Geoscience Reference
In-Depth Information
in the derivation and implementation of the unit
hydrograph.
flux
The rate of flow of some quantity (e.g. the rate
of flow of water as evaporation is referred to as an
evaporative flux).
frequency-magnitude
The relationship between
how often a particular event (e.g. flood) occurs, and
how large the event is. In hydrology it is common
to study low frequency-high magnitude events (e.g.
large floods do not happen very often).
Geographic Information Systems (GIS)
A com-
puter program which is able to store, manipulate
and display spatial digital data over an area (e.g.
maps).
geomorphology
The study of landforms and how
they have evolved.
gravimetric soil moisture content
The ratio of
the weight of water in a soil to the overall weight of
a soil.
groundwater
Water held in the saturated zone
beneath a water table. The area of groundwater is
also referred to as water in the phreatic zone.
groundwater flow
Water which moves down a
hydraulic gradient in the saturated (phreatic) zone.
hillslope hydrology
The study of hydrological
processes operating at the hillslope scale.
Hjulstrom curve
The relationship between water
velocity and sediment erosion and deposition.
Hortonian overland flow
See
infiltration excess
overland flow
.
hydraulic conductivity
A measure of the ability
of a porous medium to transmit water. This is a flux
term with units of metres per second. The hydraulic
conductivity of a soil is highly dependent on water
content.
hydraulic radius
The wetted perimeter of a river
divided by the cross-sectional area.
hydrogen bonding
Bonding between atoms or
molecules caused by the electrical attraction
between a negative and positive ion. This type of
bonding exists between water molecules.
eutrophication
A term used to describe the addi-
tion of nutrients to an aquatic ecosystem that leads
to an increase in net primary productivity. The term
'cultural eutrophication' is sometimes used to
indicate the enhanced addition of nutrients through
human activity. This may lead to problems with
excess weed and algal growth in a river.
evaporation
The movement of water from a liquid
to a gaseous form (i.e. water vapour) and dispersal
into the atmosphere.
evaporation pan
A large vessel of water, with a
measuring instrument or weighing device under-
neath that allows you to record how much water is
lost through evaporation over a time period.
evapotranspiration
A combination of direct evap-
oration from soil/water and transpiration from
plants. The term recognises the fact that much of
the earth's surface is a mixture of vegetation cover
and bare soil.
field capacity
The actual maximum water content
that a soil can hold under normal field conditions.
This is often less than the saturated water content
as the water does not fill all the pore space and
gravity drains large pores very quickly.
flash flood
A flood event that occurs as a result of
extremely intense rainfall causing a rapid rise in
water levels in a stream. This is common in arid and
semi-arid regions.
flood
An inundation of land adjacent to a river
caused by a period of abnormally large discharge or
sea encroachment on the land.
flood frequency analysis
A technique to inves-
tigate the magnitude-frequency relationship for
floods in a particular river. This is based on historical
hydrograph records.
flow duration curve
A graphical description
of the percentage of time a certain discharge is
exceeded for a particular river.
