river landscapes
- Created by: Devika_C
- Created on: 05-01-20 21:41
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- river landscapes
- key words
- DRAINAGE BASIN : area of land drained by a river and its tributaries
- SOURCE: the start of the river
- TRIBUTARY: a small stream that joins a larger river
- WATERSHED: the edge of a river basin
- MOUTH: the end of a river (where is joins at the sea)
- LONG PROFILE: shows how the gradient of a river changes downstream
- UPPER COURSE: steep
- erosion landforms
- INTERLOCKING SPURS: mountain stream erodes vertically creating a v-shaped valley. it winds around areas of resistant rock which juts out into the valley
- WATERFALLS: river flows downstream and erodes less resistant rocks which creates STEPS - the steps then become a waterfall
- GORGES: is a narrow, steep-sided valley found downstream of a retreating waterfall
- erosion landforms
- MIDDLE COURSE: gentle
- erosion and deposition landforms
- MEANDERS: bends in the river found in lowland areas
- THALWEG: is the line of fastest current
- erosion on the outside bend and deposition on the inside bend
- OX-BOW LAKES: when meanders erode towards each other they form an ox-bow lake
- the neck of the meander is gradually eroded and then the water now takes the shortest route as the deposition seals off the old meander
- MEANDERS: bends in the river found in lowland areas
- erosion and deposition landforms
- LOWER COURSE: very gentle
- deposition landforms
- FLOODPLAIN : wide, flat areas on either side of a river in its middle and lower course - created by migrating meanders
- LEVEES: form when deposition raises the river bed so the channel can't carry as much water = channel overflows = coarser sediment is deposited on the banks = raising the levees
- ESTUARIES: where the river meets the sea
- deposition landforms
- UPPER COURSE: steep
- CROSS PROFILE: is a cross section of a river valley
- V-SHAPED VALLEY: valley = steep and v-shaped river = narrow, shallow and turbulent
- FLOODPLAIN: - valley = wide and flat floor - river = wider and deeper
- LEVEES: - valley = very wide and flat - river = wide, deep with large sediment load
- changes to the cross profile are mainly due to channel erosion, broadening and flattening the base of the valley
- processes of river erosion
- two types: VERTICAL (downwards) and LATERAL (sideways)
- HYDRAULIC ACTION: force of water hitting the river bed and banks [most effective when water is moving fast and at high volume]
- ABRASION: the load carried by the river hits the bed or banks, dislodging particles
- ATTRITION: stones carried by the river knock against each other, becoming smaller and more rounded
- SOLUTION: alkaline rocks are dissolved by slightly acidic river water
- transportation
- 4 types
- SOLUTION: dissolved load
- SUSPENSION: small river sediment held in the river
- TRACTION: large particles rolled on the riverbed
- SALTATION: bouncing of particles too heavy to be suspended
- the size and amount of load depends on the rivers speed and velocity
- deposition
- when velocity decreases, the river has n o energy to transport its load so it deposits it.
- large rocks ( carried by traction) are carried short distances at high flow & deposited at the upper course
- smaller sediment (carried by suspension) is deposited on a rivers bank or bed where velocity is slow due to friction [middle course]
- lots of deposition occurs at the mouth as there is a gentle gradient [velocity is reduced] [ lower course]
- 4 types
- RIVER TEES [north-east england - source is in the pennine hills]
- [erosion] high force - waterfall and gorge
- [deposition] meanders, levees and floodplains can be found along this river
- FLOODING: occurs when a river can't hold the amount of water flowing in it
- sudden floods are called FLASH FLOODS [ occurs in the summer and are associated with heavy rainstorms]
- after long periods of rainfall - RIVER FLOODS [occurs in the winter]
- FLOOD RISK
- PHYSICAL FACTORS
- PRECIPITATION: torrential rain storms can lead to flooding
- GEOLOGY: impermeable rocks don't let water pass through so it flows overland and into river channels
- RELIEF: steep slopes = water flows quicker into channels
- HUMAN FACTORS
- URBANISATION : impermeable surfaces = water flows quicker into sewers, drains and river channels
- DEFORESTATION: when trees are removed, excess water from the tree will flow rapidly into the river channels
- AGRICULTURE: exposed soil can lead to increased surface runoff
- PHYSICAL FACTORS
- HYDRO GRAPH: shows how a river reacts to a rainfall event
- it shows rainfall and discharge
- LAG TIME: time between peak rainfall and peak discharge [[the shorter the lag time, the greater risk of flooding]]
- FACTORS WHICH AFFECT THE SHAPE: - basin size - drainage density - rock type - land use - relief - soil moisture - rainfall intensity
- MANAGEMENT
- HARD engineering
- DAMS & RESERVOIRS: + regulate river flow + multi-purpose + can store water in reservoir - expensive - often flood large areas of land
- CHANNEL STRAIGHTENING: cutting through meanders creating a straight channel, speeding up water = - increase risk downstream - they are lined with concrete which can be unattractive and damages wildlife
- EMBANKMENTS: raise the level of a river bank allowing channel to hold more water = + cheaper + looks natural + more sustainable
- FLOOD RELIEF CHANNELS: built to by-pass urban areas --- allows excess water to flow into the channel, reducing threat
- CLYWEDOG RESERVOIR: built in the 1960s to help prevent flooding of the river severn - it stretches 10km - fills in the winter and releases in the summer to maintain constant flow
- JUBILEE RIVER, MAIDENHEAD: 11km long flood relief channel built to reduce flood risk - opened in 2002 - positive impact by creating new wetlands
- SOFT engineering
- AFFORESTATION [planting trees] : trees obstruct the flow of water - water is taken up by trees and evaporated from leaves and branches = + cheap
- WETLANDS AND FLOOD STORAGE AREAS : areas which are allowed to flood - this reduces the risk of flooding
- FLOODPLAIN ZONING: puts more useful land further away from the river = + can reduce losses
- RIVER RESTORATION: restore to original course = + uses natural processes and features of a river to slow down flow
- the environment agency produces flood maps and issues flood warning
- flood watch
- flood warning
- severe flood warning
- BANBURY, 50km north of oxford - population of 45000
- CHANGE was needed as: 1998 flood closed the railway station with £12.5 million worth of damage - 2007 flooded again
- FLOOD DEFENCE SYSTEM (2012) : - raised motorway - quality of life improved - scheme cost £18.5 million - over 400 houses and 70 businesses saved - new habitat created
- HARD engineering
- key words
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