Geoscience Reference
In-Depth Information
GLOSSARY
acid rain
Acidic rain that forms in the atmosphere
when industrial gas emissions (especially sulphur
dioxide and nitrogen oxides) combine with pre-
cipitating water (NB rain is naturally acidic - acid
rain has an enhanced acidity from industrial
emissions).
actual evaporation
Evaporation which occurs
at a rate controlled by the available water (e.g.
plant transpiration may be restricted by low soil
moisture).
advective energy
energy that originates from
elsewhere (another region that may be hundreds or
thousands of kilometres away) and has been trans-
ported to a region (frequently in the form of latent
heat) where it becomes available energy.
aerodynamic resistance
A term to account for the
way that the water evaporating off a surface mixes
with a potentially drier atmosphere above it through
turbulent mixing. It is a measure of aerodynamic
roughness. NB This is directly inverse to aero-
dynamic conductance.
albedo
The reflectivity of a surface (a unit per-
centage).
alkalinity
A measure of the capacity to absorb
hydrogen ions without a change in pH (Viessman
and Hammer, 1998). This is influenced by the
concentration of hydroxide, bicarbonate or carbon-
ate ions.
amenity value
A term used to denote how useful
an area (e.g. a stretch of river) is for recreation and
other purposes.
anemometer
Instrument for measuring wind
speed.
annual maximum series
River flow data used in
flood frequency analysis. It takes the highest flow in
every year of the period.
aquifer
A layer of unconsolidated or consolidated
rock that is able to transmit and store enough water
for extraction. A confined aquifer has restricted flow
above and below it while an unconfined aquifer has
no upper limit.
aquifer storage and recovery (ASR)
A water
resource management technique involving the addi-
tion of surface water into an aquifer for storage to
be recovered later.
aquifuge
A totally impermeable rock formation.
aquitard
A geological formation that transmits
water at a much slower rate than the aquifer (similar
to aquifuge).
