Curriculum Portal

neurologyYou need to know

• The hydrological cycle continuously moves water between the atmosphere and Earth's surface through evaporation, transpiration from plants, condensation into cloud droplets, and precipitation as rain, snow, sleet or hail.
• A river flows downhill through a channel from its source to its mouth, where it enters a sea, lake or another river; a tributary joins a larger river at a confluence.
• A drainage basin is the area drained by a river and its tributaries, bounded by a watershed of higher land, with water reaching channels through surface runoff, throughflow in soil and groundwater flow after infiltration.
• Glaciers are slowly moving masses of ice that covered large parts of the UK during past glacial periods, creating U-shaped valleys through plucking of loosened rock and abrasion by embedded debris, and depositing rock and sediment as moraines.
• From source to mouth, river gradient generally decreases while channel width, depth, discharge and average velocity generally increase; discharge is the volume of water passing a point each second.
• The upper course typically has steep gradients, narrow valleys and mainly vertical erosion, the middle course has wider valleys and meanders, and the lower course has broad floodplains and extensive deposition.
• River erosion involves hydraulic action, where water pressure and compressed air loosen rock; abrasion, where sediment scrapes the bed and banks; attrition, where transported rocks collide and become smaller and rounder; and solution, where soluble rock dissolves.
• A waterfall can form where resistant rock overlies less resistant rock, which erodes faster to create a plunge pool and undercut the overhang; repeated collapse and upstream retreat leave a steep-sided gorge.
• Rivers transport material by traction, which rolls large particles along the bed; saltation, which bounces smaller particles along the bed; suspension, which carries fine particles within the water; and solution, which carries dissolved substances.
• Deposition occurs when a river can no longer transport its load, often because its velocity falls, with larger particles generally settling first and deltas forming at river mouths where sediment accumulates faster than it is removed.
• At a meander, faster flow on the outer bend causes erosion and forms a river cliff, while slower flow on the inner bend deposits sediment to form a slip-off slope.
• An ox-bow lake forms when erosion narrows a meander neck, the river cuts through it, often during a flood, and deposition seals the ends of the abandoned bend.
• Floodplains develop through sideways migration of meanders and deposition of sediment during floods, while natural levees build beside the channel as floodwater slows and deposits its coarser sediment first.
• River flooding occurs when water exceeds channel capacity and spills onto surrounding land, with prolonged or intense rainfall, snowmelt, saturated ground, impermeable rock and steep slopes increasing or accelerating water delivery to the channel.
• Urbanisation increases runoff through impermeable surfaces and drains, deforestation reduces interception and water uptake, and building on floodplains exposes more people and property to flooding and can reduce floodwater storage.
• Climate change is increasing the likelihood and intensity of heavy rainfall events in the UK, which can increase flood risk depending on drainage-basin conditions.
• Hard engineering uses built structures or channel alterations to manage rivers, including dams that store water, embankments and flood walls that contain higher flows, and channelisation that moves water downstream more quickly.
• Soft engineering reduces flood risk through measures such as afforestation to intercept rainfall, washlands to store floodwater, floodplain zoning to restrict development, and flood warnings to help people prepare.
• Hard engineering can protect settlements effectively but is often expensive and may damage habitats or transfer risk downstream, while soft engineering can support habitats and long-term sustainability but may require extensive land and cannot prevent all flood damage.
• The Somerset Levels, a low-lying area drained by rivers including the Parrett and Tone, flooded in winter 2013–14 after prolonged rainfall, causing evacuations, flooded homes, disrupted roads and submerged farmland, with subsequent management including dredging, improved pumping and raised embankments to reduce rather than eliminate future risk.

• Construct annotated diagrams of the hydrological cycle and a drainage basin, using arrows to show water transfers and accurately labelling infiltration, surface runoff, throughflow, groundwater flow, tributaries and the watershed.
• Interpret river long profiles and channel cross-sections to describe changes in height, gradient, width and depth, linking these changes to discharge and dominant processes from source to mouth.
• Explain how glacial plucking, abrasion and deposition shaped UK landscapes, identifying U-shaped valleys and moraines in photographs or diagrams.
• Distinguish erosion, transportation and deposition in river scenarios, identifying the relevant process from evidence about sediment movement, particle size and flow conditions.
• Sequence and annotate the formation of waterfalls, gorges, meanders and ox-bow lakes, linking each stage to erosion, deposition or collapse.
• Explain the formation of floodplains and natural levees using lateral erosion, repeated flooding, falling velocity and the order in which sediment is deposited.
• Explain how physical and human factors affect flood risk by tracing their effects on interception, infiltration, runoff, river discharge or exposure on floodplains.
• Compare hard and soft engineering strategies, explaining how each selected measure changes water storage, river flow or people's exposure to flooding.
• Evaluate flood-management options against effectiveness, cost, maintenance, environmental impact and downstream effects, reaching a justified judgement about sustainability.
• Use evidence from the Somerset Levels floods of 2013–14 to explain causes, distinguish social, economic and environmental impacts, and assess the benefits and limitations of management responses.