Geoscience Reference
In-Depth Information
areal rainfall
The average rainfall for an area (often
a catchment in hydrology) calculated from several
different point measurements.
artesian water or well
Water that flows directly
to the surface from a confined aquifer (i.e. it does not
require extraction from the ground via a pump). The
water in aquifer is under pressure so it is able to
reach the surface of a well.
AVHRR (Advanced Very High Resolution
Radiometer)
A North American Space Agency
(NASA) satellite used mainly for atmospheric
interpretation.
bankfull discharge
The amount of water flowing
down a river when it is full to the top of its banks.
baseflow
The portion of streamflow that is not
attributed to storm precipitation (i.e. it flows
regardless of the daily variation in rainfall).
Sometimes also referred to as slowflow.
Bergeron process
The process of raindrop growth
through a strong water vapour gradient between ice
crystals and small water droplets.
biochemical oxygen demand (BOD)
A measure
of the oxygen required by bacteria and other micro-
organisms to break down organic matter in a water
sample. A strong indicator of the level of organic
pollution in a river.
Bowen ratio
The ratio of sensible heat to latent
heat. This is sometimes used within a method to
measure evaporation from a surface.
Boyle's law
A law of physics relating pressure (
P
),
temperature (
T
), volume (
V
) and concentration of
molecules (
n
) in gases.
canopy storage capacity
The volume of water
that can be held in the canopy before water starts
dripping as indirect throughfall.
capillary forces
The forces holding back soil water
so that it does not drain completely through a soil
under gravity. The primary cause of capillary forces
is surface tension between the water and soil
surfaces.
catchment
The area of land from which water
flows towards a river and then from that river to the
sea. Also known as a river basin.
channel flow
Water flowing within a channel. A
general term for streamflow or riverflow.
channelisation
The confinement of a river into
a permanent, rigid, channel structure. This often
occurs as part of urbanisation and flood protection.
cloud seeding
The artificial generation of pre-
cipitation (normally rainfall) through provision of
extra condensation nuclei within a cloud.
condensation
The movement of water from a
gaseous state into a liquid state; the opposite of
evaporation.
condensation nuclei
Minute particles present in
the atmosphere upon which the water or ice droplets
form.
convective precipitation
Precipitation caused by
heating from the earth's surface (leading to uplift of
a moist air body).
covalent bonding
A form of molecular bonding
where electrons are shared between two atoms in the
molecule. This is the strongest form of chemical
bond and exists within a water molecule.
cyclonic precipitation
Precipitation caused by a
low-pressure weather system where the air is con-
stantly being forced upwards.
dewfall (or dew)
Water that condenses from the
atmosphere (upon cooling) onto a surface (frequently
vegetation).
dilution gauging
A technique to measure
streamflow based on the dilution of a tracer by the
water in the stream.
discharge
In hydrology discharge is frequently
used to denote the amount of water flowing down
a river/stream with time (units m
3
/s, called
cumecs).
effective rainfall
The rainfall that produces storm-
flow (i.e. is not absorbed by soil). This is a term used
