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The Geography Sited
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River / Fluvial Revision Notes

These terms are the bare minimum vocabulary you should be able to use and understand when sitting the examination. You are free to download this page for your own educational use.

Aquifer
A bed of rock which allows water to percolate through it and accumulate within the spaces between the rock particles.
Artesian Well
A type of well from which water flows without assistance. This is caused by the base of the well being in rock layers which are saturated and contain water under pressure. The pressure, called hydrostatic pressure is generated by the top of the well being below the level of the water supply. This can occur when a well is sunk in the base of a valley, and the porous rocks it exploits extend some distance up the sides of the valley.
Bedload
The load of a stream or river which is moved along its bed.
Bourne
A type of stream, common in the chalk areas of Southern England, which flows only during the wetter parts of the year when the water table rises above the bed of the stream. For the remained of the year the watertable is below the stream bed, leaving the stream dry.
Catchment Area
The catchment area, or drainage basin, of a river is the land area which drains into the river. All rainfall in the catchment area of a river will flow into the river. A valley will usually form the catchment area for the river which flows in its base. Rain falling in the next valley will flow into a different river.
Clints
A weathered block of limestone surrounded by Grykes, the weathered joints of the rock. Clints and grykes are typical of limestone pavements and karst landscapes.
Consequent River
A river which flows down the slope of the landscape in the direction of the rock dip. Literally the river is a 'consequence' of the slope.
Coombs
A hollow in the side of a chalk valley, or sometimes another word for a corrie.
Cut Off
A meander in a river course which is literally cut off from the present river. When a meander has almost formed a complete loop, the narrow neck of land may be eroded in flood conditions, allowing the river to by-pass the bend. Silt begins to build up at the entrances to the cut off section, eventually creating a lake known as either a cut off or an ox-bow lake.
Delta
A triangular area of deposited silt or alluvium at the mouth of a river. It will occur where a river carries a heavy load and empties into a shallow sea. As the area of silt increases the river tends to divide into many smaller channels. The mouth of the Nile in Egypt forms a fan shaped delta known as an arcuate delta. The more lobate delta at the mouth of the Mississippi is known as a bird's foot delta.
Dendritic Drainage
A drainage pattern which resembles the trunk and branches of a tree when viewed from above. Small streams (twigs) flow into larger streams (small branches) which in turn flow into small rivers (large branches). The small rivers eventually all flow into a single main river (the trunk).
Dry Valley
A valley, usually on either limestone or chalk, which should contain a stream but doesn't. This is caused by the water table level being below the land surface. All rain permeated through the porous rock to join subterranean water courses.
Earth Pillars
A very tall column of soil protected by a large rock perched on top. The rock protects the soil beneath it from erosion caused by rainfall. Earth pillars may be twenty or more feet high and occur most frequently in mountainous areas.
Flood Plain
A flat area of land on either side of a river. The soil consists of alluvium which is deposited every time the river floods and overflows it's banks. The land tends to be slightly higher along the edges of the river where a levee forms
Gorge
A valley with vertical walls created by the headward migration of a waterfall. As the waterfall retreats due to erosion, a gorge is formed downstream. Good examples occur downstream of the Niagara Falls in Canada, and below High Force on the River Tees, UK.
Gradient
The angle of slope down which a river or stream flows. A steep gradient is typical of a young mountain stream, whilst a gentle gradient is typical of a mature lowland river.
Grykes
The weathered joints in limestone which surround clints. The grykes are weathered and enlarged by chemical weathering of the limestone, eventually leaving an isolated block of limestone, a clint, surrounded on all sides by grykes.
Gully
A small ,narrow and usually long channel on a hillside created by flowing water.
Infiltration
The process by which rain water soaks into and through the ground.
Karst Landscape
The classical landscape of Limestone areas, featuring limestone pavements, caves, swallow holes, and other limestone features. Almost all drainage is below the surface, leaving the ground very dry and barren. The name Karst comes from the area of Yugoslavia along the Adriatic coast.
Knickpoint
An abrupt change in slope or gradient of a river, often characterised by waterfalls or rapids over hard rock areas. It is caused by uplift of the land or a drop in sea level leading to rejuvenation.
Landslide
The mass movement of earth and rocks down a slope. Landslides are often caused by soil becoming too heavy to remain stable due to saturation by rainwater, or by earth tremors such as volcanic eruptions and earthquakes.
Lateral Erosion
A river valley is widened by erosion of the valley sides. This is lateral erosion. The deepening of the valley due to river action is vertical erosion. In youthful rivers, vertical erosion is the most active form, whilst in mature rivers, lateral erosion is more pronounced than vertical.
Levees
Raised banks of alluvium along the edges of an old river. When a river floods its banks, the water spreads out and rapidly loses its load carrying ability. Deposition occurs close to the banks, increases their height. When not flooding, sediment is deposited on the river bed. After a period of time the river and its levees stand above the general level of the surrounding flood plain.
Meander
A bend or curve in the course of a river. The river constantly alters the shape of a meander by eroding the outside of the bend and depositing sediment on the slipoff slope, the inside of the bend.
Mouth
The part of a river where it enters the sea, a lake or even another larger river.
Oasis
An area within an arid desert area where water is present at or near the surface. Clusters of Date Palms are typical indicators of an oasis within the Sahara Desert.
Ox-Bow Lake
A meander in a river course which is literally cut off from the present river. When a meander has almost formed a complete loop, the narrow neck of land may be eroded in flood conditions, allowing the river to by-pass the bend. Silt begins to build up at the entrances to the cut off section, eventually creating a lake known as either a cut off or an ox-bow lake.
Peneplain
A large area of almost flat land. The area is eroded flat by the action of rain and river erosion. More resistant rocks may as isolated sections above the general level of the land. A highland peneplain is known as a plateau.
Percolation
The movement of water down through the soil or cracks in rocks.
Pervious
Something which allows water to pass through it due to cracks or defects is pervious. A pervious rock differs from a porous one in that a porous rock allows water to flow throuFebruary 24, 2006ement through the pores. For example, solid granite is neither porous nor permeable. Granite containing cracks and faults may allow water to pass. It then becomes permeable, but is still not porous.
Plunge Pool
A deep pool which forms at the base of a waterfall. Water and its load gain velocity by falling at a waterfall thus increasing erosion directly below the fall. Once a depression forms, currents cause pebbles to swirl around within it, increasing the erosion and thus the depth of the plunge pool.
Porous
A porous substance allows water to pass through it, making use of the spaces between the pores. Rocks such as sandstone are porous since they allow water to penetrate the gaps between the rock particles.
Pot Hole
A vertical hole into which a surface stream flows, or used to flow. Pot holes occur in limestone areas where subterranean drainage is developed. The Pot Hole is the route taken by the water from the surface to the underground drainage. It may also be known as a sink hole or a swallow hole.
Radial Drainage
When rain falls on the top of a dome shape it may run off the surface in any direction. Domed areas such as Dartmoor in the South West of the UK exhibit radial drainage. When viewed from above the pattern of rivers resembles the spokes of a wheel, the hub being the top of the dome.
Rapids
When a river crosses a band of hard rock differential erosion occurs. The hard rocks erode less quickly than the softer rocks below them. This steepens the river gradient and increases the velocity of the water. A waterfall or rapids will be formed where the water rushes over the hard rocks producing white water as it speeds down the steepened section.
Rejuvenation
When land is uplifted, or the base level of a river is lowered for any reason, the river's erosive power is increased. The gradient down which it flows is increased and it's powers of vertical erosion are also increased. The river becomes more active and is literally rejuvenated.
Riffle
An area of a river which is wide and shallow, the water flowing over a pebble bed with protruding rocks. Friction is high due to the shallow depth and rough bed. Riffles occur between pools, which are located within meanders. Water flow is divergent at a riffle, and convergent in pools.
River Basin
The area of land drained by a main river and its tributaries. See catchment area
River Cliff
The outer bank of a meander experiences considerable erosion and is often concave and relatively high when compared with the inner bank. It forms a cliff like structure, hence the name river cliff.
Run Off
Rainfall which flows across the surface rather than sinking into the ground.
Sink Hole
A vertical hole into which a surface stream flows, or used to flow. Pot holes occur in limestone areas where subterranean drainage is developed. The Pot Hole is the route taken by the water from the surface to the underground drainage. It may also be known as a pot hole or a swallow hole.
Slip Off Slope
The inside edge of a meander. The inside edge of a meander is characterised by slow flow, deposition and the creation of a gently sloping profile which creates progressively deeper water as distance from the inner bend increases.
Solution
The part of a river's load which is dissolved in the water. An example is Calcium Carbonate which is dissolved from limestone by acidic water. See Stalactite and Stalagmite for more information about Calcium Carbonate in solution.
Source
The point at which a river starts.
Spring
A natural source of water rising out of the ground. A spring will occur where the watertable is at the surface. Where rain water percolates through permeable rocks then meets an impermeable layer the water will flow along the boundary. If that boundary happens to occur on a hillside, the water will appear as a series of springs along the side of the hill. This line is the spring line.
Stalactite
A formation of Calcium Carbonate which hangs down from the roof of a cave or similar structure within limestone rocks. Water rich in dissolved Calcium Carbonate ( see solution ) seeps through the roof and, as it drips, some of the Calcium Carbonate is left deposited on the roof. Over a considerable period of time the Calcium Carbonate accumulates to form an icicle shaped formation which grown downwards. See Stalagmite
Stalagmite
Similar to a stalactite in formation, a Stalagmite is formed when drips of Calcium Carbonate rich water fall onto the floor of a cave. As the drip hits the floor some of the dissolved Calcium Carbonate is deposited. Over a period of time the deposit accumulated forming a column of Calcium Carbonate growing up from the floor. Due to the splashing of the drips, Stalagmites are generally wider and more robust than stalactites.
Subsequent River
A river which does not flow down the main slope of the land. See Consequent River and Trellis Drainage .
Suspension
The part of a river's load which is carried as particles held in the water. It is load in suspension which gives water a cloudy appearance. See bedload and solution
Swallow Hole
A vertical hole into which a surface stream flows, or used to flow. Pot holes occur in limestone areas where subterranean drainage is developed. The Pot Hole is the route taken by the water from the surface to the underground drainage. It may also be known as a pot hole or a sink hole.
Trellis Drainage
This form of drainage develops on a surface composed of alternate layers of hard and soft rocks which all dip in the same direction. A main river will develop which flows in the direction of the slope. This is a Consequent River . It is fed by rivers which form in the vales on either side. These rivers will follow the softer bands of rock which are generally at right angles to the main river. The overall pattern resembles a trellis, hence the name.
Tributary
A river or stream which feeds a larger water course.
Vertical Erosion
Vertical erosion is caused by the erosive action of rivers cutting downwards. This deepens river valleys. The valley is widened by lateral erosion
Water Table
The level of the groundwater, or the level below which the rocks are saturated with water. During dry weather the water table will sink, and during wet weather it will rise nearer to the surface. The lowest point to which the watertable sinks is known as the permanent watertable. See Zone of intermittent saturation,Zone of non-saturation and Zone of permanent saturation .
Waterfall
When a river crosses a band of hard rock differential erosion occurs. The hard rocks erode less quickly than the softer rocks below them. This steepens the river gradient and increases the velocity of the water. A waterfall or rapids will be formed where the water rushes over the hard rocks producing white water as it speeds down the steepened section. The waterfall may occur at the sight of a Knickpoint
Zone of intermittent saturation
The area between the normal level of the watertable and the level it reaches after heavy rainfall. This area is only saturated during periods of wet weather.
Zone of non-saturation
The area of the ground between the surface and the top of the watertable. Water always passes through this zone which never becomes saturated.
Zone of permanent saturation
The part of the ground in which the pores are always saturated with ground water.

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