Rivers

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What are 'cumecs,' and what do they measure?
Cubic metres per second. They measure discharge and surface runoff.
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How is discharge calculated?
The cross sectional area x the river's main velocity at a particular point in its course.
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What is a hydrograph?
A record of river discharge over a period of time.
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What does a storm hydrograph show?
The change in discharge caused by a period of rainfall.
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What are some factors that affect a hydrograph?
Area, shape, slope, rock type, soil, land use, drainage density, precipitation, temperature, tides, season.
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What is a channel cross profile?
A view of the river bed and banks from one side to another at one point on its course.
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What is the long profile?
A cut out section along the river gradient from source to mouth.
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What is the general profile?
A concave upward curve.
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What are the three main processes of a river?
Erosion, transportation, and deposition.
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What is abrasion?
The scraping/scouring/rubbing of materials carried by the river. It wears down the bed and banks.
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What is hydraulic action?
The power of water moving loose material. Turbulent flow lifts a large number of grains from the river bed, eroding it.
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What is corrosion?
Most effective on rocks that contain carbonates (e.g. limestone, chalk). Minerals in the bed & banks are dissolved by weak acids in the river water.
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What is attrition?
The reduction in size of fragments/particles within a river. They strike one another and the river bed/banks and become smoother, smaller and rounded.
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What is vertical erosion?
When a river tries to cut down to base level, mainly caused by abrasion and hydraulic action - which happens when the river level & velocity are high. Produces steep sided valleys.
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What is lateral erosion?
The river valley widens as the river meanders. Occurs in the middle and lower courses.
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What is traction?
When large stones and boulders are rolled along the river bed by water moving downstream - only occurs at times of high discharge.
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What is saltation?
When small stones bounce along the channel bed, dislodging other particles upwards in relatively high conditions.
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What is suspension?
Very small particles such as sand and silt carried by the river flow.
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What is solution?
Dissolved minerals deposited within a mass of moving water.
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What is deposition?
When a river loses energy, it drops its sediment, with the largest particles first.
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What is the capacity of a river?
The total volume of load it can carry.
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What is the competence of a river?
The diameter of the largest particle it can carry at any given velocity.
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What is a drainage basin?
The area drained by a river and its tributaries.
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What is the watershed?
The ridge/line dividing 2 drainage areas.
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What is a river's regime?
Its annual pattern.
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What is evapotranspiration?
The process of transferring moisture from the earth to the atmosphere by evaporation and transpiration from plants.
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What is groundwater flow?
When water flows through bands of sedimentary rock. The slowest transfer of water.
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What is stem flow?
Water that runs down the stems and branches of plants and trees during/after rain.
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What is throughflow?
Water that moves down a slope through subsoil, pulled by gravity.
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What is infiltration?
The passage of water into soil.
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What is interception?
The process by which raindrops are prevented from reaching the soil surface.
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What is percolation?
The downward movement of water within a rock under the soil's surface.
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What is throughfall?
Water that drips off leaves during a rainstorm.
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What is runoff?
All the water that enters a river and flows out of the drainage basin. It is quantified by measuring the discharge of a river.
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What is precipitation?
Water in any form that falls from the atmosphere to Earth's surface.
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What is rejuvenation?
When the river revives its erosion activity in a vertical direction when the sea level falls or when land surface rises, giving the river more energy.
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How is potential energy calculated?
The altitude of the river's source in relation to its base level.
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What is kinetic energy?
Generated by the flow of the river - converts potential energy to 'moving energy.' The amount is determined by the volume of discharge, the gradient down which it flows and its average velocity.
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What are the characteristics of the upper course's channel?
The channel is narrow and uneven due to boulders on the bed. A rectangular channel. Has a large wetted perimeter.
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What are the characteristics of the middle course's channel?
An asymmetrical channel on the river bends, smooth and asymmetrical on the straight stretches.
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What are the characteristics of the lower course's channel?
The channel widens and deepens further. Sometimes levees occur.
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What is the hydraulic radius?
A measure of efficiency of the channel, calculated using the formula: wetted area of the channel divided by its wetted perimeter. The higher the hydraulic radius, the more efficient the channel.
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What are the three types of delta?
Arcuate, Bird's foot, and Cuspate.
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What is a distributary?
A branch of a river that doesn't return to the main channel after leaving.
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What is the wetted area?
The area of water in the channel, measured in metres squared.
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What is the wetted perimeter?
The total length of bed and banks touched by water, measured in metres.
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What is the bankful level?
The maximum height of water the channel can take without flooding.
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What is the sinuosity ratio?
The actual channel length : the straight channel's length.
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What is the thalweg?
The main flow of the current.
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Why do rivers become more efficient at transportation downstream?
There is less irregular material to cause friction.
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What is an incised meander?
a river meander which has been cut abnormally deeply into the landscape because uplift of the land has led to renewed downward erosion by the river.
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What is a knick point?
A sudden break in the long profile of a river.
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What is a river terrace?
A narrow, flat piece of ground which runs parallel to the river on either side above the floodplain, They are created following a fall in base level due to rejuvenation.
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What is an entrenched meander?
When an incised meander has symmetrical valley sides and a gorge like appearance.
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What is a Hjulstrom Curve?
It illustrates the relationship between the velocity of the flow of a river and its competence.
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What does the Bradshaw Model say increases downstream?
Discharge, occupied channel width, channel depth, average velocity, and load quality.
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What does the Bradshaw Model say decreases downstream?
Load particle size, channel bed roughness, gradient.
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What is discharge?
The average amount of water in the channel.
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What is the occupied channel width?
The average width of channel occupied by water.
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How is the average velocity of a river calculated?
It is the speed of the water flowing a third of the way below the surface in the deepest part of the channel.
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What are some of the causes of flooding?
Excessive precipitation for a short or a long time (excessive precipitation leads to soil saturation), the melting of snow, climactic hazards (e.g. hurricanes), urbanisation (e.g. the impermeability of tarmac, deforestation.)
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What does flood management seek to achieve?
Reducing the frequency and magnitude of flooding, and therefore limiting flood damage.
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What are some methods of hard engineering?
Artificially raising and strengthening banks, parallel lines of flood banks. Removing large boulders from the bed to reduce roughness and increase velocity. Building dams and weirs to regulate the rate at which water passes down a river.
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What are some more methods of hard engineering?
Building diversion channels to divert rivers away from vulnerable areas, dredging to create a deeper channel, so that greater volumes of water can pass through, increasing the height of floodplains by dumping material on it.
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What are even more methods of hard engineering?
Constructing retention basins, into which water is diverted at times of high discharge.
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What are some methods of soft engineering?
Afforestation in the drainage basin, contour ploughing and strip farming in semi arid areas, floodplain zoning - allowing certain areas of the floodplain to flood naturally.
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Other cards in this set

Card 2

Front

How is discharge calculated?

Back

The cross sectional area x the river's main velocity at a particular point in its course.

Card 3

Front

What is a hydrograph?

Back

Preview of the front of card 3

Card 4

Front

What does a storm hydrograph show?

Back

Preview of the front of card 4

Card 5

Front

What are some factors that affect a hydrograph?

Back

Preview of the front of card 5
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