Term
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Definition
| Combination of evaporation and transpirations |
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Term
| Overland Flow (Surface Run-off) |
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Definition
| Water that flows directly over the land's surface without infiltrating. |
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Definition
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Term
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Definition
| The process by which water turns into a gas |
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Definition
| Precipitation collected and stored by vegetation |
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Term
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Definition
| Movement of water between air, land and sea |
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Term
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Definition
| All forms of rainfall which deposit rainfall on the Earth's surface |
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Term
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Definition
| Water loss from vegetation by evaporation |
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Term
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Definition
| Water that seeps into the ground |
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Term
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Definition
| Water that seeps deep into underlying bedrock |
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Term
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Definition
| Conversion of gas to liquid |
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Term
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Definition
Balance between water inputs and outputs of a drainage basin.
Precipitation=Runoff+Evaporation+/-Change in storage |
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Term
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Definition
| Rainfall caused by heating of the earth's surface by the sun causing formation of large cumulonimbus clouds above the condensation point. These clouds produce heavy rain. |
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Term
| Relief/Orographic Rainfall |
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Definition
| Rainfall caused as air carried by revailing winds is forced to rise above an area of high land causing condensation, and thus rainfall. |
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Term
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Definition
| An area of little or no rain created on the landward side of raised terrain due to evaporation of moisture. |
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Definition
| Rainfall caused by movements of air masses. Warm Air is less dense than Cool Air and thus it rises and condenses causing moderate to heavy rainfall. |
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Term
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Definition
| The volume of water flow including suspended and dissolved material which passes through a given cross sectional area. |
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Term
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Definition
| These display the variability of discharge of a river over the course of a year. |
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Term
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Definition
| A diagram which illustrates the changes in discharge of a river and precipitation over the period of a storm/flood |
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Term
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Definition
| The time taken between peak discharge and peak rainfall |
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Term
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Definition
| Water which reaches the channel mainly through slow throughlow. |
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Term
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Definition
| Water which reaches the channel rapidly through overland flow and rapid throughflow. |
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Term
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Definition
| Forces of Water against bed and banks |
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Term
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Definition
| Bed and Banks worn down by river's load |
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Term
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Definition
| Load carried by river collide and smooth particles down and break them into smaller pieces. |
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Term
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Definition
| Chemical action of river water. Acids slowly dissolve the bed and banks |
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Term
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Definition
| When large sediment such as boulders roll along the river bed. |
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Term
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Definition
| Sand sized particles bounced along the river bed by the flow of water. |
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Term
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Definition
| Fine clay and sand particles carried along a river. |
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Term
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Definition
| Dissolved materials (e.g. Calcium Carbonate) |
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Term
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Definition
| An illustration of the relationship between particle size and velocity. |
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Term
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Definition
| The volume of sediment a river can transport. |
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Term
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Definition
| Maximum size of load a river is capable of transporting. |
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Term
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Definition
| The reference to a side on view of the whole course of a river in order to show changes in gradient. |
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Term
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Definition
| The equilibrum long profile a river always attempts to reach, but in reality is impossible to reach. |
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Term
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Definition
| Stored energy fixed by altitude of river/stream in relation to its base. |
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Term
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Definition
| Energy determined by volume of flowing water, changes in gradient and changes in velocity. |
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Term
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Definition
| Uninterrupted, parallel flows within a river which occurs in less sinuous and deeper sections of a river. |
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Term
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Definition
A model to show changes in river channel characteristics with distance downstream.
< Discharge
< River Width
< Depth
< Velocity
< Load quantity
> Load Particle Size
> Channel Bed Roughness
> Gradient
(Missed- < Wetted Perimeter
< Hydraulic Radius) |
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Term
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Definition
Also known as kettles or chuckholes, these appear as rounded holes and are found in the upper course. They tend to start initially as a depression or crack which is increased in size by abrasion. The swirling current left behind is known as an eddie.
GletscherGarten, Switzerland
Blyde River Canyon, South Africa |
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Term
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Definition
Rapids are found in the upper course and appear as cascades with 'white water' where both turbulence and velocity are high. When water flows over rock of varying resistance, some obstacles are formed increasing turbulence. However, the gradient is also increased.
E.g. Del Moines Rapids, Mississippi, Illinois
Asakawa River Rapids, Tokyo |
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Term
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Definition
Appears as a near vertical drop of water along the river flow. When flowing water meets a band of less resistant rock after more resistant rock, the softer rock is eroded by hydraulic action forming a step. The continued repetition forms a waterfall. At the bottom of the waterfall, a plunge pool is formed. Abrasion and hydraulic action cause undercutting of waterfall. Over time, the waterfall retreats upstream whilst increasing in size. A gorge is left behind.
E.g. Niagara Falls, USA/Canada
Angel Falls, Venezuela |
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Term
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Definition
Where the river takes a winding course in the middle and lower course. Meanders originate in times of flood when sediment is deposited in some areas to form riffles. The river takes the path of least resistance winding around the riffles forming pools. The repeated process creates a meander. Sinuosity > 1.5
E.g. Blackfoot River, Montana River, USA
Mississippi River, New Orleans, USA |
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Term
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Definition
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Term
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Definition
| The corkscrew shaped flow found within meanders. The river is deepest on the outside of the bend and shallowest on the inside. |
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Term
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Definition
| A gentle decline on the inside of a meander bend formed by deposition. Velocity is slow and the river is shallow. |
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Term
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Definition
| Formed on the outside of a river bend where flow is fastest mainly by erosion from abrasion and hydraulic action. Velocity is high and the river is deep. |
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Term
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Definition
| Continued erosion on the outside and deposition on the inside will narrow the meander neck until it is broken through at a time of flood. |
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Term
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Definition
| Meanders migrate laterally becoming more sinuous due to deposition on the inside and erosion on the outside. Deposition on the upstream side and erosion on the downstream side will cause the meander to shift downstream. |
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Term
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Definition
| A term used to describe how meandering a river is. (Actual Channel Length/Straight Line Distance from Source to Mouth). < 1 is straight, > 1 is sinuous. |
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Term
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Definition
| Where a river splits into one or more channel forming a pattern which resembles the strands of a braid. They appear much like land deltas. A reduction in competence or capacity causes load deposition and aggradation creating small islands along the river channel. To avoid these braid bars, the river takes the path of least resistance subdividing the river. An increase in discharge will cause the river to return to one single channel. E.g. Rakaia River, NZ |
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Term
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Definition
Floodplains are the wide areas of flat land found either side of the river. They are prominent in the middle and lower course and can help limit flood damage. Lateral Migration of meanders widens the floodplain until further migration is prevented by bluffs (areas of high relief). The floodplain surface is high in nutrients due to aggradation.
E.g. Mississippi River Floodplain, New Orleans |
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Term
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Definition
A mound of sediment found parallel to the bank which appear as raised river banks. When a river floods, there is increased friction along the floodplain reducing velocity and competence of the river. As the river moves further away from the main channel, competence decreases further. This means that larger sediment is deposited nearer to the bank and finer sediment is deposited further away. Repeated flooding will form a larger levee.
E.g. River Danube, Germany
Yangtze River, China |
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Term
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Definition
| Landform formed when a river meets a body of still water causing deposition. Deltas appear somewhat like an uprooted tree with many branches. A fall in velocity and flocculation (clumping of lay particles when contacted with saltwater) cause deposition settling on the bed. An arcuate delta (e.g. Nile Delta) are characterised by gently curved sides and are formed by longshore currents. Birdfoot Deltas have long protrusions and are formed when marine processes are weak and river discharge is high (Mississippi Delta, Louisiana/Gulf of Mexico). Cuspate Deltas (E.g. Ebro Delta, Spain) are traingular in shape and are formed by very gentle marine processes acting against river flow. |
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Term
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Definition
| The renewal of a river's powers of downward/vertical erosion |
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Term
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Definition
| Changes in level of land relative to the sea. (Mainly isostatic rebound; the removal of glaciers reduces pressure and causes land to 'bounce back') |
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Term
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Definition
| Changes in the sea-level caused by an increase in the volume of water. Occurs on a global level. (E.g. Melting of Icecaps) |
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Term
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Definition
| Increase in land height as a result of crust compression at convergent plate boundaries. |
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Term
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Definition
| Landforms created by a relative fall in sea level. MARINE REGRESSION |
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Term
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Definition
| Landforms created by a relative rise in sea level. MARINE TRANSGRESSION |
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Term
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Definition
| The points at which there is a sudden break of slope in the long profile of a river. They show themselves as rapids or waterfalls (e.g. Thornton Force, River Twist, Yorkshire). Knickpoints mark the position of the former base sea level and are formed by emergence. The river will work its way towards equilibrium. |
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Term
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Definition
| Terraces are flat areas of land found either side of the river channel which mark former floodplains. Over time,sequences of terraces may build up. Vertical erosion caused by rejuvenation lowers the floodplain. E.g. River Severn, Ironbridge, Shropshire |
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Term
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Definition
| Paired terraces are level on each side of the floodplain since vertical erosion is dominant. |
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Term
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Definition
| Terraces are at varying heights on the side of the floodplain and are asymmetrical since lateral erosion is dominant. |
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Term
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Definition
| Gorge-Like Meanders formed when a meandering river resumes downward erosion forming a valley. |
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Term
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Definition
Incised Meanders formed when vertical erosion is dominant giving little time for the river to change course. A symmetrical gorge-like valley is formed.
E.g. San Juan River, Utah |
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Term
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Definition
Meanders created by a combination of lateral and vertical erosion. Incision is gradual allowing the meander to shift sideways producing an asymmetric cross section. A slip off slope and river cliff will remain.
E.g. River Wye, Tintern, Wales |
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Term
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Definition
| The construction of a physical structure designed to restrict river flooding. Hard Engineering tends not to work in harmony with the environment and schemes are usually expensive. |
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Term
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Definition
| Schemes to reduce flooding which work in harmony with the environment. |
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Term
| Channelisation (River Straightening) |
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Definition
HARD
Cutting meanders to increase gradient and increase velocity taking water away from an area. Channelisation may also improve navigation.
However, the river's erosive power is increased and there is potential for rejuvenation. Flood risk downstream can also be increased and ecosystems will be affected.
E.g. Mississippi River, River Rhine |
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Term
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Definition
| Piping placed to retain water underground. However, culverts can leak or be blocked by sediment. |
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Term
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Definition
HARD
A raised river bank to increase capacity of a river. However, the collapse of a levee can have devastating effects and water may become trapped inland. This method also prevents deposition of nutrient rich sediment and can cause aggradation.
E.g. Yellow River, China
Mississippi River, USA |
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Term
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Definition
HARD
A physical wall constructed to hold back the river and increase depth. Like channel straightening, walls can increase flood risk downstream since channel efficiency is raised. They are used in urban areas since they use up minimal land.
E.g. Thames, London, UK
Swan River, Perth, Australia |
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Term
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Definition
HARD
A dam controls flow of water and a reservoir is built up upstream. They can create leisure facilities (e.g. Kielder Water, Northumberland) and allow the production of HEP (e.g. Three Gorges Dam,Hubei Province, China) but poses great risk if it fails (e.g. Vaiont Dam, Vaiont River, Venice Region collapsed in 1963 killing 2000+). They can also cause water supply disputes (e.g. Aswan Dam, Nile). |
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Term
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Definition
HARD
A barrier across a river designed to alter flow characteristics of a river normally through the creation of steps. Very Rarely Used. |
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Term
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Definition
HARD
Secondary river channel alongside main channel to increase water capacity.
E.g. Morganza Spillway, Mississippi River
Jubilee River, Thames, UK |
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Term
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Definition
HARD
Area of water allowed to flood from which water is pumped back into the river after the flood recedes.
Ohrtbrookgarden, Germany |
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Term
| Flood Warning & Preparation |
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Definition
SOFT
Warning people in advance allowing preparation for a flood. For Example, in the UK, the Environmental Agency gives out warnings based on rainfall and discharge readings. E.g. Cockermouth Floods, River Derwent, 2009 |
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Term
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Definition
SOFT
Allowing certain areas to flood and protect more valuable structures. House prices suddenly collapse in unprotected areas. |
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Term
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Definition
| Returning the river towards its equilibrium. |
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Term
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Definition
SOFT
Improving river quality towards original ecosystem level by fixing aspects of streams. |
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Term
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Definition
SOFT
A process designed to improve river quality although the finished product will not resemble the original ecosystem. |
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