hydrology

Drainage basin

An area of land drained by a river and its tributaries

Watershed

The boundary separating one drainage basin from another

River discharge

The volume of water flowing through a river channel at a given point and time

Evaporation

The process by which liquid turns into a gas

Transpiration

The process by which water vapour is released into the atmosphere from plants

Evapotranspiration

The combined loss of water from the surface through evaporation and transpiration

Infiltration

The process by which water on the ground surface enters the soil

Percolation

The process by which water moves through the soil and rock pores beneath the surface

Surface runoff

The process by which water flows overland before reaching a river

Throughflow

the horizontal movement of water through the soil towards a river channel

Groundwater flow

The movement of water through saturated rock below the water table

Water table

The upper level of the saturated zone of groundwater

Hydrograph

A graph that shows the discharge of a river over a period of time in response to a rainfall event

Rising limb of a hydrograph

The part of the hydrograph showing the rapid increase in river discharge after a rainfall event

Peak flow on a hydrograph

maximum discharge of a river following a rainfall event

Lag time on a hydrograph

The time difference between the peak rainfall and the peak discharge of a river

Falling limb on a hydrograph

the part of the hydrograph that shows the decrease in river discharge

Base flow on a hydrograph

The steady flow of a river

Flash flood

A sudden, rapid flood which occurs in arid regions with a very short lag time

Floodplain

A flat area of land adjacent to a river, formed by the deposition of sediment during floods

Meander

A bend in a river channel which is found in the middle course of a river

Oxbow lake formation

Meander enlarges, the neck narrows, flood cuts through and deposition seals the end creating an isolated lake

Abrasion

The wearing away of the river bed/ banks due to sediment scraping along the surface

Hydraulic action

Erosion caused by the force of water hitting the channel which compresses the air in cracks

Attrition

The process where particles collide with each other breaking into smaller, rounder pieces

Solution

The dissolving of soluble rocks by the slightly acidic river water

Traction

Large rocks are rolled along the river bed

Saltation

Small pebbles bounced along the river bed

Suspension

Fine particles carried within the water

Solution

The dissolving of soluble rocks by the slightly acidic river water

Riffles

Shallow and fast flow

Pools

Shallow and slow flow

Thalweg

Line of fastest flow in a river channel