4 Flashcards
drainage basin
area of land where precipitation drains downhill into a body of water
watershed
imaginary line defining boundary of a river drainage basin, separating it from adjacent ones
the hydrological cycle (drainage basin)
1) input - precipitation
2) transfers - throughflow, surface run off, base flow, infiltration, percolation, groundwater flow
3) stores - cryosphere, vegetation, soil, aquifers
4) outputs - evaporation, transpiration (evapotranspiration)
precipitation
primary input into drainage basin, all forms of rainfall, snow, frost…
transfers
1) infiltration - water soaks into soil. vegetation increases inflitration bcs slows down speed at which rainfall arrives at surface
2) surface run off - water flows over land sufrace
3) throughflow - water flowing through soil in natural pipes
4) percolation - vertical movement of water into permeable rocks
5) baseflow – part of a rivers flow that is sustained primarily by groundwater seeping into riverbed
6) groundwater flow – movement of water through permeable rocks
evaporation
process by which liquid or solid changes into a gas (in case of outputs its water vapour)
what affects evaporation
temperature
humidity
surface color (albedo)
evapotranspiration
combined effects of evaporation and transpiration
transpiration – water vapour escapes from living plants
transpiration
water vapour escapes from living plants
water budget
annual balance between inputs and outputs
river discharge
volume of water passing a given point over a set time in cumecs
A of cross section * velocity
discharge formula
A of cross section * velocity
river channel characteristics downstream
1 discharge increases (more tributaries)
2 width increases (more tributaries)
3 depth increases (more water)
4 velocity increases
5 channel bed roughness decreases
6 load quantity increases (material smaller bcs erosion)
7 load particle size decreases
8 slope angle decreases
9 hydraulic radiues
what affects stream flow
1 gravity
2 frictional resistance w bed and banks
conditions for turbulent flow
1 complex channel shapes
2 high velocities
why is velocity distributed unevenly in stream
bcs friction
consequence of friction in stream
uneven distribution of velocity
what does velocity vary with (several stuff)
1 water volume
2 bed roughness
3 gradient
4 width
5 depth
6 channel shape
what + how measures a stream efficiency
measured by the streams hydraulic radius = A cross section/wetted perimeter
the higher the ratio, the smaller the frictional loss, the more efficient the stream
hydraulic radius formula + what does it do
A cross section/wetted perimeter
measures efficiency of stream (the higher the ratio, the smaller the frictional loss, the more efficient the stream)
what causes friction in a stream
bed irregularities, vegetation, trees, contact w bed and banks
name the fluvial processes
erosion, transportation, deposition
when does surface runoff occur
1 precipitation exceeds infiltration rate
2 soil is saturated – pore spaces filled with water
common in areas where precipitation intensity is high and infiltration capacity is low
throughflow
water flowing through soil in natural pipes
baseflow
part of a rivers flow that is sustained primarily by groundwater seeping into riverbed
groundwater flow
movement of water through permeable rocks
infiltration influenced by
1 duration of rainfall
2 soil moisture
3 soil porosity
4 vegetation cover
5 slope angle
infiltration
process where water soaks into soil
infiltration capacity
max rate at which rain can be absorbed by soil
stores
1) vegetation interception - water is caught and stored by vegetation
2) stemflow - water trickles along branches and down main trunk
3) soil
4) aquifers - body of rock/sediment that holds groundwater
5) cryosphere
watertable
upper layer of permanently saturated zone within rocks or sediments
why are aquifers important
they maintain stream flow during dry periods
when does groundwater recharge happen
groundwater – water that percolates into rock beneath soil
1 infiltration from precipitation
2 artificially from irrigation
3 groundwater leakage from adjacent aquifers
soil moisture
subsurface water in soil
field capacity
amount of water held in soil after excess water drains away
confluence
where a stream meets river
where are floodplains useful
agriculture
groundwater
water that percolates into rock beneath soil
percolation
vertical movement of water into permeable rocks
water budget
annual balance between inputs and outputs
river discharge
volume of water at a given point over set time
river erosion
wearing away of land as water flows past bed and banks
types of river erosion
1 hydraulic action - force of air + water into cracks in river bed + banks
2 attrition - load wears away as rocks knock on each other
3 abrasion - rocks smash against bed and banks
4 solution - water w high level of acidity dissolves rocks
what affects erosion
1 load – heavy + angular = more erosion
2 ph level – more acidic level = more solution
3 human impact
4 velocity
types of transportation
1 traction - large rocks roll along bed
2 saltation - small rocks hop along bed
3 suspension - load is light enough to flow along near surface
4 solution - after rocks dissolve little particles remain and keep flowing down
deposition
river loses velocity and therefore drops its load
why does deposition take place
1 decreasing volume of water
2 decreasing gradient
3 increase in friction
levee
landform of deposition – raised banks, formed by repeated flooding
describe levee formation
when river floods, its E is reduced. coarse material is dropped first, then lighter material
delta
formed when stream flows into large body of water – the reduction in river velocity upon meeting a body of water leads to sediment deposition. the sediment builds up, creating this landform
waterfall formation process
soft rock is undercut by hydraulic action + abrasion. weight of water + lack of support leads to plunge pool. overhanging hard rock will eventually collapse
main causes of meander formation
erosion and deposition
floodplains + describe formation
areas of low relief formed by deposition when a river floods
smallest sediment deposited in layers, which build up after each flood, creating fertile floodplains (often used in agriculture)
what does a flood hydrograph do
compares the rainfall received to the river discharge
most important in a flood hydrograph
lag time - difference between peak rainfall and peak discharge
geology influence on flood hydrograph
impermeable rocks will generate more overland flow => shorter lag time + higher peak flow
when does a flood occur
when river can no longer contain all the water it is transporting in its channel. water flows out onto a flood plain
physical factors affecting flood risk
1 precipitation type + intensity
2 temp + evapotranspiration (high temp = faster evaporation)
3 drainage density: high density = many streams = quick water transfer = floods
4 impermeability of rocks and soils
5 slopes (gentle slopes allow for more infiltration)
human factors affecting flood risk
1 urbanisation
2 deforestation
3 channel modification
river regime
shows the pattern of seasonal variation in river discharge over a year
stuff like amount and nature of precipitation, seasonal variations in temp => evapotranspiration, changes in vegetation cover
bankfull discharge
height at which flood could occur
how does urbanisation increase floods
impermeable surfaces, removal of trees, increased drainage density bcs of sewage, bridge supports etc reduce carrying capacity
types of channel modification, how they increase floods
1 channelization – creates new channels, which are likely to be quite straight => increased velocity
2 straightening – increased velocity (higher flood risk downstream)
3 enlargement – through levees – increased amount of water carried, however vulnerable to large scale floods
4 scouring – removes sediment from river bed, allowing it to carry more water (excessive scouring can weaken riverbanks and lead to their collapse)
scouring
removing sediment from river bed, allowing it to carry more water
flood mitigation two main types
hard engineering - building structures, changing the river
soft engineering - natural processes of the river
flood mitigation strategies
dams
channel modification
afforestation
planning???
dams
hold back water during times of flood and release it when flood risk is gone
good bcs water released in a controlled way, + agriculture + hydroelectric power
bad bcs expensive + channel erosion, loss of water bcs evaporation
river engineering
raising banks, straightening, channelization
good bcs river carries more water and this alters the river course
bad bcs higher risk of flooding downstream + expensive
afforestation
good bcs higher interception of rainfall and more or less low cost
bad bcs not always for urbanised areas and floods can still occur, young tress dont do much, most trees lose leaves in the winter which reduces interception
managed flooding
river floods in places other than settlements
bad bcs smaller settlements still flooded
how to improve flood prediction
1 better collection of meteorological info
2 mapping of channels
3 better sharing info between forecasters, countries, general public
factors to physical water scarcity
1 population growth
2 water availability
3 precipitation level
4 demand for water
economic water scarcity
when theres enough water to meet demand but theres a need for additional storage + transportation
factors to economic water scarcity
1 poor management of water resources
2 poverty (poor spend larger proportion of their income on water than families in industrialised nations)
3 lack of water infrastructure
drought is caused by:
1 changes in atmospheric circulation (el nino)
2 less precipitation
3 high temp = more evaporation
severity of drought depends on
1 length of drought
2 how severe water shortage is
impacts of drought
1 less croup yields
2 animal mortality
3 diseases (bcs dehydration)
4 forest fires (bcs vegetation is dry)
5 conflicts over water supply
what affects water quantity
1 precipitation
2 groundwater + river flows
3 use of water by plants
4 evaporation
water stress
occurs when per capita water supply is less than 1700 m cubic per year
impacts of our water use
1 half of wetlands gone
2 freshwater species going extinct
3 many important aquifers being depleted
4 water tables falling at an alarming rate
what affects water quality
1 organic waste from sewage
2 fertilizers from farming
3 heavy metals + acids from industrial processes + transport
what is the largest user of water
agriculture
factors affecting access to safe drinking water
1 water availability
2 water infrastructure
3 cost of water
eutrophication
caused by increased amounts of nitrogen + phosphorus that are carried into streams, causing nutrient enrichment
consequences of eutrophication
1 causes excessive growth of algae
2 loss of fertilizer = economic loss
3 affects human health
4 growth of algae leads to formation of dead zones – areas w no oxygen, leading to organisms dying
how to deal w eutrophication
1 altering human activities that produce pollution, for example alternative types of fertiliser
2 reducing pollutants at point of emission – like sewage treatment plants that remove nitrates + phosphates from waste
how to reduce nitrate loss
1 avoid use of nitrogen fertilisers when soils are wet (to decrease likeliness of soil washing through)
2 preferring crops that conserve nitrogen in the soil
3 avoid applying nitrogen to fields near streams
4 avoid applying nitrogen to fields just before a heavy rain is forecast
stakeholders in eutrophication (dont list just explain)
those who benefit from more crop yields and suffer from eutrophication – who should pay to clean it up??
stakeholders in eutrophication (list)
1 farmers who apply fertilizer
2 chemical companies profiting from fertilizer sale
3 gov that may begin to achieve food security
4 customers who receive more reliable food
5 water companies
impacts of irrigation
1 loss of aquifer capacity – if groundwater is pumped faster than it can be recharged
2 raise the watertable and cause salinization
3 decrease albedo
4 changes in precipitation bcs when irrigated, soils have more moist + vegetation cover => evapotranspiration rates increase
how does irrigation increase precipitation
when irrigated, soils have more moist + vegetation cover => evapotranspiration rates increase
salinisation
increase of amount of salt in soil, which occurs when groundwater levels are close to the surface
capillary forces bring water to surface where it is evaporated, leaving behind salts that can make land toxic to crops
approaches to water management
1 water saving – less bath water, water efficient showers, taps that automatically turn off…
2 customer pricing – charge customers for amount of water they use
3 new tech – desalinisation, intelligent irrigation, monitoring leaks
4 zoning – zones that are protected from development to safeguard water quality. aim – to allow aquifers to recharge
5 rainwater harvesting – capturing and making use of rainfall before it drains away
6 water purification – removal of impurities from water so that its fit for purpose
zoning
zones that are protected from development to safeguard water quality. aim – to allow aquifers to recharge
rainwater harvesting
capturing and making use of rainfall before it drains away
integrated river basin management
method of organizing the protection, management, and development of the resources in a river basin to optimize the benefits from them in a fair way, while also protecting ecosystems
6 concerns in relation to water availability
1 ecosystems
2 flood control
3 transportation
4 water supply
5 economy
6 recreation
wetland
land w permanently flooded soils
threats to wetlands from humans
1 clearance for housing, agriculture etc
2 global warming (sea level rise, drought)
3 mining for coal etc
natural threats to wetlands
1 sea level rise
2 drought
3 hurricanes
benefits from wetlands
1 water storage
2 groundwater recharge
3 erosion control
4 retention of nutrients
5 fishing
