Freshwater

Drainage basin

The area drained by a river and its tributaries

Watershed

The boundary separating one drainage basin from another

Hydrological cycle

The continuous movement of water between atmosphere, land and oceans

Open system

A system with inputs, outputs, stores and transfers

Input

Water entering the system (e.g. precipitation)

Output

Water leaving the system (e.g. evaporation)

Store

Where water is held (e.g. soil, aquifers, vegetation)

Transfer

Movement of water (e.g. runoff, infiltration)

Precipitation

Water falling from atmosphere (rain, snow, hail)

Evaporation

Loss of water from surfaces into atmosphere

Transpiration

Loss of water from plants

Evapotranspiration

Combined evaporation and transpiration

Interception

Precipitation caught by vegetation

Infiltration

Water soaking into soil

Percolation

Water moving from soil to rock layers

Throughflow

Lateral movement of water through soil

Groundwater flow

Movement of water in aquifers

Overland flow

Water flowing over land surface

Baseflow

Groundwater feeding rivers

Aquifer

Permeable rock that stores water

Water table

Upper level of groundwater

Saturation point

When soil cannot hold more water

Field capacity

Maximum water soil can retain after drainage

River discharge

Volume of water flowing in a river per second

Hydraulic radius

Efficiency of river channel (cross-section / wetted perimeter)

Velocity

Speed of river flow

Load

Sediment carried by a river

Competence

Largest particle a river can carry

Capacity

Total load a river can carry

Erosion

Wearing away of river bed and banks

Hydraulic action

Erosion by water force compressing air

Abrasion

Erosion by sediment scraping

Attrition

Sediment colliding and breaking down

Solution

Chemical erosion

Transportation

Movement of sediment

Traction

Rolling large particles

Saltation

Bouncing particles

Suspension

Fine particles carried in water

Solution

Dissolved materials carried in water

Deposition

Dropping of sediment when energy decreases

Hjulstrom curve

Relationship between velocity and erosion/deposition

Waterfall

Vertical drop in river due to erosion

Meander

Bend in river channel

Oxbow lake

Cut-off meander

Floodplain

Flat area formed by deposition

Levees

Natural raised river banks

Delta

Deposition at river mouth

Hydrograph

Graph showing river discharge over time

Peak discharge

Maximum flow during a storm

Lag time

Time between rainfall and peak discharge

Rising limb

Increase in discharge

Falling limb

Decrease in discharge

Urban hydrograph

Hydrograph with short lag time and high peak discharge

Rural hydrograph

with long lag time and lower peak

Flooding

Overflow of water onto land

Flood risk

Likelihood of flooding occurring

Flood magnitude

Size of flood event

Flood frequency

How often floods occur

Hard engineering

Large-scale artificial flood control (e.g. dams)

Soft engineering

Natural flood management methods

Dams

Barriers storing water and controlling flow

Channelization

Straightening rivers

Levees (artificial)

Embankments to contain river

Flood relief channels

Artificial channels to divert water

Afforestation

Planting trees to reduce runoff

Floodplain zoning

Restricting building in flood areas

River restoration

Returning river to natural state

Water scarcity

Lack of sufficient water supply

Physical water scarcity

Insufficient water due to natural factors

Economic water scarcity

Lack of access due to poverty/infrastructure

Drought

Prolonged period of low rainfall

Water stress

Demand exceeds supply

Water quality

Condition of water for use

Pollution

Contamination of water

Eutrophication

Excess nutrients causing algal blooms

Salinization

Salt build-up in soil from irrigation

Groundwater depletion

Overuse of aquifers

Sustainable water use

Using water without depleting resources

International water conflict

Disputes over shared water resources

Water management

Strategies to control water supply

Integrated drainage basin management (IDBM)

Coordinated management of water resources

Multipurpose dams

Dams used for energy, water supply and flood control

Wetlands

Areas saturated with water supporting ecosystems

Ramsar Convention

International agreement to protect wetlands