Geography terms in Freshwater

An erosion process in which material carried by a river, waves, ice or wind is scraped and bounced against a surface, wearing it away; also called corrasion.

An approach in which management decisions are treated as experiments, monitored, and revised as new information about their effects becomes available.

The planting of trees on land that was not recently forested; replanting land that was recently cleared is reforestation.

A shortage of soil moisture during the growing season that reduces crop yields and pasture, caused by low rainfall, high evaporation or poorly timed rain.

A rapid increase in algae or cyanobacteria in a body of water, usually caused by excess nutrients, which discolours the water and can release toxins.

The amount of water already held in the soil and stores of a drainage basin before a rainfall event, which strongly affects how much of the rain becomes overland flow.

A body of permeable rock or sediment that can store water and allow it to move through it; it is unconfined when open to the surface and confined when sealed by impermeable layers.

A raised embankment of earth, concrete or stone built along a river bank to increase the capacity of the channel and keep floodwater off the land behind it; called a dyke in the Netherlands.

An erosion process in which particles of load collide with each other and break into smaller, more rounded pieces.

The discharge at which a river fills its channel completely, just before it overflows onto the floodplain.

The part of a river's discharge supplied by groundwater seeping slowly into the channel, which keeps the river flowing between storms and in dry seasons.

The lowest level to which a river can erode its bed, usually sea level, or the level of a lake for rivers that drain into one.

An approach in which local communities identify their own water needs and plan, build and maintain solutions, often small-scale and low-cost, with outside support where needed.

A model that summarises how river channel characteristics change downstream, with discharge, width, depth, velocity and load quantity increasing and particle size, bed roughness and gradient decreasing.

The total amount of load that a river can carry at a given discharge.

The upward movement of water through narrow spaces between soil particles, against gravity, which can carry dissolved salts towards the surface.

The modification of a river channel by straightening, deepening, widening or lining it, usually to carry floodwater away more quickly; also called channel modification.

A small, low barrier built across a stream or gully to slow runoff, trap sediment and let water infiltrate and recharge groundwater; the johad of north India is one form.

A computer simulation of the climate system, based on the physics of the atmosphere, oceans, land and ice, used to project future climate under different scenarios of greenhouse gas emissions.

A resource, such as an aquifer or fishery, from which it is difficult to exclude users and where each user's consumption reduces what is left for others.

The involvement of local water users in decisions about the planning, construction, operation, maintenance and financing of water services and resources.

The size of the largest particle that a river can transport at a given velocity.

The funnel-shaped lowering of the water table around a well that pumps groundwater faster than it can flow in from the surrounding aquifer.

A method of appraising a project by comparing its expected costs and benefits, usually in monetary terms over its lifetime, to judge whether it is worthwhile.

The lowest mean velocity at which a particle of a given size is picked up and set in motion by flowing water; also called the entrainment velocity.

A barrier built across a river or stream to hold back water, raise its level or control its flow.

An area of a lake or sea where oxygen levels are so low, usually because of eutrophication, that most aquatic life cannot survive.

The permanent clearance of forest and its replacement by another land use, such as farming, grazing, mining or settlement.

A landform of sediment deposited where a river enters a sea or lake faster than waves and currents can remove it, often divided by distributaries; arcuate, bird's-foot and cuspate are its main shapes.

An approach to water scarcity that reduces or reshapes demand, through pricing, metering, restrictions, efficient technology and education, rather than increasing supply.

The laying down of sediment by a river, waves, ice or wind when its velocity, and so its energy, falls too low to carry the load.

Pollution that enters water from many dispersed sources across a wide area, such as fertiliser runoff from fields, so that no single source can be identified.

The volume of water passing a point in a river per unit of time, found by multiplying the cross-sectional area of the channel by the mean velocity, and measured in m³ s⁻¹ (cumecs).

A channel that branches off from the main river and flows away from it, usually across a delta, to reach the sea separately.

An area of land drained by a river and its tributaries, from which all precipitation that is not lost to the atmosphere flows to the same outlet; also called a catchment.

The total length of all streams in a drainage basin divided by the area of the basin, measured in km per km².

The removal of sediment from the bed of a river, harbour or channel to make it deeper, increasing its capacity or allowing ships to pass.

A method of irrigation that delivers water slowly through pipes and emitters directly to the roots of each plant, reducing losses to evaporation and seepage.

A system that detects or forecasts a hazard and sends timely, understandable warnings to people at risk so that they can act to protect themselves and their property.

A shortage caused by a lack of investment, infrastructure or institutional capacity rather than of water, so that people cannot access water that is physically available.

The benefits people obtain from ecosystems, grouped as provisioning (food, water), regulating (flood control, purification), supporting (habitat, nutrient cycling) and cultural (recreation, heritage) services.

A set of forecasts made by running a weather or flood model many times with slightly different starting conditions, so that the spread of results shows the probability of each outcome.

The quantity, timing and quality of water released or left in a river to sustain its ecosystems and the people who depend on them.

A river that flows only for short periods after rainfall and is dry for most of the year, common in arid regions; an intermittent river flows seasonally.

The wearing away and removal of rock and sediment by a moving agent such as a river, waves, ice or wind.

The tidal mouth of a river where fresh water mixes with sea water, and where tides and waves remove sediment rather than letting it build a delta.

The enrichment of a body of water with nutrients, especially nitrates and phosphates, causing excessive growth of algae and plants and leading to oxygen depletion.

The process by which liquid water is changed into water vapour and returned to the atmosphere from surfaces such as oceans, lakes, soil and wet vegetation.

The combined loss of water to the atmosphere by evaporation and transpiration; potential evapotranspiration (PET) is the amount that would be lost if water were always available.

A measure of water availability as renewable freshwater per person per year, with thresholds of 1,700 m³ for water stress, 1,000 m³ for scarcity and 500 m³ for absolute scarcity.

The part of a storm hydrograph after the peak that shows discharge decreasing as the basin drains; also called the recession limb.

A flood that rises within minutes or a few hours of intense rainfall, usually in a small, steep or urban drainage basin, giving very little warning.

A storm hydrograph with a short lag time, steep rising and falling limbs and a high peak discharge; a subdued hydrograph has a long lag time and a low, broad peak.

An event in which water covers land that is normally dry, for example when a river's discharge exceeds the capacity of its channel and water spills onto the floodplain.

The prediction of when and where a flood will happen and how large it will be, by combining weather forecasts and river measurements with hydrological models.

A graph of annual peak discharge plotted against recurrence interval, usually on a logarithmic axis, used to estimate the size of a flood expected once in a given number of years.

Any action taken to reduce the likelihood of flooding or the harm that floods cause to people, property and the economy.

Actions taken before a flood to reduce its impact, such as flood plans, sandbags, flood boards, raised homes, emergency kits, shelters and evacuation routes.

An artificial channel that takes part of a river's flow around a settlement during high discharge and returns it downstream, reducing the flood level in the main channel.

The likelihood that a flood of a given size will occur in a place combined with the harm it would cause to people, property and activities there.

The wide, flat area of a valley floor on either side of a river that is covered by water during floods and built of layers of alluvium.

Groundwater that accumulated long ago, often in a wetter past climate, and receives little or no recharge today, so it is effectively non-renewable.

Lightly used household wastewater from sinks, baths, showers and washing machines, but not toilets, which can be reused for purposes such as flushing or irrigation.

Water stored in the pore spaces and cracks of rocks and sediments below the water table; its slow movement through rock towards rivers is groundwater flow.

A long-term fall in the volume of groundwater stored in an aquifer, caused when abstraction exceeds recharge.

A corkscrew-like flow of water through a meander bend, in which surface water moves towards the outer bank and returns along the bed towards the inner bank.

A graph that shows the mean velocity at which particles of different sizes are eroded, transported or deposited by a river, plotted on logarithmic axes from laboratory measurements.

The right of every person to sufficient, safe, acceptable, physically accessible and affordable water for personal and domestic use, recognised by the UN General Assembly in 2010.

An erosion process in which the force of moving water, and air compressed into cracks by it, loosens and removes material from the bed and banks of a channel or from a cliff.

A measure of channel efficiency found by dividing the cross-sectional area of a channel by its wetted perimeter; a larger value means less water in contact with the bed and banks and less friction.

Electricity generated by the flow of water through turbines, usually water released from a reservoir behind a dam.

The continuous circulation of water between the oceans, atmosphere, land and living things, driven by solar energy and gravity; at the global scale it is a closed system.

A period in which river flows, lake and reservoir levels and water tables fall well below normal, usually lagging months behind a meteorological drought.

A condition of very low dissolved oxygen in water, usually below about 2 mg per litre, that most aquatic animals cannot survive; anoxia is the complete absence of oxygen.

A surface such as tarmac, concrete or roofing that does not allow water to soak through it, so rainfall becomes overland flow.

The downward movement of water from the ground surface into the soil.

The maximum rate at which water can soak into a soil under given conditions, measured in mm per hour; it falls as the soil becomes wetter or more compacted.

A financial arrangement in which people or businesses pay regular premiums to an insurer, which pays for repairs and losses after an event such as a flood.

The coordinated planning of land and water across a whole drainage basin, regardless of administrative or national borders, involving all stakeholders and balancing economic, social and environmental goals.

A process that coordinates the development and management of water, land and related resources to maximise economic and social welfare equitably without harming the sustainability of ecosystems.

The capture and temporary storage of precipitation by vegetation before it reaches the ground; some intercepted water later evaporates and the rest drips or runs to the ground.

The artificial application of water to land to help crops grow, using canals, flooding, sprinklers, drip systems or pumped groundwater.

A sudden break of slope in the long profile of a river, often marked by a waterfall or rapids, where resistant rock or a fall in base level interrupts the smooth curve.

The time between the peak of rainfall and the peak of discharge in a river, usually measured in hours.

The gradual sinking of the ground surface, often caused by the compaction of clay and silt layers when groundwater is pumped out.

The planning control of what can be built or done on different areas of land, used on floodplains to keep housing and vital services away from the highest-risk zones; also called floodplain zoning.

The downward removal of soluble substances, such as nitrates or salts, from the soil by water percolating through it.

A raised bank along the edge of a river channel; natural levees are built of coarse sediment deposited when floodwater spills out of the channel and loses velocity.

The tendency for flood defences such as artificial levees to encourage more building on the land they protect, so that losses are larger when an extreme flood overtops or breaches them.

A graph or section showing how the height of a river bed changes with distance from its source to its mouth, typically a concave curve that flattens towards base level.

A sinuous bend in a river channel, with erosion on the outer bank and deposition on the inner bank, that migrates across the floodplain over time.

A very large dam, usually more than about 150 m high, with a reservoir of several cubic kilometres or a capacity above 1,000 MW, whose impacts extend across a whole basin.

A period in which precipitation is well below the long-term average for a place, usually over several months; the first stage of a drought.

The risk that people take fewer precautions, or choose riskier places to live, because insurance or a government will pay for their losses.

A dam and reservoir project designed to serve several purposes at once, such as hydroelectric power, irrigation, flood control, water supply and navigation.

An approach to flood mitigation that slows and stores water in a drainage basin using natural processes, for example by planting trees, building leaky dams and restoring wetlands and floodplains.

Water that is produced and put into a supply network but not billed to customers, because of leaks, theft through illegal connections or metering errors.

The forecasting of weather by solving equations of atmospheric physics on supercomputers, starting from observations of the present state of the atmosphere.

The movement of water over the ground surface towards a channel, when rainfall exceeds the infiltration capacity of the soil or falls on soil that is already saturated; also called surface runoff.

A crescent-shaped lake on a floodplain formed when a river cuts through the narrow neck of a meander and deposition seals off the abandoned loop.

The highest discharge reached by a river during a storm or flood event, read from the top of the storm hydrograph.

A wetland in which waterlogged conditions slow decomposition, so partly decayed plant matter accumulates as peat and stores large amounts of carbon.

The slow downward movement of water from the soil into the underlying rock, where it may reach the groundwater store.

A shortage in which natural water supplies cannot meet all demands, including environmental flows; usually defined as more than about 75% of river flows being withdrawn.

Flood mitigation that changes how people use, prepare for and respond to flood-prone land, such as zoning, insurance, warnings and preparation, rather than changing the river itself.

A gently sloping deposit of sand and gravel on the inside of a meander bend, where water is shallow and flow is slow.

Pollution that enters water from a single identifiable place, such as a sewage outfall, factory pipe or slurry tank, so it can be measured and regulated.

The part of a river's discharge during a storm that arrives rapidly by overland flow and fast throughflow, shown as the area above the base flow line on a storm hydrograph; also called stormflow.

The collection and storage of rainwater, from roofs or the land surface, for later use or to recharge groundwater.

An international treaty signed at Ramsar, Iran, in 1971, under which countries commit to the conservation and wise use of wetlands and designate Wetlands of International Importance.

A wetland designated as being of international importance under the Ramsar Convention, which its country commits to conserve.

The downward movement of water from the surface into an aquifer, replenishing groundwater; it may come from rainfall, rivers or irrigation.

The average time between floods of at least a given size, calculated from a long record of annual peak discharges; a 1-in-100-year flood has a 1% chance of happening in any year.

An artificial lake formed behind a dam, in which water is stored for later use.

The settling of sediment in the still water of a reservoir, which reduces its storage capacity and starves the river downstream of sediment.

A country through which a river flows or which borders a river or lake, and which therefore has a stake in how its water is used.

The part of a storm hydrograph that shows discharge increasing from its pre-storm level to the peak, as storm water reaches the channel.

A body created to plan, coordinate or regulate the use of water and land across a whole drainage basin, often across state or national borders.

A steep bank on the outside of a meander bend, formed by lateral erosion where flow is fastest and deepest; also called a cut bank.

The pattern of variation in a river's discharge through an average year, shown on an annual hydrograph of mean monthly discharge.

A hydroelectric project that uses the natural flow of a river with little or no reservoir storage, so that flow downstream stays close to natural.

The accumulation of soluble salts in soil, often caused by irrigation in hot, dry climates, which reduces fertility and can make land unusable for crops.

A transport process in which pebbles and sand grains are lifted by the flow and bounce along the bed in a series of hops.

The movement of seawater into a coastal freshwater aquifer, usually because over-pumping has lowered the water table and the pressure of fresh groundwater.

The mean velocity below which a particle of a given size can no longer be carried by flowing water and is deposited.

A measure of how much a river channel bends, found by dividing the channel length between two points by the straight-line distance between them; values above about 1.5 indicate a meandering channel.

An erosion process in which rock minerals, especially calcium carbonate in limestone and chalk, are dissolved by weakly acidic water; also called corrosion. Dissolved material carried away is the solution load.

A graph showing how the discharge of a river at one point changes over time in response to a period of rainfall, usually drawn with the rainfall as bars on the same time axis.

Physical changes to a river or drainage basin that reduce flooding, such as dams, artificial levees, channel modification and afforestation.

A transport process in which fine particles such as silt and clay are carried within the body of the flowing water, held up by turbulence.

The line joining the deepest and fastest-flowing parts of a river channel along its course; it swings towards the outer bank on bends.

The lateral movement of water downslope through the soil towards a river channel, sometimes concentrated in natural pipes.

An approach in which decisions about water are made by central governments, agencies or large companies and implemented on users, usually through large-scale infrastructure.

A transport process in which the largest particles, such as boulders, are rolled or dragged along the river bed by the force of the flow.

A river, lake or aquifer whose basin or extent crosses the borders of two or more countries, so that its use affects all of them.

The loss of water vapour from plants to the atmosphere, mainly through the stomata in their leaves, after the water has been taken up from the soil by the roots.

The movement of eroded material by a river, waves, ice or wind, by traction, saltation, suspension or solution.

The unequal power between states sharing a river that results from their positions on it, since upstream states can control the quantity, timing and quality of water downstream.

The treatment of used water from homes and industry so that it can be used again for irrigation, industry or, after advanced treatment, drinking.

The process of sharing the available water in a basin between users, sectors and the environment, usually through licences, entitlements or caps.

An equation that accounts for all water entering and leaving a drainage basin over a period: precipitation equals discharge plus evapotranspiration plus or minus the change in storage.

A dispute between countries, regions or groups over the allocation, quality or management of a shared water resource, ranging from diplomatic tension to violence.

Obtaining the same output or service, such as a crop or a product, with less water by reducing losses and waste.

The charges set for water supply and sanitation, which can recover costs, encourage saving and, through lifeline tariffs, protect access for low-income users.

The chemical, physical and biological characteristics of water that determine whether it is safe and suitable for a particular use, such as drinking, irrigation or supporting ecosystems.

The amount of water available in a place over a period of time, measured as a volume or a flow.

A situation in which the available supply of freshwater of acceptable quality is not enough to meet all demands in an area, including the needs of ecosystems.

A condition in which demand for water approaches or exceeds the renewable supply, causing periodic shortages; often defined as less than 1,700 m³ per person per year.

The upper surface of the saturated zone in rock or soil, below which all pore spaces are filled with water; its height rises after recharge and falls in dry periods.

A formal agreement between two or more states that sets out how a shared water resource will be allocated, used or managed, and how disputes will be settled.

A sudden vertical drop in the long profile of a river, often where a band of resistant rock lies over less resistant rock that is eroded more quickly.

The saturation of soil with water, usually because the water table has risen close to the surface, which starves plant roots of air.

The boundary of a drainage basin, usually a line of high ground, that separates water flowing into one river system from water flowing into a neighbouring one; also called a divide.

An area of land saturated or covered by shallow water, permanently or seasonally, such as a marsh, swamp, bog, floodplain or delta, with soils and vegetation adapted to wet conditions.

The return of a degraded or drained wetland towards its natural condition, for example by blocking drains, restoring water flows or replanting vegetation.

The total length of the bed and banks of a river channel in contact with the water at a cross-section, measured in metres.

The Ramsar principle that wetlands should keep their ecological character through sustainable use that benefits people, rather than being strictly preserved without use.

An independent international body (1997–2001) of governments, industry and civil society that reviewed the impacts of large dams and recommended guidelines for fairer dam decisions in 2000.