Rivers Flashcards
What is discharge?
The amount of water in the river.
What is the width of a river?
The number of meters perpendicular to the line of river flow from one side of the river to the other.
What is the depth of the river?
How many meters the river is from the surface to the base.
What is the gradient of the river?
How steep the river is.
What is the velocity of the river?
How fast the river is moving.
What is the sediment size in a river?
How large particles in the river are.
What is the friction of a river?
The surface to volume ratio.
What is the carrying capacity of a river?
How much sediment it can carry.
What is the carrying competence of the river.
The mass of sediment the river can carry.
What are the 4 processes of erosion.
Hydraulic actionAttritionCorrasionAbrasion
What is Hydraulic action?
Waves breaking at the foot of a cliff force air in cracks to be compressed. Loose rocks are dislodged and removed. When the wave retreats the compressed air rushes out of the crack and can further weaken faults in the cliff face.
What is attrition?
Attrition is when rocks carried by seawater collide – gradually making them smaller and smoother.
What is Corrasion?
Corrasion is when rock caught up in surging waves are hurled at a cliff face – causing it to be chipped and gauged.
What is Abrasion?
Abrasion is the sandpaper effect of loose rocks being scraped along bare rock. It often smooth’s and polishes the rock.
What is transportation?
Transportation is movement of sediment by the action of waves.
What are the 4 processes of transportation?
Traction, Saltation, Solution, Deposition
What is traction?
Traction involves the rolling of large and heavy rocks along the seabed.
What is a Saltation?
Saltation involves smaller material being bounced along the seabed.
What is Solution?
Sediment that has dissolved completely will be transported in solution.
What is suspension?
Suspension is when lighter sediment is suspended within the water. This often discolours the water close to the shore.
What is deposition?
Deposition occurs when energy levels decrease in environments such as bays and estuaries. Where deposition occurs on the inside of a spit a salt marsh can form.
Describe a river delta.
This is a ‘D’ shaped area of sandy/ muddy sediment built up into the open water where the river meets the sea.
Where is the line of fastest flow in a river?
The thalweg.
What is a Levee?
If a river floods, material is deposited on the banks, the material that is dropped first is the coarsest, and creates a natural embankment
What happens to levee when the water in the river is low.
When the amount of water in the river is low deposition takes place, the bed of the river rises and flooding is again likely. In some countries, artificial levees are put in place to reduce the flood risk.
What defines the amount of energy available for fluvial processes such as erosion and transport.
The vertical distance to the sea at any given point in a rivers course - Potential energy.The discharge, volume of flow per second.
Where is the rivers energy used?
The rivers energy is primarily used in overcoming friction.95% is used for friction, any surplus available will cause erosion and sedimentation.
When do streams and rivers achieve peak energy?
At bank full discharge which is when the river is the most efficient, moving the most water and sediment for the lest amount of energy expended.
What is base flow?
Rate of discharge in a stream where only the throughflow and groundwater flow from subsurface aquifers contribute to the overall flow.
What does a river need to be in equilibrium?
Friction and energy must be in balance.
What could cause an increase in discharge?
A change in the weather.
How would a river respond to an increase in discharge.
By eroding more.
What returns a river back to equilibrium?
Negative feedback.
How would you describe a v-shaped valley?
This is a valley whose typical cross section is shaped like a ‘v’.(a cross section is the shape that you would walk if you walked down one side of a valley and up the opposite side).(the long profile is the shape that you would walk if you walked from the river’s source to its mouth).
Explain a V-shaped valley.
explanation - As the river cuts down into the landscape in an upland area, gravity and mass movements roll material down the valley sides to give the valley a typical ‘v’ shape.
Describe a floodplain.
- This is an area of flat land found on either side of a river. This usually becomes wider as the river nears its mouth.
Explain a flood plain.
The flood plain is the area of land which is flooded when a river overflows its banks. In this area layers of alluvium are laid down. The soils are thus thick and fertile and the land is flat.
Describe a levee.
- These are mounds of alluvium piled up along the river’s edge.
Explain a levee.
explanation - These are formed by the river depositing the coarsest part of its load (pebbles, gravel and sand) close to the river channel when the river floods. This happens because usually when the water overflows the river bank its speed (and therefore its ability to transport alluvium) is greatly reduced.Sometimes these are built by people in an attempt to prevent the river flooding.
Describe a meander.
description - These are bends (loops) in the river. explanation - Lateral (sideways) erosion of the river channel results in the river forming a winding pattern. (tip! if a river or stream has an absolutely straight pattern then it is probably artificial i.e. a canal).
Explain a meander.
- As the water flows down a river, its speed is faster on the outside of the meander causing erosion and slower on the inside of the meander resulting in deposition.
Describe an ox-bow lake.
- This is a truncated (cut off) section of a meander in the river channel which forms a ‘c’ shape.
Explain an ox-bow lake.
- This is formed by the loops in a meander eroding the flood plain until eventually the loop in the meander is left cut off from the main river channel.
Describe a river delta.
- This is a ‘D’ - shaped area of sandy / muddy sediment built up into the open water where a river meets the sea.
Explain a river delta.
- Where a river meets the sea or a lake and its speed is slowed down, then deposition on its bed can lead to braiding taking place. This deposition results in the river bed being built up out into the sea.
Describe a gorge.
- A narrow steep sided valley
Explain a gorge.
This feature is formed where a river is cutting through a band of hard rock. Where a waterfall has cut back.
Describe a pothole.
- A round hole in the riverbed
Explain a pothole.
- Formed by abrasion as a pebble is rolled around by turbulence in a circle on the bed
Describe interlocking spurs.
- Slopes that the river flows around, like dragons’ teeth, down the valley
Explain interlocking spurs.
- The river cannot force its way through, so must flow around at the bottom of the hill.
Describe a point bar / slip of slope.
- A slope made of gravel and sand on the inside of a meander
Explain a point bar / slip of slope.
- The river flows slowly on the inside of the bend so material is deposited.
Describe a river cliff.
- A steep, possibly overhanging, bank on the outside of a meander
Explain a river cliff.
- The river flows faster on the outside of the meander so it erodes.
Describe a waterfall.
- A steep drop in the bed of a river causing the water in the river to fall vertically.
Explain a waterfall.
- Waterfalls occur where a band of harder rock crosses the path of a river. The river is less able to erode this harder rock and leaves it as a step in the river’s long profile.
What are the characteristics of the source of a river?
Steep/V-Shaped valleyNarrow/shallow channelHigh bed-load.
What are the characteristics of the middle course of a river?
Open/gentle sloping valley with floodplain.Wider/deeper channel.more suspended sediment.
What are the characteristics of the mouth of a river?
open gentle sloping valley with floodplain.Flat and wide flood plain.Wide, open valley.Very wide and very deep channel.
What are the features of the middle course of a river?
MeandersRiver cliffsSlip off slopes
What are the features of the source of a river?
‘V’ shaped valleysInterlocking spurs water falls
What are the feature of the mouth of a river?
Ox-box lake Flood plainsLevees
What does the amount of energy available for a river depend on?
The vertical distance to the sea at any given point in a river’s course –Potential EnergyThe Discharge (volume of flow per second).
What is a river’s energy primarily used in overcoming?
Friction.95% of energy is used in overcoming this.If surplus energy is available, erosion and sediment transport will occur.
What three zones can a drainage basin be split up into?
Sediment Supply Zone –Upper CourseSediment Transfer Zone –Middle CourseSediment Storage Zone –Lower CourseEach zone exhibits distinctive channel and valley landforms
Explain the characteristics and profiles of the upper valley section of river.
Vertical erosion with hydraulic action, abrasion & attrition dominant processes.Traction and saltation at high flow.Load size is large and angular.V-shaped valleys.
Explain the characteristics and profiles of the middle reaches section of a river.
Channel is deeper and wider.Vertical erosion decreasing in importance, more lateral erosion and deposition.Suspension is the main transportation type.Load becomes smaller and less angular.
Explain the characteristics and profiles of the lower reaches of a section.
Channel is at its widest and deepest, and may be tidal.Deposition more important than erosion.Fine material deposited.Large amount of load but the size is very small and very rounded.
Water flow is subject to which two main forces?
Gravity and and Frictional Resistance.
Describe laminar flow.
Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection. When a fluid is flowing through a closed channel such as a pipe or between two flat plates, either of two types of flow may occur depending on the velocity and viscosity of the fluid: laminar flow or turbulent flow.
Describe turbulent flow
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and flow velocity in space and time.
What is a drainage basin?
A drainage basin is an area of land drained by a river and its tributaries (river system). It includes water found in the water table and surface run-off. There is an imaginary line separating drainage basins called a watershed. Usually, this is a ridge of high land.
What is a hydraulic radius?
The hydraulic radius is defined as the ratio of the channel’s cross-sectional area of the flow to its wetted perimeter (the portion of the cross-section’s perimeter that is “wet”):The efficiency of a streams shape is measured by the hydraulic radius.
How do you calculate the hydraulic radius?
HR = Cross-sectional Area /Wetted Perimeter
What is Mannings N?
Manning’s n is a co-efficient of roughness•It is a number that tells us how rough the channel is –so we know how much friction is slowing down the water.
How do you calculate mannings N?
V=R 2/3 S 1/2 / Nv= velocityR= hydraulic radiusS= slopen= roughnessA high-value indicates a rough bed.
What is the critical erosion threshold?
Point reached where the forces tending to move particles are just balanced by the resisting force of friction.
What is Fluvial Erosion?
The removal of rock and other mineral particles from the channel bed and banks by stream flow.
What is Entrainment?
Sediments in stream channels also experience a lifting force that contributes to erosion:Flow velocity = higher on top of sediment= lower on base of sedimentPressure difference which dislodges particles.
What is the material being carried by a river called?
Its load.
What is deposition in channel called?
Deposition in the channel = Aggradation
What is the Hjulström Curve?
It is a graph to show that if a particle is very small 0.001 or 0.1 mm there is less lift as there is less pressure difference between the top of the particle and the bottom.
What is a braided channel?
A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars or, in British usage, aits or eyots. Braided streams occur in rivers with high slope and/or large sediment load.
What is a floodplain?
An area of low-lying ground adjacent to a river, formed mainly of river sediments and subject to flooding.
What is a Alluvial fan?
An alluvial fan is a fan- or cone-shaped deposit of sediment crossed and built up by streams. If a fan is built up by debris flows it is properly called a debris cone or colluvial fan.
What are Pools and riffles?
In a flowing stream, a riffle-pool sequence (also known as a pool-riffle sequence) develops as a stream’s hydrological flow structure alternates from areas of relatively shallow to deeper water. This sequence is present only in streams carrying gravel or coarser sediments.
What are river terraces?
river terrace (stream terrace) Fragment of a former valley floor that now stands well above the level of the present floodplain. It is caused by stream incision, which may be due to uplift of the land, to a fall in sea level, or to a change in climate.
What does the themes region comprise of?
The Thames region comprises of the drainage basin of the Thames and its tributaries.
How does the development of the themes compare to the rest of the UK?
It is the most developed area of the UK with a population of 12 million.
Describe recreation and leisure in the themes basin.
It is used for fishing, swimming, canoeing, rowing, sailing, cruising, guided tours and walking. The Cotswold Park is an extremely important to the area due to the wide range of water activities in the lakes. Oxford contains many sports grounds whilst entertaining punting and rowing on the rivers.
Describe energy development in the themes.
Obviously, the gradient of the themes is not steep enough to produce hydro-electric power however many of its tributaries such as the river Windon have been used by mills. Barges also use the river to carry waste to incinerators.
Describe two flood defence systems for London.
The Thames barrier is a flood defence providing a high standard of protection to the 420,000 houses. The floodplains of the Thames, and its numerous tributaries, provide important flood alleviation which decrease discharge in the floodplain prior to reaching major urban areas downstream.
Describe a flood defence systems for Oxford.
One of the main flood alleviation facilities for Oxford Port Meadow due to the restored meanders and floodplain of the river Cole.
In the themes basin; how do farms adapt to flood plains?
In areas that flood livestock farming may be more suited as animals can be led to dry land in floods and crops are not ruined.
In the themes basin; compare farming on the upper and lower parts of the river valley.
The lower parts of river valleys are good for farming due to the availability of flat land and water for irrigation, whereas the upper parts of the basin the conditions are cooler, wetter and steeper, meaning it is less suited to arable farming.
In the themes basin; How much water is abstracted per day from the region?
Every day approximately 4700 million litres of water is abstracted from the Regions Rivers and groundwater.
In the themes basin; How many times can water falling in the Cotswold be used?
Rain falling on the Cotswold can be used up to 8 times before it reaches the themes estuary.
Briefly describe industry on the themes.
The area contains natural resources such as sand however the primary use of the river remains to be to allow exports and imports.
Why are river basins important to people?
To be used for, land for industry, land for farming, land for residential, leisure, transport, water supply (everywhere is in a river basin)
Where is most of the water, and where is most of the fresh water?
97% of water on earth is in the sea, fresh water is mainly stored as ice in polar regions.
On average, how much water do people use per day?
The average person uses 150 L per day.
What are the main things people use water for?
Toilet flushingBath showerDishwasherdrinkingwashing machineoutsidemiscellaneous
