits that form where rivers emerge from upland areas onto flatter land.
Braided channels: Multiple, interweaving channels separated by small, temporary islands formed by sediment deposition.
Floodwaters sort material by size and weight:
Largest material: Deposited first, often close to the main channel.
Medium-sized material: Carried further onto the floodplain.
Finest material (silt/clay): Can be carried great distances before being deposited as floodwaters recede.
This sorting creates distinct layers in floodplain soils that scientists can study to understand flood history.
Flooding has significant effects on soil properties and plant communities, which can persist long after the floodwaters have receded.
In spring 2011, the Mississippi River experienced its most significant flooding since 1927. The physical impacts included:
Scientists continue to study these changes to better understand how large river systems respond to major flood events.
While individual floods cause immediate physical changes, repeated flooding over time shapes entire landscapes and ecosystems.
Flooding is a powerful force that reshapes landscapes through erosion and deposition. The physical impacts include channel changes, soil alteration, vegetation disruption and the formation of distinctive landforms. Understanding these physical processes is crucial for predicting how landscapes will respond to future flood events, especially as climate change alters rainfall patterns worldwide.
The physical impacts of flooding are not always negative from an environmental perspective. Many ecosystems depend on regular flooding cycles and the sediment deposited by floods can renew soil fertility. However, extreme flood events can cause dramatic and sometimes irreversible changes to landscapes, particularly when they exceed historical norms.
By studying the physical impacts of past floods, environmental scientists can better predict how future events might affect landscapes and develop more effective strategies for flood management that work with natural processes rather than against them.
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