Running Water and Groundwater

Hydrologic cycle

The continuous movement of water between Earth’s atmosphere, oceans, and land through processes like evaporation, condensation, precipitation, and runoff.

Evaporation

The process by which water changes from a liquid to a gas or vapor, primarily due to heat from the sun.

Infiltration

The movement of water from the surface into the ground through soil and rock layers.

Runoff

Water that flows over the land surface toward rivers, lakes, or oceans rather than soaking into the ground.

Transpiration

The release of water vapor from plants into the atmosphere through small pores in leaves.

Evapotranspiration

The combined process of water loss from evaporation and transpiration from land and plants.

Drainage basin (watershed)

The land area that collects and channels precipitation to a single stream or river system.

Divide

A ridge or elevated region that separates one drainage basin from another.

Headward erosion

The process by which a stream lengthens its channel upstream by eroding back toward its source.

Dendritic pattern

A drainage pattern resembling tree branches, common in regions of uniform rock resistance.

Radial pattern

A drainage pattern where streams flow outward from a central high point, such as a volcano or dome.

Rectangular pattern

A drainage pattern where streams follow intersecting sets of fractures or joints, forming right angles.

Trellis pattern

A drainage pattern where tributaries run parallel to ridges and join main streams at right angles, typical of folded terrain.

Laminar flow

Smooth, parallel flow of water in which particles move in straight paths without mixing.

Turbulent flow

Chaotic, swirling water movement where particles mix and move in many directions.

Gradient

The slope or steepness of a stream channel, usually expressed as the vertical drop over a given distance.

Discharge

The volume of water flowing past a specific point in a stream per unit of time, often measured in cubic meters per second.

Longitudinal profile

A cross-sectional view of a stream from its source to its mouth showing changes in elevation.

Pothole

A circular depression in a streambed formed by the grinding action of sediment and rock fragments in swirling water.

Dissolved load

The portion of a stream’s load carried in solution, consisting of ions from chemical weathering.

Suspended load

Fine particles like silt and clay carried within the water column without settling.

Bed load

Larger particles such as sand, gravel, and pebbles that roll, slide, or bounce along the streambed.

Settling velocity

The speed at which particles fall through still water due to gravity.

Saltation

A process where sand-sized particles move by bouncing or skipping along the streambed.

Capacity

The total amount of sediment a stream can carry.

Competence

The maximum particle size a stream can transport.

Sorting

The process by which sediments are separated by size and density due to transport and deposition.

Alluvium

Sediment deposited by a stream, typically found in riverbeds, floodplains, and deltas.

Meander

A bend or curve in a river channel formed by lateral erosion and deposition.

Cut bank

The outer, erosional side of a meander bend where the water’s velocity is highest.

Point bar

The inner, depositional side of a meander bend where sediment accumulates.

Cutoff

A new, shorter stream channel formed when a meander is cut off from the main flow.

Oxbow lake

A crescent-shaped lake formed when a meander cutoff becomes isolated from the river.

Braided channel

A stream channel consisting of multiple interweaving channels separated by bars of sediment.

Stream valley

The entire area shaped by stream erosion and deposition, including the channel and surrounding slopes.

Base level

The lowest point to which a stream can erode, often sea level or a lake.

Floodplain

The flat area adjacent to a river that is periodically inundated during floods.

Incised meander

A meander that is deeply cut into the landscape due to renewed stream downcutting.

Stream terrace

A flat, elevated surface along a valley representing an old floodplain left behind after downcutting.

Bar

A ridge of sediment, such as sand or gravel, deposited in a stream channel or along its banks.

Delta

A landform created where a stream enters a standing body of water and deposits sediment in a triangular or fan shape.

Distributary

A smaller stream that branches off and flows away from the main river channel within a delta.

Natural levee

A ridge of sediment deposited along a riverbank during floods.

Back swamp

A poorly drained area behind natural levees that often remains wet or marshy.

Yazoo tributary

A small stream that runs parallel to a larger river for some distance before joining it, blocked by natural levees.

Alluvial fan

A fan-shaped deposit of sediment formed where a stream flows from a mountain onto a flatter plain.

Flood

An overflow of water onto normally dry land due to excessive rainfall, snowmelt, or failure of dams or levees.

Groundwater

Water that fills the pores and fractures in underground soil and rock layers.

Zone of saturation

The subsurface zone where all pores are completely filled with water.

Water table

The upper surface of the zone of saturation.

Unsaturated zone

The subsurface area above the water table where pores contain both air and water.

Porosity

The percentage of a material’s volume that consists of open spaces or pores.

Permeability

The ability of a material to transmit water through connected pores.

Aquitard

A layer of rock or sediment that restricts groundwater movement due to low permeability.

Aquifer

A body of permeable rock or sediment that stores and transmits groundwater.

Well

A hole drilled into the ground to access water from an aquifer.

Drawdown

The lowering of the water table around a well due to groundwater withdrawal.

Cone of depression

A cone-shaped lowering of the water table around a pumped well.

Artesian system

A confined aquifer system where groundwater is under pressure and flows upward without pumping.

Confined aquifer

An aquifer trapped between impermeable layers, keeping the water under pressure.

Spring

A natural flow of groundwater to the surface where the water table intersects the ground.

Perched water table

A localized zone of saturation above the main water table, caused by an impermeable layer.

Hot spring

A spring that discharges groundwater heated by geothermal energy.

Geyser

A fountain of hot water and steam that erupts periodically due to pressure buildup underground.

Cavern

A naturally formed underground chamber or series of chambers, often created by the dissolution of limestone.

Stalactite

An icicle-like deposit hanging from the ceiling of a cavern, formed by dripping mineral-rich water.

Stalagmite

A cone-shaped deposit that rises from a cavern floor, formed by dripping mineral water from above.

Karst topography

A landscape formed by the dissolution of soluble rocks like limestone, featuring sinkholes, caves, and disappearing streams.

Sinkhole (sink)

A depression or hole in the ground caused by the collapse of a cavern roof or the dissolution of limestone.