what is a drainage basin?
a topographic region from which a stream receives run-off, throughflow and groundwater flow
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what are the topographic barriers that drainage basins are divided by?
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what is stemflow?
the process that directs precipitation down plant branches and stems
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what is percolation?
vertical movement or infiltration of water from the earth's surface to its subsurface
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what is throughflow?
the roughly horizontal flow of water through soil or regolith
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what are some examples of water stores?
oceans, groundwater, glaciers, water held ion vegetation and soil
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what are some examples of slow flows?
groundwater flow through rock, throughflow through soil and ice moving in glaciers
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what are some examples of faster flows?
surface run-off especially in floods, precipitation and evaporation and movement in atmosphere
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what are the two main types of storm hydrographs?
flashy and subdued
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what are some of the factors affecting the shape of the hydrograph?
intensity and duration of rainfall, size and shape of basin, vegetation, temperature, urbanisation and geology
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what does a 'rising limb' on a storm hydrograph indicate?
as surface runoff, throughflow and ground water flow (different speeds) reach the channel, discharge starts to increase
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what does a 'falling limb' on a storm hydrograph indicate?
water is steadily reaching the channel, but in decreasing amounts. Surface runoff may have stopped, but the river is still higher than normal as it is still being fed by increased soil and groundwater
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what are some of the characteristics of a subdued hydrograph?
gentle limbs, low peak discharge, long storm flow, long lag time significant base flow and flooding unlikely, permeable soil and rocks and lots of forestry
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what are some of the characteristics of a flashy hydrograph?
steep limbs, high peak discharge, short storm flow, short lag time, small base flow, flooding unlikely , impermeable soil and rocks and urbanisation of surfaces
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what are some of the permanent features that affect the nature of a basin?
basin shape and size, relief underlying soil and geology and drainage density
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what are some of the temporary features that affect the nature of a basin?
antecedent conditions and vegetation cover
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what are some of the man-made features that affect the nature of a basin?
vegetation change (ie aforestry or deforestation) and urbanisation
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what are the 4 types of erosion?
abrasion, hydraulic action, corrosion and attrition
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what is abrasion?
also known as corrasion, this is when rocks carried along by the river wear down the river bed and banks.
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what is hydraulic action?
a process which is caused by the sheer power of moving water where loose, unconsolidated material is picked up by the frictional drag of flowing water
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what is corrosion?
a process where the river flows over alkaline underlying geology (carbonates- limestone and chalk), minerals in the rock are dissolved by the weak acids in the water. As they are dissolved, they are carried away in the solution
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what is attrition?
the reduction in the size and angularity of particles in the river as they collide with one another, the bed and the banks. Larger,angular load tends to be found near the source whereas small, round load tends to be found near the mouth
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what are the 3 main processes carried out in any river?
erosion, transportation and deposition
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what are some of the factors that determines a river's energy?
gravity acting on the mass of the water, pulling it downwards, altitude of the river (distance to fall- potential energy) and channel gradient (steepness- kinetic energy)
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what are the 4 ways that load can be transported in rivers?
traction, saltation, suspension and solution
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what is traction?
the rolling and sliding of large rocks/boulders along the river bed
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what is saltation?
the 'bouncing' of medium-sized (pebbles/ground) along the river bed
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what is suspension?
the transport of very small load (fine sand/silt/clay) which is continually held up or suspended in the water
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what is solution?
soluble materials (dissolved in water) which are carried via solution transport
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what is river competence?
the maximum size of particle that river is capable of transporting
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what is deposition?
the process by which a river's load is set down/ dropped
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when does a river deposit?
when it no longer has the competence or capacity to carry all of its load (this is why mountain streams are often filled with large boulders)
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what are some of the factors that cause deposition to occur?
when there is a reduction in channel gradient, the river enters a lake or sea, discharge is reduced following a period of low rainfall in areas of shallow water where friction reduces velocity and when there is a sudden increase in load
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what is a Hjulström curve?
a graph that shows the relationship between the size of sediment and the velocity required to erode (lift it), transport it and deposit it
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is more velocity needed to pick up material than to carry it in suspension?
yes (eg it takes more effort to lift something initially than to carry it)
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can only a small decrease in velocity leads to sedimentation/deposition?
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what is a relationship that the Hjulström curve shows?
sand particles are moved by lower pick up velocities than smaller silts and clays and the small clay and silt particles are difficult to pick up as they are sticky and lie on the river bed (cohesion)
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what is another relationship that the Hjulström curve shows?
that once picked up (entrained), particles can be carried at lower velocities than those required to pick them up. For larger particles there is only a small difference between the critical erosion velocity and the settling velocity
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what is the final relationship that the Hjulström curve shows?
the smallest particles are only deposited at very low velocities . Some small clay particles may never be deposited on a river bed, and can be carried almost forever
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what is an example of a well known waterfall?
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what is a waterfall?
a geological formation resulting from a river flowing over an erosion resistant (hard) rock formation that forms a sudden break in elevation
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where do waterfalls form?
in mountain environments where the erosive force is high
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how does a waterfall form?
the soft rock erodes more quickly than the hard rock.The hard rock is left overhanging and it eventually collapses. The fallen rocks crash into the plunge pool causing more erosion. Over time this process is repeated and the waterfall moves upstream
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what is a meander?
a winding curve or bend in a river
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how do riffles and pools form?
when an obstruction in the channel will cause turbulent flow, this causes alternative shallow and deep sections along the bed- these are called riffles and pools
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how does a slip-off slope form?
when the flow on the inside of the bend will become sluggish and inefficient, this leads to deposition and creation of a slip-off slope
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what is a helicoidal flow?
a corkscrew current near the bed that carries eroded material from the outside of the bend to be deposited on the inside of the bend
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what is an ox-bow lake?
a lake formed when the continued narrowing of a meander neck results in the eventual cut through of the neck as two outer bends join
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what is a meander scar/scroll?
feature left behind when the water in an ox-bow lake dries up
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what is a floodplain?
flat areas of land on either side of the river, which form the valley floor of the middle and lower courses
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what determines the width of the floodplain?
the amount of meander migration and lateral erosion occuring
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what are natural levees?
ridge of coarse deposits found alongside the river banks and elevated above the floodplain. Forms from the deposition of alluvium during floods
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how do natural levees increase in size?
when the river overflows the sediment carried is gradually deposited- the heavier material is dumped first- this leads to the banks being built higher
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what is a delta?
a landform that forms from deposition of sediment carried by a river as the flow leaves its mouth and enters slower-moving or standing water
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where is a delta formed?
formed where a flowing river meets a sea or lake ,and slows, depositing material faster than the sea can remove (erode) it
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what are some of the factors that affect a delta's formation?
sediment load, coastal energy, flocculation and seas floor gradient
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what are the two main types of deltas?
arcuate and birds foot
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what is an example of a river where there is an arcuate delta?
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what is an example of a river where there is a birds foot delta?
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what are some of the features of the Nile River's arcuate delta?
has a convex, curved outer edge, it forms an area of well watered land in this desert country and its delta sediments are several km deep,
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what are some of the features of the Mississippi River's birds foot delta?
the delta creates new land which is highly fertile with an abundant water supply and looks like the shape of a birds foot from satellite images
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some of the world's most densely populated areas are on deltas, what are sone examples of these?
North Africa on the Nile, South East Asia on the Mekong and in Western Europe on the Rhine
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what is channelisation?
the process of artificially modifying the natural channel of a river by changing its shape, profile or course
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what are some examples of channelisation?
realignment/diversion (creates a straight shorter route), revetment (protects bank from erosion), re sectioning (increases river velocity effectively) and wing dykes (deflects thalweg)
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what does the channelisation of rivers improve?
flood control, land drainage, navigation and erosion problems
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what is an example of where can man-made levee systems be found?
along the Mississippi and Sacramento rivers
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what is an example of a scheme which is trying to combat the problems that a river causes?
the Lower Mississippi Navigation Scheme
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what are some of the methods used in the LMS scheme?
wing dykes, meander cut-offs, channel dredging and revements
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how much does the ongoing maintenance of this scheme cost?
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what are some of the outcomes of these methods?
the river has started to regain its former length and increased its sinuous plan, concrete mattresses to keep the view in one place which has helped the river hold its shape, and the river has developed and maintained a suitable deep water channel
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what is an example of a LEDC flood
the River Indus flood 2010
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where is Indus loacted?
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what were some of the causes of the flood?
La Niña (unusually intense monsoon rains, worst in the area in 80 years with 200mm in 4 days in some areas), human mismanagement (increased irrigation reduced carrying capacity and flood defenses were neglected) and corruption (lazy gov officials)
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what were some of the short term effects of the flood?
approx 20% of Pakistan's total land area was under water, over 10% of population were affected, 2,000 deaths, 3,000 injured, 1.8 million homes destroyed or damaged, outbreak of diseases and 6 million people needed food aid
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what were some of the long term effects of the flood on the infrastructure and economy?
submerged 69,000km squared of Pakistan's most fertile cropland, killed approx 1.2 million farm animals, agricultural damages were more than $2.9 billion and total agricultural production will fall by 15% and destroyed 2 million bales of cotton
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what approach do the people in Pakistan have to these floods?
a fatalistic approach
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what were some of the responses to the flood?
appeals were immediately launched by international organisations such as the UN, Pakistan's gov also tried to help the huge number of people affected and foreign govs donated millions of dollars such as Saudi Arabia and USA who promised $600 million
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what were some of the problems with some of these responses?
profiteering and corruption where food was in short supply, floods have become a political opportunity for some groups (eg relief made difficult by Taliban insurgents) and US aid was also seen as an opportunity to improve the image of the US
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what is an example of a MEDC flood?
Somerset Levels in 2014
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where are the Somerset Levels located?
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does this area flood naturally?
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what were the 3 causes of this flood?
weather and antecedent conditions (experienced their highest rainfall ever recorded in Jan- nearly 3 times the normal amount) and landscape (low lying coastal plain and wetland), poor flood management (lack of dredging of local rivers eg Tome)
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what were some of the effects of this flood?
6,900ha of agricultural land were under water for over a month- loss of agricultural production, over 600 houses were flooded, local eceonomy suffered and there was the disruption of services including trains on the Bristol and Exeter line)
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what were some of the responses to this flood?
army units were sent to help with flood protection, gov provided and extra £30 million for repairs, after flood the Environment Agency began installing giant pumps and enormoud local support coordinated by FLAG (Flooding on the Levels Action Group)
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what were some of the long term plans proposed to help deal with these floods?
develop an improved management plan, the dredging of Rivers Parrett and Tone near confluence point, proposed improvements to the artificial Sowy River, proposed construction of a tidal barrier and the creation of permanent pumping stations
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which of these proposals were followed thtrough on and now make up the Somerset Flood Action Plan created by the Somerset Rivers Authority?
the 8km dredge of the Tone and Parrett was completed, the environment agency has spent £2.5 million improving pumping infastructure, building new banks, improving pumping capacity and the removal of blockages
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what is channelisation?
a delberate attempt to alter the natural geometry of a river and increase the hudraulic efficiency and allows a larger discharge to be contained within the channel
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what are some of the problems with channelisation?
maintenance cost, increased flood hazards downstream, ecology- habitat destroyed and can be an eyesore, increased erosion
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what are some examples of oft engineering examples?
land use zoning (planning restrictions in area at risk), river restoration (restore meanders and flood meadows), wetland and river bank conservation, tree planting and ensure early warnings are in place
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what are some of the advantages of soft engineering?
cheaper, protects habitat, offers recreational opportunites and is more attractive than channelisation
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what are some of the disadvantages of soft engineering?
restricts farming and is difficult to apply to urban areas
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what is the main purpose of channelisation?
to increase the velocity of the channel flow and its carrying capacity as well`
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Other cards in this set
what are the topographic barriers that drainage basins are divided by?
what is stemflow?
what is percolation?
what is throughflow?
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