rivers Flashcards
type of erosion
attrition / abrasion / hydraulic action / solution
define river discharge
the volume of water passing a point in the river in a set time
types of sediment transportation
saltation / solution / traction / suspension
one benefit of building levees to control river flooding
- cheap to construct so allows large areas to be constructed
- natural appearance limits impact on tourism
one disadvantage of levees
increases risk of flooding downstream
loss of valuable farmland
less effective than hard construction techniques
explain why washlands reduce the risk of flooding somewhere else
excess water floods the washland
therefore rivers discharge is reduced
describe how a meander develops into a lake
meander becomes more pronouns allowing narrow neck to form
rover erodes through neck
water takes the fastest route and by passes the old loop
causes deposition build up at entrances of old channel forming an oxbow lake
explain one way in which rivers transport their load
solution - rock minerals enter water having been chemically dissolved
suspension - when rock particles are small enough to be carried
traction - when rock material is rolled along a river bed in times of high discharge
saltation - when material is partially in suspension and partially bedlam thus ‘jumping’
explain two differences between upper course and lower course river landscapes
- upper course have narrower valleys because discharge is lower - thus less erosion
- lower courses have more meandering because of higher discharge - more lateral erosion
- upper course is irregular and include waterfalls because of lower discharge - less erosion and landscape modification
explain one reason why high discharge can increase erosion
- increased velocity so more abrasion
- increased load - increases abrasion
explain two ways in which human activities can affect hydrographs
more urbanisation - increases rate of surface run off because more impermeable surfaces - affect lag time - increases discharge
deforestation - affects interception rates - changing run off and lag times
for a named river explain why it floods
river seven - antecedent conditions / heavy rainfall - leading to flooding as baneful discharge exceeded
describe how river discharge is calculated
width and depth measured to Gove cross sectional area
cross sectional area multiplied by velocity
to give cumbers - cubic metres per second
explain how a meander is formed
abrasion takes place on outside of bend - because fastest flowing part of channel - slowest - flowing water on inside bend - so deposition occurs there
explain one reason why the antecedent conditions in a drainage basin can affect the peak discharge of a rivers hydrograph
heavy rainfall - ground saturated - can’t take up more water - higher surface run off - smaller lag time and higher peak discharge
explain now way that deposition leads to formation of levees
- levees formed when a river is in flood and bursts its banks- load is deposited along the river bank as the river slows down - layers build up
explain one reason why river velocity increases downstream
channel becomes wider and deeper downstream - reduces the rampant of friction
explain one way channelisation helps manage river landscapes
making channel wider and deeper - increases capacity to hold river water
explain one way that weather and climate can affect river erosion
global climate change - increases amount of evaporation - reduces erosion
intense periods of rainfall - increase erosion
explain how human actions have increased flood risk
river severn - Tewkesbury
- lots of bridging point settlements increasing vulnerability = urbanisation
- damage - 140,000 of damage for local council + 48000 houses damaged
examples of hard engineering strategies
embankments - banks raised to increase channel size
flood walls - increase capacity
flood barriers - stop water flow
channelisation - river channel deepened and widened
dams - built to regulate and control river flow
examples of soft engineering strategies
- washland - parts of the floodplain where flooding is allowed
- afforestation - planting trees so more infiltration and less surface run off
- flood warning system
- lands zoning
explain formation of a flood plain
form due to both erosion and deposition
erosion removes interlocking spurs creating a wide flat area on either side of river
during a flood material being carried is deposited - as river loses energy
overtime height of floodplain increases as layers of deposition build up
explain how a waterfall will change in the future
will retreat - soft rock is easily eroded - by abrasion
