Rivers: Key Terms

Rivers: Key Terms

Rivers: key terms

Hydrological characteristics

Aquifer – A layer of permeable rock (such as limestone or sandstone) that stores water underground.

Atmosphere – The layer of gases surrounding the Earth, where water is stored as vapour or droplets in clouds.

Channel flow – Water moving within a river or stream.

Condensation – When water vapour cools and turns back into liquid, forming clouds.

Drainage basin – The area of land drained by a river and its tributaries. Also called a catchment area.

Evaporation – When water changes from liquid to gas due to heat from the sun.

Evapotranspiration – The total loss of water from the Earth's surface and from plants into the air.

Groundwater flow – Water movement through underground rocks.

Infiltration – When water soaks from the surface into the soil.

Input – Water entering the drainage basin, mainly as precipitation.

Interception – When rain is caught by leaves and branches before reaching the ground.

Open system – A system with inputs (like rainfall) and outputs (like evaporation), such as a drainage basin.

Output – Water leaving the drainage basin, for example through evaporation or flow into the sea.

Overland flow – Water flowing over the land when it can’t soak into the ground.

Percolation – Water moving from the soil into underlying rocks.

Precipitation – Any form of water (rain, snow, hail, etc.) falling from the sky to the Earth.

Store – A place where water is held for a while, such as in lakes, ice, or underground.

Throughflow – Water flowing sideways through the soil.

Transpiration – When plants release water vapour into the air through their leaves.

Watershed – The boundary that separates two drainage basins.

River characteristics

Abrasion – Erosion caused by the river's load scraping the bed and banks.

Attrition – When rocks and stones in the river hit each other, breaking into smaller, smoother pieces.

Bradshaw model – A diagram that shows how river features like velocity and discharge change from source to mouth.

Cross profile – A slice across the river channel, showing its shape at different stages.

Deposition – When a river loses energy and drops the material it was carrying.

Discharge – The amount of water flowing in a river, usually measured in cubic metres per second.

Gradient – The slope or steepness of the river’s course.

Hydraulic action – The force of the water breaking rock particles away from the riverbanks and bed.

Hydraulic radius – The efficiency of a river channel, calculated by dividing the cross-sectional area by the wetted perimeter.

Lateral erosion – Erosion of the river banks, widening the river.

Load – The material carried by the river, such as rocks, gravel, and silt.

Long profile – A side view showing how a river’s slope changes from its source to its mouth.

Saltation – When small pebbles are bounced along the riverbed.

Solution (corrosion) – When minerals in rocks are dissolved by slightly acidic water.

Suspension – Fine material carried within the water.

Traction – Large particles rolled along the riverbed.

Velocity – The speed of the river flow.

Vertical erosion – Downward erosion that deepens the river channel.

Wetted perimeter – The total length of riverbed and banks in contact with the water.

River landforms

Alluvium – Fine material such as silt and sand deposited by a river.

Delta – A landform created at the mouth of a river, where sediment is deposited faster than it can be removed, forming land.

Distributaries – Small branches of a river that form in a delta and spread out into the sea.

Estuary – The wide mouth of a river where it meets the sea and saltwater mixes with freshwater.

Floodplain – Flat land next to a river that floods when the river overflows.

Gorge – A steep-sided valley left behind as a waterfall retreats upstream.

Interlocking spurs – Ridges of land around which a river winds in the upper course.

Levee – A natural raised bank formed by deposition during floods.

Meander – A bend or curve in a river, common in its middle and lower courses.

Oxbow lake – A curved lake formed when a meander is cut off from the main river.

Pothole – A small, circular hole in the riverbed caused by abrasion from swirling pebbles.

River cliff – A steep bank on the outside of a meander formed by erosion.

Slip-off slope – A gentle slope on the inside of a meander bend where sediment is deposited.

Source – The beginning of a river, often in high ground like a spring or glacier.

Thalweg – The line of fastest flow in a river, usually found on the outside of bends.

V-shaped valley – A steep valley formed by vertical erosion in the upper course.

Waterfall – A drop in the river's course where water flows over a vertical or near-vertical slope.

River hazards and opportunities

Deforestation – The removal of trees, which reduces interception and increases surface runoff, making flooding and erosion more likely.

Erosion – The wearing away of riverbanks and land, often increased by floods and fast-flowing water.

Flooding – When river water spills over its banks and spreads across the land, usually caused by heavy rain or melting snow.

Hazard – A danger or risk, such as flooding or riverbank erosion.

Opportunity – A benefit of living near rivers, such as fertile soil, easy transport, water supply, and tourism.

Precipitation – Rain, snow, sleet, or hail that can lead to increased river discharge and flooding.

Silt – Fine soil carried and deposited by rivers, often rich in nutrients and good for farming.

River flooding

Afforestation – Planting trees to increase interception and reduce the risk of flooding.

Catchment management plan – A strategy that looks at how to manage the land and water in a river basin to reduce flood risk.

Contour ploughing – Farming technique where ploughing is done across the slope, not down it, to slow runoff.

Dams and reservoirs – Structures built to hold back river water and control the amount flowing downstream.

Deforestation – Cutting down trees, which reduces interception and increases overland flow, making floods more likely.

Drainage basin – The area of land where all rainwater drains into the same river.

Embankment/levee – Raised riverbanks built to contain water and prevent flooding.

Floodplain zoning – A method of planning land use around rivers to minimise damage by restricting building in high-risk areas.

Hard engineering – Building physical structures to manage rivers and reduce flooding (e.g., dams, levees).

River restoration – Returning a river to its natural state to help it manage flooding more sustainably.

Soft engineering – Flood management that works with nature, such as planting trees or using wetlands.

Spillway – A secondary channel that carries excess water during floods to prevent river overflow.

Urbanisation – The growth of towns and cities, which increases impermeable surfaces and flood risk.

Wetland conservation – Protecting areas where water naturally collects to store excess water and reduce flooding.

River flooding case study: Ganges/Brahmaputra

Bay of Bengal – The sea where the Ganges and Brahmaputra rivers empty, often affected by flooding and tropical cyclones.

Climate change – Long-term shifts in temperatures and weather patterns, contributing to glacier melt and heavier monsoons in this region.

Deforestation (Bangladesh) – Widespread tree loss in the Himalayas and floodplains increases flood risk through higher surface runoff.

Flood Action Plan (FAP) – A project supported by the World Bank to reduce flooding in Bangladesh using embankments, shelters, and warnings, though many parts were unsuccessful.

Ganges River – A major river flowing through India and Bangladesh, central to agriculture and culture, but prone to severe flooding.

Himalayas – The mountain range where both the Ganges and Brahmaputra rivers originate, supplying snow and ice meltwater.

Low-Income Country (LIC) – A country with limited financial resources, like Bangladesh, affecting its ability to invest in flood defences.

Monsoon – A seasonal weather system causing heavy rainfall and flooding during certain months in South Asia.

Padma River – The name for the Ganges in Bangladesh after it joins the Brahmaputra.

Tropical cyclone – A powerful storm system that brings heavy rain and wind, increasing the risk of flooding in Bangladesh.

River pollution

Agricultural pollution – Harmful chemicals like pesticides and fertilisers washing into rivers from farmland.

Chlorine – A chemical used in domestic cleaning and leisure that can harm aquatic life if it enters rivers.

Eutrophication – Excess nutrients in water (often from fertilisers) that lead to rapid plant growth and reduced oxygen, harming aquatic life.

Industrial pollution – Pollution from factories and businesses, such as heavy metals and chemicals, entering rivers.

Organic fertiliser – A natural alternative to synthetic fertilisers that reduces river pollution.

Remediation – The process of cleaning up pollution and restoring the natural environment.

Sewage – Wastewater from homes and toilets that can carry disease if it enters rivers untreated.

Turbidity – Cloudiness in water caused by sediment and pollutants, which reduces oxygen and harms fish.

Wastewater treatment – The process of cleaning used water before it is released into rivers to reduce pollution.

River pollution case study: Nairobi River

Disinfectants – Chemicals used in cleaning that can pollute rivers and harm wildlife.

Heavy metals – Toxic substances (like lead or mercury) from industry and mining that can poison people and animals.

Market gardens – Small farms near the Nairobi River that use polluted water, increasing health risks.

Methane gas – A gas produced by decomposing waste in the river, contributing to foul smells and harmful conditions.

Plastic tax – A proposed charge on plastics to help reduce waste entering the river.

Sanitation system – Infrastructure for safely removing sewage, which is lacking in many areas near the Nairobi River.

Water hyacinth – An invasive plant that spreads quickly due to pollution, blocking sunlight and reducing oxygen in the river.