PL- Rivers Flashcards
How does a river change from source to mouth?
Upper- shallow, thin, large jagged rocks
Lower- deep, wide, small rounded rocks
What are the characteristics of a meander?
Curved Shape: Meanders have a sinuous, snake-like shape, characterized by a series of alternating bends.
Erosion and Deposition: The outer bank (cut bank) of a meander experiences erosion due to faster-flowing water, while the inner bank (slip-off slope) sees sediment deposition due to slower-flowing water.
Point Bars: The inner side of the meander curve forms point bars, which are deposits of sand and gravel.
River Cliffs: The outer side of the meander curve forms steep river cliffs due to continuous erosion.
How does an oxbow lake form?
Meander Formation: A river develops large bends or meanders due to the differential flow of water, which erodes the outer banks (cut banks) and deposits sediment on the inner banks (point bars).
Neck Narrowing: Over time, the meanders become more pronounced, and the neck of the meander (the narrow strip of land between the bends) becomes increasingly narrow due to continued erosion.
Cut-off: During a flood or high flow event, the river may break through the narrow neck of the meander, creating a new, straighter channel for the river to flow through. This effectively cuts off the meander loop from the main river.
Deposition: Sediment is deposited at the entrance and exit of the cut-off meander loop, sealing it off from the main river channel and isolating the loop.
Oxbow Lake Formation: The isolated meander loop, now cut off from the main flow of the river, becomes an oxbow lake. Over time, the oxbow lake may fill with sediment and vegetation, eventually becoming a meander scar.
What affects a hydrograph?
- rock type
- land type
- relief of river
- soil moisture
What are 4 human factors that affect flooding?
Urbanisation: The development of urban areas often involves replacing natural landscapes with impervious surfaces like roads and buildings. This reduces the land’s ability to absorb water, leading to increased surface runoff and higher chances of flooding during heavy rainfall.
Deforestation: The removal of trees and vegetation reduces the land’s capacity to absorb and hold water. Without trees, the soil is less stable and more prone to erosion, leading to increased runoff and a higher risk of flooding.
Agricultural Practices: Certain agricultural activities, such as overgrazing and improper plowing, can compact the soil, reducing its ability to absorb water. Additionally, drainage systems used in agriculture can direct water quickly into rivers, increasing the risk of floods.
Climate Change: Human-induced climate change leads to more extreme weather patterns, including heavier and more frequent rainfall events. This increases the likelihood of flooding as existing drainage systems and natural waterways may be unable to cope with the higher volumes of water.
What are 4 physical factors that affect flooding?
Heavy, Prolonged Rainfall: Intense and extended periods of rainfall can quickly saturate the soil, leading to surface runoff and increasing the likelihood of rivers and streams overflowing their banks.
Steep Slopes: In areas with steep slopes, rainwater flows more quickly towards rivers and streams, increasing the volume and speed of the water, which can cause rapid flooding downstream.
Snowmelt: Rapid melting of snow due to a sudden increase in temperature can release large amounts of water into rivers and streams, overwhelming their capacity and causing floods.
Soil Permeability: The ability of soil to absorb water affects flooding. Areas with low-permeability soils, such as clay, do not absorb water well, leading to higher runoff and increased flood risk.
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What are the four types of river erosion?
- Hydraulic action – Water forces air into cracks.
- Abrasion – Sediment scrapes the riverbed.
- Attrition – Rocks collide and break.
- Solution – Acidic water dissolves rocks.
What are the four types of transportation in rivers?
- Traction – Large rocks roll along the riverbed.
- Saltation – Pebbles bounce along the riverbed.
- Suspension – Small particles carried in water.
- Solution – Dissolved materials carried in water.
What landforms are found in the upper course of a river?
- Waterfalls & gorges – Formed by resistant rock.
- Interlocking spurs – River weaves around hard rock.
How do waterfalls form?
- Hard rock over soft rock.
- Soft rock erodes, forming a step.
- Overhang collapses, waterfall retreats.
- Leaves a gorge.
What landforms are found in the middle course?
- Meanders – Bends in a river due to erosion and deposition.
- Ox-bow lakes – Cut-off meanders after deposition seals the loop.
What landforms are found in the lower course?
- Levees – Raised river banks formed by repeated flooding.
- Floodplains – Wide, flat areas prone to flooding.
- Estuaries – Mudflats and salt marshes formed by deposition.
What factors affect flood risk?
- Physical: Heavy rain, steep slopes, impermeable rock.
- Human: Urbanisation, deforestation, farming.
What are the types of flood management?
- Hard engineering: Dams, embankments, channel straightening.
- Soft engineering: Afforestation, flood warnings, river restoration.
Case Study: Flood Management - River Tees
Why?: Reduce flooding, protect towns.
What?: Dams, embankments, flood relief channels.
Effects: Controlled floods but expensive.
Case Study: Flood Relief - Jubilee River (Thames)
Why?: Reduce flood risk in Maidenhead & Eton.
What?: 12km artificial channel built.
Issues: Expensive (£110m), caused flooding downstream.
