River Landscapes (P1- SEC C) Flashcards
Upper course characteristics
Steep, V-shaped Valley
Narrow/shallow channel
High bed load
FEATURES :
V draped valleys
Interlocking spurs
Waterfalls
Gorges
Middle course characteristics and features ?
- open , gentle sloping valley with floodplain
- wider /deeper channel
- more suspended sediment
FEATURES :
- meanders
- river cliffs
- slip off slopes
Lower course characteristics and features ?
- open gentle sloping valley with floodplain.
- flat and wide floodplain
- wide open valley
- very wide /deep channel
FEATURES :
Oxbow lakes
Flood plains
Levees
Watershed ?
The boundary dividing one drainage basin from another
Confluence ?
Where 2 river join
Hydraulic action ?
Thé force of water hunting river bed/banks
Abrasion ?
Load carried by river repeatedly hits the bed / banks dislodging particles into the flow of the river
Attrition?
When stones carried by the river know against each other making stones smaller and rounded
Solution ?
River flows over limestone /chalk , the rock slowly dissolved
transportation processes (4)
Traction - large particles rolled over sea bed
Saltation: ‘bouncing of particles too heavy to be suspende
suspension : small sediment held in the river
solution : dissolved load
EROSION LANDFROMS : INTERLOCKING SPURS
- how is it formed and what are they?
outcrops of land along the river course in a valley
- forms near source of river /not powerful enough to cut through ‘spurs of land’ so flows around the
EROSION LANDFROMS : V-SHAPED VALLEY
- how is it formed and what are they?
- as small stream flows downhill steeply, the bedlam erodes downwards
- this vertical erosion deepens the valley, making the sides deeper/exposed
- overtime, weathering/gravity wear away steep valley sides, forcing material into the stream, which it uses to cut valley deeper
EROSION LANDFROMS : WATERFALL S
- how is it formed and what are they?
- SOFTER ROCK erodes quicker undercutting hard rock , creating PLUNGE POOL
- overhang collapses / falls into plunge pool increasing abrasion/ making plunge pool deeper
- waterfall retreats
EROSION LANDFROMS : GORGES
- how is it formed and what are they?
- NARROW, steep-sided valley usually found immediately downstream of a waterfall
- formed by gradual retreat of a waterfall
EROSION LANDFROMS : RAPIDS
what are they?
- FAST FLOWING, turbulent sections of a river where the river bed has a relativley steep gradient
EROSION/DEPOSITION LANDFROMS : MEANDERS/OXBOW LAKES
- how is it formed and what are they?
- as a slight bend in a river occurs, water flows faster on outside bend (erosion) the. inside bend (deposition)
-more exaggerated meanders due to erosion/deposition, so NECK BEGINS TO NARROW - in flood, river cuts the neck taking shortest route - DEPOSITION SEALS OFF OLD MEANDER
- old meander is completely cut off , rive has a new course and ox bow lake is formed
DEPOSITION LANDFORMS : FLOODPLAINS
- how is it formed and what are they?
- wide flat area of Marchy land on either Side of a river
- meanders migrate across floodplain due to LATERAL EROSION -
- when they reach the edge of floodplain , they erode edge of VALLEY - when river floods, loses velocity and it deposits finer sediments
DEPOSITION LANDFORMS : ESTUARIES
- how is it formed and what are they?
- transitional ones between river and coastal environment
- during a rising tide, river water is unable to be discharged into the sea
- river’s velocity falls and sediment is deposited
- deposits form MUDFLATS
- MUDFLATS form into natural habitats called SALTMARSHES
CASE STUDY : river tees
where, what landforms?
- NE OF ENGLAND ( SOURCE HIGH IN PENNINE HILLS)
LANDFORMS : - waterfalls/gorges (erosion)
- meanders (erosion/deposition)
-levees/floodplains (deposition)
factors increasing flood risk
physical/human ?
PHYSICAL
- precipitation - lead to rapid saturation of upper soil, so excess water goes to rivers as surface runoff
- geology - impermeable rocks make water flow overland into river channels
steep slopes - cause greater overland flow/ shorter lag time
HUMAN
- urbanisation - creates impermeable surfaces causing rapid water movement into river channels
- deforestation - when trees are removed, more water available/transferred rapidly to channel - less interception/infiltration
- agriculture- soil is left exposed , leads to more surface run-off
hydrograph?
a graph that plots a river’s discharge after a storm
discharge ?
quantity of water that passes a given point on a stream or river bank within a given period of time
peak discharge ?
highest discharge
lag time?
time in hours between the highest rainfall hughest peak discharge
HARD ENGINEERING: dams and reservoirs
Cost/benefits
Controls the river flow by blocking the river and letting water in a controlled way.
BENEFITS: multipurpose
- effective water regulator
Costs: expensive
- flood large areas
HARD ENGINEERING: embankment
Cost/benefits
Raised river bank - hold more water
BENEFITS: - cheaper
- sustainable
- look natural
COST: concrete walls are unnattraxtive
HARD ENGINEERING: channel straightening
Cost/benefits
Cut through meanders to create straight Channel - speed up water flow
BENEFITS : protects vulnerable location
COST: increase flood risk downstream
- unattractive
- unnatural
- damage habitats
HARD ENGINEERING:
Flood relief channels
AD/DIS
Man made river channel constructed to bypass urban area
Benefit : reduce threat of flood
- reduces losses for those living nearby
DIS : expensive
- regular maintainence
SOFT ENGINEERING : FLOODPLAIN ZONING
Cost /benefit
restricts different land uses to certain locations on the floodplain
BENEFITS: reduce losses from flood
Areas can be used for pasture , parklands and fields
COST : difficult to implement on floodplains , causes land prices to fall
SOFT ENGINEERING : wetlands
Cost /benefit
BENEFITS: - efficient store of water
- valuable habitats to wildlife
COST: takes long for wetlands to establish and grow
SOFT ENGINEERING : RIVER RESTORATION
- course of river changed So river restoration can return it to original course
BENEFIT: reduce likelihood of flood
- more habitats
- restores wetland areas
COST : expensive
- can cause some areas to flood
SOFT ENGINEERING : PREPARING FOR FLOODS /flood warning
COST/BENEFITS
- river basins monitored remotely using satellites /tech by measuring rainfall/river levels
COST : ppl become ‘blighted’ by being at risk of flooding
- property values drop
BENEFITS : helps ppl prepare
- cheaper
CASE STUDY : BANBURY
Location , affected , management
Location : floodplain of river CHERWELL
AFFECTED :
- closure of towns of railway
- 12.5 mill damage
- more 150 Homes/ businesses damaged
MANAGEMENT: - Earth embankment ( holds 3mill m3 of water )
- opening controls rate of flow downstream to Banbury
- raised A361 road
- pumping station to transfer excess water
- Biodiversity Action plan habitat with ponds to store excess water
SOCIAL, ECONOMIC , ENVIRONMENTAL benefits/issues of Banbury ?
SOCIAL: - raised A361 avoided disruption to lives
- quality of life improved
- reduce anxiety of fear of flood
ECONOMIC : - cost £18.5 mill
- donors include ENVIRONMENTAL agency
- benefits are estimated to be over £100 mill
ENVIRONMENTAL : - 100000 tonnes of earth required to build embankment
- new BPA habitat created
-
Flashy storm hydrograph
DESCRIPTION, WEATHER, ROCK TYPE, RELIEF, BASIN SIZE, VEGETATION
- short lag time , high peak , steep rising limb
- intense storm /rapid snow melt
- IMPERMEABLE rocks
- HIGH STEEP SLOPE —> more run off
- small drainage basin
- few plants /deforestation
DEPOSITION LANDFORMS: levees
- how are levees formed and what are they?
- levees are raised embankments alongside a river
- when river floods, friction with land , reduces velocity and increases deposition
- larger material is deposited first at sides of river, and finer material is deosoited further away
- after many floods, sediment builds up to increase height of levées
how do factors that increase flood risk make the hydrograph look like?
Short lag time
Steep rising limb
High discharge
As a result the river may not have the capacity to contain the water and so flood risk is higher
how do factors that decrease flood risk make hydrograph look like?
Longer lag time
Gentle rising limb
Lower discharge
As a result the river is more able to cope with the water entering the channel and the flood risk is lower