Abrasion: the pebbles being transported wear away the
bed and banks of the river channel.
Alluvium: rock particles (clay, silt, sand and gravel)
deposited by a river.
Attrition: The particles are knocked about as
they are transported, and they gradually become more rounded and reduced in
size.
Base Level: the mouth of the river and the point where
the gradient becomes zero. No further erosion is possible during normal river
flow at this point.
Bedload: the material carried by a river by being
bounced or rolled along its bed.
Catchment: see Drainage Basin.
Confluence: the point at which rivers meet.
Corrosion: see Solution.
Delta: a river mouth choked with sediment causing the
main channel to split into smaller branching channels or distributaries. The
name originates from the Greek for the delta's 'D'-like shape.
Depth: increases downstream, a result of being joined by
a number of tributaries.
Discharge: the amount of water passing a specific point
at a given time. This become larger downstream as a result of the joining of
many tributaries. It is calculated as: cross-sectional area x velocity, and
measured in cubic metres per second (m³/sec).
Distributaries: finger-like river channels which branch
away from a main river channel in a delta.
Drainage Basin: the land that is drained by a river and
its tributaries.
Erosion: the wearing away of the bed and banks of
the river channel by abrasion, hydraulic action, solution and attrition.
Estuary: the tidal mouth of a river, with large, flat
expanses of mud exposed at low tide.
Eutrophication: high nitrate levels combined with
phosphates cause excessive plant and algae growth, a deteriorating process that
results in loss of oxygen and the biological death of the river.
Flood Plain: the wide, flat floor of a river valley. It
consists of sediments (alluvium) deposited by the river.
Freeze-Thaw Weathering: also called
frost-shattering as it occurs in cold climates when temperatures are often
around freezing point and where exposed rocks contain many cracks. Water enters
the cracks during the warmer day and freezes during the colder night. As the
water turns into ice it expands and exerts pressure on the surrounding rock,
causing pieces to break off.
Glaciated Valley a river valley widened and deepened by
the action of glaciers (ice sheets); they become ‘U’-shaped instead of the
normal ‘V’-shape of a river valley.
Gorge: a steep-sided, narrow rocky valley marking the
retreat of a waterfall.
Gradient: the slope of the river profile, steep close to
the source and gradually becoming more gentle until the river reaches sea level.
Hydraulic Action: The sheer force of the water by itself
can erode material from the bed and banks of the river channel.
Interlocking Spurs: As the river descends from the
highland, it begins to meander between spurs which interlock down the valley.
Lateral erosion: erosion by a river on the outside of a
meander channel. It eventually leads to the widening of the valley and the
formation of the flood plain.
Levées: river embankments built by deposition as the
river floods.
Load: the material transported by a river as bedload,
suspended load or dissolved load (in solution).
Lower course: the section of the river near the sea,
where deposition is the most important process and the valley becomes wider and
flatter.
Meander: a bend in a river. The outside of the meander
has the fastest flow and deepest water.
Middle Course: the section of the river between the
mountains and the lowland, where transport of eroded material is important and
the river begins to cut sideways due to the reducing gradient.
Mouth: where a river ends, at a lake or the sea.
Ox-bow Lake: a meander which has been cut off from the
main river channel and abandoned.
Particle Size: range from clay (0.001mm), through silt,
sand, gravel, pebbles, cobbles and boulders (500+mm).
Physical Weathering: the disintegration of rock
into smaller pieces without any chemical change in the rock; this is most likely
in areas of bare rock where there is no vegetation to protect the rock from
extremes of weather e.g. freeze-thaw and exfoliation (or onion weathering).
Plunge Pool: the deep pool below a waterfall.
Point Bar: also known as Slip-Off Slope.
Pot Holes: holes eroded in the solid rock of a river
channel. They are drilled by pebbles caught in eddies in the river.
Profile: the cross-section of the river, from its source
to its mouth, concave in shape.
Rapids: found where the river meets a band of
resistant rock and usually precede a waterfall.
River Cliff: created on the outside of a meander bend by
the erosive effect of fast-flowing water.
Saltation: material bounced along the bed of the
river.
Sedimentation: The settling out of suspended particles
from a body of water (or in some cases, very fine particles settled from the air
or blown by the wind).
Slip-Off Slope: forms on the inside of a meander bend as
a result of deposition in the slower flowing water.
Solution: some rocks such as limestone are subject to
chemical attack and slowly dissolve in the water.
Source: where a river starts, usually in the mountains.
Spur: a narrow neck of highland extending into a river
valley, often forming the divide between two tributaries.
Suspended Load: very small and light material, usually
fine clay and silt, transported by the river in suspension.
Time: an important factor in river erosion and
deposition.
Traction: material rolled along the bed of the
river.
Transportation: the river moves material as bedload,
suspended load or dissolved load (in solution). Bedload can be moved by
saltation or traction.
Tributary: a smaller river that joins a larger one.
Upper Course: the mountain stage of a river with steep
gradients and much erosion.
V-shaped Valley: a deep v-shaped valley is usually found
in the upper course of the river where the water has considerable erosive power.
Velocity: the speed of the water flow.
Waterfalls: form where the river meets a band of softer
rock after flowing over an area of more resistant material. Waterfalls
progressively cut back, leaving a gorge.
Watershed: the highland separating one river basin from
another.
Weathering the break-down or decomposition of rock by
biological, physical or chemical processes.
