| Algae
|
Large
and diverse group of simple organisms classified variously between bacteria/fungi
and plants. Blue-green algae (Cyanophyta) are single-celled; green algae
(Chlorophyta) are multicelled and, containing chlorophyll, can photosynthesise.
In lakes, ponds and rivers overrich in nutrients, blanketing growths of
green and blue-green algae (algal blooms) may smother fish and plant life.
See also eutrophication. |
| Anticline |
An
arch-like upfold of rock due to compression in the crust, usually creating
higher ground than the neighbouring syncline. |
| Anticyclone |
A large
region of high atmospheric pressure formed in response to stable subsiding
air. This appears on a weather chart as widely-spaced isobars of between
1000mb to 1040mb. |
| Aquifer |
Permeable
rock, such as chalk or limestone, capable of holding and transmitting
groundwater. A dipping aquifer containing trapped water under hydrostatic
pressure is known as an artesian basin. |
| Baseflow |
The reliable,
expected background level of river discharge maintained by seepage from
groundwater and throughflow. This is the main contributor to a river's
flow during dry weather conditions. |
| BOD |
This
is a measure (in mg/litre or gms/cubic metre) of the amount of oxygen
needed by micro-organisms to break down organic material in the water.
A test sample is stored in darkness for 5 days at 20oC to calculate this.
BOD is thus a measure of how quickly organic matter can de-oxygenate the
water. |
| Bourne |
A seasonal
stream which flows intermittently in a dry valley during periods of wetter
weather when the local water table rises. Many villages in Kent take their
place names from this word e.g. Sittingbourne. |
| Brownfield
site |
A cleared
space in an urban area as a result of urban renewal which offers potential
for new commercial, retail or residential development. The soil may often
be contaminated from previous industrial usage. By contrast, rural space
in previously agricultural land is called a greenfield site. |
| Catchment |
The total
area of land which contributes surface water to a river; also known as
the drainage basin, it is bounded by the watershed. |
| Confluence |
A junction
point between two tributaries of a river. The angle of confluence (acute
upstream) is a useful indication of direction of river flow on a map.
|
| Consent |
A licence
granted by the Environment Agency to discharge effluent of a specified
quality and volume. |
| Containment |
A new
approach to disposal of landfill waste in which the ground is lined with
clay and flexible synthetic membranes preventing leachate escaping and
contaminating the groundwater. |
| Convectional
rainfall |
Thermal
lift of hot, humid air resulting in heavy precipitation from towering
cumulo-nimbus clouds. |
| Cretaceous |
The
geological period in the Mesozoic era stretching approximately from 135
to 65 million years ago. Locally this period includes the Chalk, Gault
Clay, Greensand and Weald Clay formations, postdating the Jurassic period. |
| Depression |
An area
of low pressure (from 970mb to 1000mb) shown on weather charts as a series
of concentric isobars. These are travelling weather systems crossing the
Atlantic in 5-7 days, bringing disturbed unstable weather often organised
along frontal boundaries. See frontal rainfall. |
| Dilution
effect |
The
process by which the concentration of pollution in the water decreases
as discharge increases. |
| Dioxins |
A group
of chemical compounds occurring as unwanted by-products in the manufacture
of certain organo-halogens used in making herbicides, wood preservatives
and many other products. Dioxins remain as contaminants in the finished
products. TCDD, for example, is a contaminant widely used in herbicides,
originating as a defoliant (Agent Orange) in the Vietnamese War. TCDD
is believed to be the cause of serious illnesses e.g. cancer, skin disorders,
genetic disorders in children, etc. |
| Drainage
density |
A measure
of the concentration of rivers in a given area, expressed as km/km2. Values
for Dd vary widely from under 5 in permeable rocks to around 500 in badlands. |
| Dry
valley |
A valley,
usually cut in chalk or karst, with no permanent watercourse along the
valley floor, formed during a periglacial phase of the Ice Age when snowmelt
ran across impermeable permafrost. |
| Effective
rainfall |
Rain
remaining as runoff after all losses by evaporation, interception and
infiltration have been allowed for. |
| Environment
Agency |
Formerly
the NRA (National Rivers Authority), this government agency was set up
by the 1989 Water Act to replace the now defunct regional water authorities.
It was created to be a "guardian of the water environment", with specific
responsibilities nationally for water resources, water pollution control,
flood defence, fisheries, water recreation and navigation. |
| Escarpment |
A distinct
landform with a steep scarp slope and gentle dip slope which forms on
sedimentary rocks which are gently dipping and where differential erosion
has picked out the differences between alternate hard and soft strata. |
| Estuary |
The
stretch of a river mouth directly affected by sea tides. The estuary differs
from a delta in being kept clear by repeated ebb and flood currents; a
delta grows seawards by deposition often because the tide range is smaller. |
| Eutrophication |
The
addition of excessive amounts of nutrients to a water environment, particularly
nitrogen (nitrates) and phosphorus (phosphates). Phytoplankton and algae
thrive in the nutrient-rich conditions, discolouring the water and robbing
it of valuable oxygen as bacteria work overtime feeding on dead remains.
As algae dominate, the growth of water plants is suppressed; these die
first, disrupting the food chain. Death of invertebrates and fish follow
on, and their dead remains in turn lead to additional bacterial activity
during decomposition, reducing oxygen levels still further. See BOD (Biological
Oxygen Demand). |
| Evapotranspiration |
The
loss of moisture to the atmosphere by the combined processes of evaporation
and transpiration. |
| Flash
flood |
A very
sudden, brief and dramatic flood resulting from intense rainfall, snowmelt,
poor interception or poor drainage over urbanised, impermeable surfaces.
See infiltration capacity. |
| Fly
tipping |
The
unregulated and illegal dumping of waste. |
| Food
chain |
A hierarchy
of organisms in a community, each member of which feeds on another in
the chain and is in turn eaten (producers - herbivores - carnivores).
Where organisms eat more than one type of food, this links food chains
together to form a network called a food web. |
| Frontal
rainfall |
Rainfall
formed along distinct bands between two contrasting airmasses in a depression.
A warm front occurs where a sector of warm air rides up and over cold
air. A cold front occurs where cold air drives a wedge underneath lighter
warm air. Cold fronts are the more unstable of the two, and deliver more
intense precipitation. |
| Geology |
The lithology
and structure of rocks at and beneath the earth's surface. It is usual
to distinguish between solid geology (basement rocks) which locally would
be chalk, etc. and drift geology (superficial unconsolidated spreads of
recent material) such as alluvium or river gravels. |
| GQA |
General
Quality Assessment: a scale of river pollution used by the E.A. on a 5-point
system (very good, good, fairly good, fair, poor) based on % dissolved
oxygen and B.O.D. |
| Groundwater |
Water
held underground in rock formations, contained in pores spaces and along
joints, bedding planes and faultlines. Water moves slowly down water table
gradients, eventually returning to the surface as springs or seepage points.
|
| Groyne |
An artificial
construction built out from a shoreline or river bank to collect sediment
and prevent erosion. |
| Heavy
metals |
Metallic
elements of high specific gravity (relative density) including lead, cadmium,
mercury and antimony. |
| Hypothesis |
A prediction
or stated proposition in geography which suggests a relationship between
variables to form the basis for statistical testing. The hypothesis can
be stated in the positive (H 1) or in the negative as a null hypothesis
(H0). |
| Infiltration
capacity |
This
is the maximum sustained rate at which water (rainfall or snowmelt) can
enter the soil. It reflects the permeability of the soil rather than the
porosity. Runoff will occur when rainfall intensity exceeds infiltration
capacity. |
| Lag
time |
The period
of time (usually in hours) between peak precipitation in a drainage basin
and peak discharge on a hydrograph. |
| Leachate |
A concentrated
toxic liquid that seeps from the base of old landfill sites, contaminating
groundwater. Rainfall infiltrates through putrifying organic and inorganic
waste, leaching out heavy metals, ammonia and toxic organic compounds. |
| Meander |
A pronounced
bend in a river with a sinuosity (i.e. ration between stream length and
valley length) greater than 1.5. The wavelength of a meander is about
ten times the channel width. Over time the meander becomes more pronounced
and migrates slowly downvalley. |
| NAPL |
Non-aqueous
phase liquids, the most toxic of complex organic substances used widely
as industrial solvents. These can penetrate groundwater to considerable
depths. Dense NAPLs include chlorinated hydrocarbons and are extremely
useful as solvents, pesticides, herbicides, fire retardants and also as
raw materials from which many plastics are made. Most of these have very
harmful effects at even tiny concentrations (parts per billion). |
| Navigation,
head of |
Inland
extent of river traffic navigation, upstream of the estuary. |
| NNR |
National
Nature Reserves. A national register of high quality conservation areas,
formally designated by English Nature as being of high conservation value,
and subject to strict planning controls. |
| NVZ |
Nitrate
Vulnerable Zones. The EU Nitrate Directive 1991 required countries to
identify areas where nitrate pollution (from agricultural sources) exceeded
the legal limit of 50 mg/litre. |
| Oxygen
debt |
See
Biological Oxygen Demand and Eutrophication. |
| Pericline
|
A small
anticline that pitches along its long axis, giving an elongated dome structure. |
| pH |
A measure
of soil or water acidity on a scale of 1 to 14. Lower pH values refer
to increasing acidity as the hydrogen ion concentration increases. pH
7 is neutral. |
| Phytoplankton |
Microscopic
aquatic plants which float in water. They are extremely productive and
form the basis of all aquatic food chains. |
| Point
source |
Pollution
from a single entry point e.g. a sewage outflow pipe. |
| Pumping
effect |
The
process whereby concentration of chemical pollutants in water increases
with stream discharge. |
| Ramsar
site |
A global
register of the most important wetland habitats in the world, set up by
the Ramsar Convention for Conservation of Wetlands (1976). For inclusion,
a site must contain over 20,000 waterfowl or support 1% of individuals
of one species. |
|
Riparian zone
|
Relating to a river
bank.
|
| Salt
marsh |
Siltation
in estuaries or sheltered bays may create mudflats which become progressively
colonised by salt-tolerant plants. Vegetation helps trap silt particles,
accelerating the silting process until the marsh level is raised above
high tides, rainfall leaches out residual salt, and new potential agricultural
land is created. |
| Scarp
|
(see
escarpment) |
|
Set-aside
|
A payment given
by the EU to farmers to take arable land out of production and leave
it fallow, with the aim of reducing over-production.
|
|
Source
|
Point from which
a stream originates e.g. spring, marsh or lake.
|
|
SPA
|
Special Protection
Area. Internationally important nature conservation sites designated
under the EC Wild Birds Directive, containing rare or vulnerable species.
All SPAs are also SSSIs.
|
|
Spring tide
|
A tide with a considerable
vertical range, forming every 15 days when earth, sun and moon are aligned
at times of full and new moon.
|
|
SSSI
|
Site of Special
Scientific Interest. A site given statutory protection by English Nature
because it has particularly important nature conservation value under
the Wildlife and Countryside Act 1981.
|
|
Storm beach
|
A beach ridge situated
well above the normal limit of high tides, formed as unusually large
waves fling shingle, cobbles and boulders ashore.
|
|
Superimposed
drainage
|
A pattern of rivers
which has been inherited from a higher geological surface, which has
disappeared by long-continued erosion. The effect of superimposition
is to produce discordant drainage in which the pattern of rivers cuts
across the geological grain of an area.
|
|
Syncline
|
Basin-like downfold
of rock, resulting from compression in the earth's crust.
|
|
Terrace
|
A bench-like feature
running along a valley side, roughly parallel with the valley walls,
representing an abandoned floodplain when the river was flowing at a
higher level in the past. The river level may have fallen later in response
to a lowering sea level.
|
|
Tertiary
|
The earliest period
of the Cenozoic geological era dating from 65 million to 2 million years
ago, coming after the Cretaceous period (Chalk) but before the Quaternary
(Ice Age).
|
|
Tidal reach
|
See estuary.
|
|
Tidal surge
|
Or storm surge.
A rapid rise in sea level in excess of normal high tides, due to the
passage of a slow-moving, deep depression in a partly-enclosed sea area.
|
|
Topography
|
The description
of the shape of natural physical features of the earth's surface.
|
|
Tributary
|
Contributory stream
that joins a larger parent river, swelling its discharge. Network analysis
examines the arrangement of tributaries in a hierarchy of 1st, 2nd,
3rd, etc. orders.
|
|
Urbanisation
|
The process of rapid
population growth in cities resulting from a combination of (a) fast
natural increase, (b) in-migration of rural migrants, and (c) area re-definition.
|
|
Water
balance
|
The balance between
inputs (precipitation, snowmelt) and outputs (runoff, evapotranspiration,
soil and groundwater storage changes) in a drainage basin, shown in
a water budget graph.
|
|
Water table
|
The upper surface
of groundwater in saturated permeable rock (see aquifer), which may
rise and fall with the seasons.
|
|
Watershed
|
The water-parting
from which headstreams flow to separate neighbouring drainage basins;
also known as the divide or interfluve.
|
|
Weir
|
Small artificial
dam constructed across a river to maintain water levels to control navigation,
fish stocks, floodwater, etc.
|
|
Wetland
|
Any habitat which
is intermittently or periodically waterlogged including salt marshes,
tidal estuaries, freshwater marshes, bogs, and mangrove swamps.
|
