Learn: Hydrology, River Processes, and Hazards

Abrasion (corrasion)

Mechanical erosion of soil and rock by abrasive particles moved by water, wind, ice, or gravity.

Abstraction

The act of withdrawing or removing water.

Aeration zone

The area of an unconfined aquifer above the water table where pore spaces are filled with air.

Afforestation

Planting trees on an area of land to create a forest.

Albedo

The measure of how reflective a surface is, represented as a value between 0 and 1.

Albedo effect

The effect produced by the sun's light and heat being reflected back from Earth surfaces into the atmosphere.

Altitude

The height of a place above sea level.

Annual hydrograph

A graph displaying the pattern of water flow or discharge in a river over a year.

Antecedent drainage

A river that maintains its course despite surrounding tectonic uplift or folding.

Antecedent soil moisture

The level of wetness or dryness of the soil before a storm event.

Aquiclude

A geological formation that stores water but does not transmit it easily to wells or springs.

Aquifer

A body of rock and/or sediment that holds groundwater.

Atmosphere

A mixture of gases that surrounds the Earth.

Attrition

An erosional process where rocks and pebbles carried by water collide and wear each other down.

Backswamp

A poorly drained depositional environment in a floodplain where fine silts and clays settle.

Bankfull discharge

The maximum discharge a river channel can carry without flooding.

Baseflow

The portion of streamflow originating from groundwater discharge during dry conditions.

Bed/tracted load

Solid material, such as pebbles, rolled or dragged along the bottom of a stream.

Biosphere

The part of Earth where life exists, encompassing all ecosystems.

Braided river

A river flowing in multiple interconnected channels separated by temporary braid bars.

Canyon

A deep, narrow valley with steep sides cut by a river.

Capacity

The total amount of sediment a river can transport at a specific point.

Carboniferous limestone

A sedimentary rock primarily composed of calcium carbonate, formed 363 to 325 million years ago.

Cavitation

The implosion of bubbles or cavities during rapid, turbulent water flow.

Channel flow

The movement of water within a defined river channel or stream.

Channel storage

The volume of water held within a river or stream channel.

Channelize

The human process of straightening and deepening river channels.

Channels

A landform consisting of a relatively narrow body of water, often a river or strait.

Climate

The long-term pattern of weather in a particular area.

Climate change

Long-term shifts in global and regional climate patterns.

Competence

A river's maximum size of sediment particles it can carry.

Coniferous trees

Trees that bear cones and have needle-like or scale-like leaves.

Corrasion

Mechanical erosion caused by the impact and grinding action of transported materials.

Corrosion (solution)

The dissolving of rocks, particularly limestone and chalk, by acidic water.

Critical erosion velocity

The minimum water velocity needed for a river to pick up and transport sediments.

Dam

A barrier across a waterway to confine and control the flow of water.

Dechannelization

The removal of flood-control channels to reestablish natural water flow.

Deciduous trees

Trees that shed their leaves seasonally to conserve energy and water.

Deforestation

The clearing of forests for uses like agriculture, logging, or urbanization.

Dell

A small, secluded valley or hollow, often with trees or vegetation.

Depressions

An area of low atmospheric pressure characterized by sinking air and precipitation.

Disaster aid

Support provided to individuals affected by disasters to address multidimensional needs.

Discharge

The volume of water flowing through a designated cross-sectional area per unit of time.

Drainage basin

An area of land where all surface water flows downhill into a specific body of water.

Drainage density

The total length of streams in a drainage basin divided by the total area.

Eddies

Circular currents of water.

Entrainment

The process where a fluid flow incorporates and carries along sediment particles.

Evaporation

The process where liquid water transforms into water vapor and enters the atmosphere.

Evapotranspiration (EVT)

The combined processes of evaporation and transpiration from Earth's surface and vegetation.

Event modification

Strategies taken to alter the course, impact, or effects of a natural hazard event.

Field capacity

The amount of water remaining in soil after excess water has drained away against gravity.

Flash flood

A rapid and unexpected flood event occurring shortly after heavy rainfall or dam failure.

Flood

An overflow of water onto normally dry land.

Floodplain

A generally flat area of land alongside a river prone to flooding.

Flood abatement

Strategies and measures taken to reduce the impact of flooding on communities.

Flood diversion

Engineering techniques designed to redirect excess water and prevent flooding.

Geology

The scientific study of the Earth, its rocks, and shaping processes.

Glacial overflow channeling

A trough-shaped channel cut by meltwater escaping from a proglacial lake.

Glacier

A large, persistent body of ice that forms on land and moves under its own weight.

Glen

A narrow and relatively long valley often found in mountainous regions.

Gorge

A narrow valley with steep, rocky walls formed by a river cutting through hard rock.

Gradient

The slope of a line or surface measured as vertical height change over horizontal distance.

Granite

An intrusive igneous rock with a coarse-grained texture rich in quartz, feldspar, and mica.

Groundwater

Fresh water found beneath the Earth's surface in saturated permeable zones.

Gully

A steep-sided channel or valley formed by erosion from running water.

Hard engineering

The construction of artificial structures to protect against erosion and flooding.

Helicoidal flow

A corkscrew-like, spiraling movement of water within a river meander.

Hjülstrom curve

A graph showing the linkage between sediment size and the velocity needed to erode, transport, or deposit.

Hortonian flow

Surface runoff occurring when rainfall intensity exceeds the soil's infiltration capacity.

Human impact

Ways in which human activities alter the Earth's biophysical environment and ecosystems.

Hydraulic action

The force of air and water on the sides of rivers and in cracks.

Hydraulic radius

The cross-sectional area of a channel divided by its wetted perimeter.

Hydrological cycle

The continuous movement and circulation of water on Earth.

Incised meander

A meandering river valley that has cut its bed deep into bedrock due to uplift.

Infiltration

The process of water on the ground surface seeping into the soil.

Infiltration capacity

The maximum rate at which a soil can absorb water.

Infrastructure

Fundamental physical and organizational structures essential for society.

Ingrown meander

An incised meander with an asymmetrical valley shape and steep undercut slope.

Input

Resources or materials that enter a system.

Insurance

An arrangement to provide compensation for specified loss in return for a premium.

Interception loss

Precipitation intercepted by vegetation that evaporates back into the atmosphere.

Intrenched meander

A river bend that has cut deeply into bedrock, creating a steep-sided valley or gorge.

Laminar flow

A smooth, parallel movement of water with no mixing or turbulence.

Land-use zoning

Dividing land into designated areas with specific regulations for development.

Levee

An embankment parallel to a river's banks that serves to contain or divert floodwaters.

Lithosphere

The solid, outermost layer of the Earth, composed of the crust and rigid upper mantle.

Load

The total amount of material transported by a river or stream.

Loss-sharing

An insurance principle where the cost of a loss is distributed among a group.

Manning's equation

An empirical relationship to define depth-averaged velocity of water in open channels.

Meander

A winding, snake-like curve or bend in a river channel.

Moisture availability

A measure of the capacity of a soil to transmit water to a root site.

Open system

A system that allows both energy and matter to be exchanged with its surroundings.

Output

Materials or energy that leave a system.

Overland flow

Water that flows over the land's surface.

Ox-bow lake

A crescent-shaped body of water formed when a river meander is cut off from the main channel.

Peak discharge/flow

The highest level of water discharge in a river or stream after a rainfall event.

Percolation

Water moving downward through soil and porous rock layers to reach groundwater.

Percolines

A hollow at the base of a hillslope where soil moisture seeps out onto the surface.

Permeability

A material's ability to allow fluids to pass through it.

pH

A quantitative measure of the acidity or basicity of solutions.