Freshwater Terms

Abrasion

Is the wearing away of bed and bank by the load carried by the river

Aquifer

Rocks that can hold water

Attrition

Is the wearing away of the load carried by a river. It creates smaller round particles.

Confluence

Where two rivers meet.

Discharge

the volume of water passing a given point over a set time.

Discharge = Area x Velocity

discharge formula

Drainage divide or watershed

the line defining the boundary of a river or stream drainage basin separating it from adjacent basins

Efficiency

Is measured by a rivers hydraulic radius (Cross-section)

Hjulstrom Curve

A graph that shows the relationship between river velocity and particle size when looking at a rivers' ability to erode. transport and deposit.

Hydraulic Action

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

Hydrological Cycle

Closed System

Load

Material transported by a river e.g. stones, sand, boulders.

Maximum sustainable yields

the maximum level of extraction of water that can be maintained indefinitely for a region.

Meander

A bend in the river

Mouth

The end of a river. A river may end in a lake, but more normally in the sea

Potential evapotranspiration

the rate of water loss from an area if there were no shortages of water

Runoff

precipitation that does not soak into the ground but flows over it into surface waters.

Saltation

Heavier particles are bounced or bumped along the bed of the river.

Soil moisture excess

when soil moisture and groundwater is replenished. The excess may lead to saturation and increased surface run

Solution

Is the removal of chemical ions, especially calcium, which causes rocks to dissolve.

Source

The beginning of a river. A river may have multiple sources. The source of a river is normally found in upland mountainous areas.

Suspension

Small particles are held up by turbulent flow in the river.

Tributary

A small river that flows into a larger river.

Velocity

This is the speed that the water in a river is travelling at. The unit of measurement is normally meters a second (m/s). River velocity can be measured using a flowmeter

Water balance

the relationship between the inputs and outputs of a drainage basin

Water Balance Equation

P = Q+ E + delta S

P=precipitation

Q=Runoff

E=Evaporization

S=Change in storage (in soil or bedrock)

Wetted Perimeter

The total length of the bed and the banks in contact with the river.

What are the factors affecting erosion?

Load, Velocity and Discharge, Gradient, Geology, pH, Human Impact

Endorheic/ closed basin

a drainage basin that does not flow out to sea but feeds into an inland body of water or groundwater source, e.g. aral sea tributaries

drainage basins are open systems

• major input: precipitation

• major outputs: evapotranspiration, runoff, leakage

Evapotranspiration

the combined effects of evaporation and transpiration

• account for ~100% of precipitation loss in arid areas and ~75% in humid areas

Potential evapotranspiration :)

water loss that would occur if there was an unlimited supply of water in the soil for use by the vegetation

• moisture availability: the amount of actual water in soil

infiltration capacity

the maximum rate at which rain can be absorbed by a soil in a given condition

Overland flow

occurs mainly when:

• precipitation exceeds infiltration rate

• the soil is saturated

throughflow

water flowing through the soil in natural pipes

percolines

lines of concentrated water flow between soil horizons

base flow

the part of a river’s discharge that is provided by

groundwater seeping into the bed of a river

• relatively constant flow although it increases slightly following a wet period

Interception

water that is retained by plant surfaces and which is later evaporated away or absorbed by the plant

• throughfall: water that either falls through gaps in the vegetation or which drops from leaves, twigs or stems

• stemflow: water that trickles along twigs and branches and finally down the main trunk.

Field capacity

amount of water held in the soil after excess water drains away, that is, saturation or near saturation

Wilting point

the range of moisture content in which permanent wilting of plants occurs

Water table

top layer of phreatic zone

• varies seasonally

phreatic zone

permanently saturated zone within solid rocks and sediments

Recharge

the refilling of water in pores (of rock) where the water has dried up or been extracted by human activity

cryosphere

the snow and ice environment

• Up to 66 per cent of the world’s freshwater is in the form of snow and ice

capacity of a stream

the largest amount of debris that a stream can carry

critical erosion velocity

the lowest velocity at which grains of a given size can be moved

Hjulström curve

shows relationship between velocity of flow and the size of the particle able to be carried, indicates when particle are eroded, carried if already eroded or deposited

Levees

formed by the deposition of coarse material near the channel, while the finer deposits are carried out into the flood plain

flocculation

salt particles group together and become heavier, so they are deposited

• causes formation of river deltas

bioconstruction

vegetation increases the rate of deposition by slowing down the water

Physical water scarcity

where water consumption exceeds 60 per cent of the useable supply

Economic water scarcity

where a country physically has sufficient water to meet its needs, but requires additional storage and transport facilities

water stress

When an area’s per capita water supply is less than 1,700 cubic metres per year

anoxia

oxygen starvation in the water

eutrophication

algal blooms in bodies of freshwater due to runoff from nitrogen-fertilised agricultural land

salinisation

Capillary forces bring water to the surface where it may be evaporated, leaving behind any soluble salts that it is carrying.