Freshwater Flashcards
What are the inputs of a drainage basin?
Precipitation of varying type and intensity
What are the processes of a drainage basin?
Interception surface runoff infiltration throughflow percolation groundwater overland flow base flow vegetation soil cryosphere aquifers
What are the outputs of a drainage basin?
evapotranspiration
river runoff
What is discharge?
the volume of water that passes through a cross section per unit of time
what is occupied channel width?
the distance across the actual channel measured at the water surface; it increases because of input from tributaries etc.
what is channel depth?
the height from the water surface to the stream/river bed channel depth - increases further downstream along with the size of the river. A line connecting all places of greatest depth all along the river is called the ‘thalweg’
what is average velocity?
the speed of the water flow (distance travelled per unit of time),
- it increases steadily further downstream
- further downstream, the river becomes more efficient with proportionally less contact with its bed and banks
what is load quantity?
the capacity of the river including the river load and it increases with large discharge and velocity.
- load particle size decreases considerably downstream and the more angular pebbles become more rounded due to attrition.
what is channel bed roughness?
a measure of how rough the bed of a river is. It decreases significantly downstream because of fewer and smaller stones, this is due to erosion.
- channel bed roughness decreasing allows much faster water flow.
What is the slope angle (gradient)?
How steep the river is.
- The gradient decreases downstream
What is hydraulic radius?
The efficiency of a stream’s shape is measured by its hydraulic radius (the cross sectional area divided by the wetted perimeter.
- the higher the ratio, the more efficient the stream is and the smaller the friction loss is.
what is cross sectional area?
the area of water in a channel cross section multiplied by the average velocity of the water in that cross section
What is abrasion or corrasion?
the wearing away of the bed and bank by the load carried by a river
what is attrition?
the wearing away of the load carried by a river = smaller, rounder particles
what is hydraulic action?
the force of the air and water on the sides of rivers and in cracks
solution or corrosion
the removal of chemical ions, especially calcium, which causes rocks to dissolve
what are the factors affecting erosion?
load velocity and discharge gradient geology pH human impact seasonality
how does load affect erosion?
the heavier and sharper the load, the greater potential for erosion
how do velocity and discharge affect erosion?
the greater the velocity and discharge, the greater the potential for erosion
how does gradient affect erosion?
increased gradient, increases the rate of erosion because of faster speeds.
how does geology affect erosion?
soft, unconsolidated rock, such as sand and gravel are easily eroded.
how does the pH of water affect erosion?
rates of solution are increased when the water is more acidic
how does human activity affect erosion?
deforestation, dams, and bridges interfere with the natural flow of the river and frequently end up increasing the rate of erosion
how does seasonality affect erosion?
more precipitation during rainy/monsoon seasons leads to a faster rate of erosion
what are the different types of transportation?
suspension saltation solution traction flotation
what is suspension?
small particles are held up by turbulent flow in the river
what is saltation?
heavier particles are bounded or bumped along the bed of the river
what is solution?
the chemical load is dissolved in the water
what is traction?
the heaviest material is dragged or rolled along the bed of the river
what is flotation?
leaves and twigs are carried on the surface of the river
what is deposition?
- when a river deposits its load as it slows down and loses its energy
- typically occurs as a river floods across a floodplain, enters the seas, or behind a dam
- it is more likely during low flood conditions (such as drought) than during high flow (flood) conditions - as long as the river is carrying sediment
- the larger, heavier particles are deposited first, the smaller lighter ones later
what are the features of deposition?
floodplains, levees, deltas
what is the formation of a waterfall?
- occur frequently on horizontally bedded rocks
- the soft rock is undercut by hydraulic action and abrasion
- the weight of the water and the lack of support cause the waterfall to collapse and retreat
- over thousands of years, the waterfall may retreat enough to form a steep sided gorge
how are floodplains formed?
through deposition that occurs in the lower parts of the river when it floods
what is the formation of a levee?
- when a river floods, its speed is reduced, slowed down by friction caused by contact with the floodplain
- as its velocity is reduced, the river has to deposit some of its load
- it drops the coarser, heavier material first to form levees at the edge of the river
- this means that over centuries the levees are built up of coarse material such as sand and gravel while the floodplain consists of fine silt and clay.
what is the formation of a meander?
meander development occurs in conditions where channel slope, discharge and load combine to create a situation where meandering is the only way that the stream can use up the energy it possesses equally throughout the channel reach
how are deltas formed?
- formed as river sediments are deposited when a river enters a standing body of water such as a lake, lagoon, ocean.
- deposition occurs because water velocity is reduced
what are the factors affecting the formation of deltas?
- the amount and size of a load:
rivers must be heavily laden, and coarse sediments will be deposited first - salinity
salt water causes clay particles to stick together, they get heavier and are deposited - gradient of coastline
delta formation is more likely on gentle coastlines - vegetation
plant waters will slow waters and so increase deposition - low energy river discharge and/or low energy wave or tidal energy
what are the 3 forms of deltas?
- arcuate
- cuspate
- Bird’s foot
what is an arcuate?
many distributaries which branch out radically
- e.g. Nile Delta
what is a cuspate?
a pointed delta formed by a dominant channel
what is a bird’s foot?
long, projective fingers which grow at the end of distributaries
- e.g. Mississippi Delta
what is lag time?
the time interval between peak rainfall and peak discharge. It is influenced by basin shape, steepness and stream order.
what factors affect peak discharge?
- higher in larger basins
- steep catchments will have lower infiltration rates
- flat catchments will have higher infiltration rates, so more throughflow and lower peaks
what is base flow?
the seepage of groundwater into the channel.
- this can be very important where rocks have high pore spaces.
- baseflow is a slow movement and is the main, long term supplier of the river’s discharge.
what is the recessional limb influenced by?
- basin size
- geological composition
- behaviour of basin size
what is the run-off curve?
reveals the relationship between overland flow and throughflow.
where infiltration is low, high antecedent moisture, impermeable surface and rainfall strong overland flow will dominate.
what are the natural factors influencing hydrographs?
- climate
more total rain = easier to reach total discharge and flood - soils
E.g. impermeable clay soils create more flooding and vice versa - infiltration capacity
soils with low infiltration capacity cause more overland flow = reaches peak discharge faster - rock type
permeable rocks = water infiltrates = reducing the flood peak - drainage density
the more stream channels there are the more water that gets into rivers
what are the natural/man-made factors influencing hydrographs?
- vegetation
intercepts rainfall and so flooding is less likely as it increases lag time - slope angle
on steeper slopes = greater runoff = shorter lag time
what are the man-made factors influencing hydrographs?
- afforestation/deforestation schemes
afforestation = increases infiltration = reduces chance of reaching peak discharge whilst deforestation decreases it. - urbanisation
more impermeable surfaces in built up areas increases runoff into fields - discordant ploughing
causes water to reach the river quicker as the water flows straight to the river through furrows
what are the physical causes of flooding?
- impermeable bedrocks = rainwater cannot soak into the rocks = surface runoff
- sudden rise in temperature = rapid thaw = more water into river
- long periods of hot, dry weather = very hard and compact soil = water cannot soak in = more surface runoff
- during a cloudburst in a thunderstorm, the rain droplets are so large and fall so quickly = no time for the water to sink into the ground so more surface runoff into the river
- steep valley slopes = rainwater enters river channel sooner = the river channel reaches capacity much more quickly
- large amounts of prolonged rainfall = water saturates the ground = won’t be absorbed anymore thus it will flow more quickly overland as surface runoff into the river
what are the human causes of flooding?
- ploughing up and down slopes = channels the rainwater to the river faster. = more water channelled straight into the river
- deforestation = there is less interception and water will move to the river more quickly
- dams may burst which will cause excess water in river channels and flooding of large areas
- if there is a town on a floodplain, storm drains will allow water to move into the river at a greater speed and so make flooding more likely
- urbanisation = impermeable ground and storm drains collect rainfall and channel it straight into a river or a stream
- increased building of impermeable surfaces like tarmac means increased surface runoff and this therefore increases river discharge.
define prediction
using previous experiences and data to estimate the outcomes of the future
what is weather forecasting?
the application of science and technology to predict the conditions of the atmosphere for a given location and time
what is climate modelling?
computer simulations that incorporate both theory and direct observations of the past and present in order to project climate into the future
what is a limitation of climate modelling?
limitations still exist such as the inability to predict a flash flood event and the constantly changing landscape caused by human intervention
what are the ways to improve flood warnings?
- improve rainfall and snowpack estimates, better and longer forecasts of rainfall
- become better at gauging rivers, collecting meteorological info and mapping channels
- become better and update info about human populations, infrastructure, elevation
- stream channels need to be incorporated into flood risk assessment models
- become better at sharing info between forecasters, national agencies, relief organisations and the general public
- technology should be shared among all agencies involved in flood forecasting (even with international drainage basins)
what are the structural measures of flood mitigation?
flood abatement which decreases the amount of runoff, thereby reduces the flood peak in a drainage basin
what are the examples of flood abatement?
- reforestation/afforestation = increases interception and evaporation
- treatment of slopes such as contour ploughing or terracing to reduce runoff
- construction of small water and sediment holding areas like dams that can hold water and reduce total volume of water in the river at one moment
- preservation of natural water storage zones like lakes
- channel modification - making it deeper so can hold more water and doesn’t run as fast.
- levee strengthening = build up levees to increase total volume river can hold until peak discharge
what are the planning methods for flood mitigation?
- personal insurance
- flood preparation
- flood warning technology
what is personal insurance?
- loss sharing adjustments include disaster aid and insurance
- disaster aid = any aid such as money, equipment, staff and technical assistant that are given to a community following a disaster
- in developed countries, insurance is an important loss-sharing strategy
- however, not all flood-prone households have insurance and many of those that are insured may be underinsured
- its lack of availability in many poor countries makes it of limited use
what goes into flood preparation?
- emergency measures = removal of people and property
- having flood-fighting techniques at the ready i.e. sandbags
- flood proofing = sealing walls, sewer adjustments by the use of valves, covering buildings and machinery, having wall sockets high up on the wall
what are two examples of flood warning technology?
- Bhutan’s early warning systems
- Japan’s underground tunnels and education programmes
what is physical water scarcity?
when there is not enough water to meet both human demands and those of ecosystems to function effectively.
where does physical water scarcity typically occur?
- arid regions frequently suffer from physical water scarcity
- places where water seems abundant but resources are over-committed
- exception: Dubai = physical water scarcity but not suffering because they can afford technology i.e desalination
what is economic water scarcity?
caused by lack of investment in water infrastructure. Where a country physically has sufficient water to meet its needs but requires additional storage and transport facilities. This means embarking on large and expensive water development projects.
what is a cause of water scarcity?
drought which is a prolonged period of time with lower than expected rainfall
what are the natural causes of drought?
- land and water temperatures cause drought. As temps increase, more water evaporates
- air circulation and weather patterns also cause drought. Key events like El Nino or La Nina help contribute to drought in areas
- soil moisture levels also contribute to drought. when soil moisture is depleted there is less evaporation of water to create clouds. surface temperatures rise, more water is needed and less is available which contributes to a more severe drought.
what are the human causes of drought?
- drought can be a supply and demand of water issue. when a region is growing rapidly, the demand for water can exceed the supply. excessive irrigation is an example of people contributing to a drought.
- if the timing of water doesn’t match the agricultural season. you may have too much water when you don’t need it and too little when you do need it. proper storage and collection of water is key to counter balancing this cycle and clearly in the scope of human management.
what are the economic impacts of drought?
- farmers may lose money if a drought destroys their crops.
- people may have to pay more for food
- power companies that normally rely on hydroelectric power may have to spend more money on other fuel sources if drought dries up too much of the water supply. The power companies’ customers will also have to pay more.
what are the environmental impacts of drought?
- losses or destruction of fish and wildlife habitat
- lack of food and drinking water for wild animals
- migration of wildlife
- increased stress on endangered species or even extinction
- more wildfires
- wind and water erosion of soils
what are the social impacts of drought?
- anxiety or depression about economic losses caused by drought
- health problems related to low water flows and poor water quality
- health problems related to dust
- loss of human life
- threat to public safety from an increased number of forest and range fires
- reduced incomes
- people may have to move from farms into cities, or from one city to another
- fewer recreational activities
what affects water quantity?
- the amount of evaporation that takes place
- the amount of precipitation that occurs
what is water stress?
- refers to the ability, or lack thereof, to meet human and ecological demand for water
- compared to scarcity, “water stress” is a more inclusive and broader concept. It considers several physical aspects related to water resources, including water scarcity and also water quality, environmental flows, and the accessibility of water.
what is water quality?
refers to the chemical, physical, biological and radiological characteristics of water.
- water related diseases cause 3.4 million deaths each year.
what causes eutrophication?
- surface runoff leads to excess fertilizers like nitrates seeping into the river, causing a nutrient enrichment.
- this causes an algal bloom in the river until eventually, the growing algae blocks out the sun from penetrating the river surface.
- the river becomes anoxic as the bacteria population grow in response to the extra algae.
- the river wildlife can no longer survive and the river becomes a “dead zone”
how do we deal with eutrophication?
- alter human activities to reduce reliance on fertilizers
- regulate and reduce pollutants at the point of emission
i. e. sewage treatment plants that remove nitrates and and phosphate waste. - restore water quality by pumping mud from eutrophic lakes.
what are the two environmental consequences of agricultural activities on water quality?
eutrophication and salinisation
what is salinisation?
- when groundwater levels are close to the surface and is very concentrated with salts.
what can intensify salinisation?
- irrigation can exacerbate salinisation by drawing on water and bringing it closer to the surface.
- capillary forces bring water to the surface where it may evaporate, leaving behind any soluble salts that it is carrying.
- some irrigation, especially paddy rice, requires a lot of water. As it evaporates, the salinity levels of remaining water increases.
- this also occurs behind large dams
what are the effects of salinisation?
- salinisation results in dehydration of plants, causing yield decline or even death.
- crop yield losses may occur even though the effects of salinity may not be obvious
- the salt tolerance of a specific crop depends on its ability to extract water from salinized soils
Apart from exacerbating salinisation, what other impacts does irrigation cause?
- decreases the world’s albedo by replacing reflective sandy spaces with dark green crops
- cause changes in precipitation
Large scale irrigation areas have been linked to increased rainfall, hailstorms, and precipitation. This is because evapotranspiration rates increase.
What is the effect of population and economic growth on aquifers?
- as populations grow, pressure on water resources increases.
- population growth is uneven so there is increased pressure only in certain areas. i.e. urban areas experiencing rapid economic growth are likely to face the greatest increases in water stress.
- leads to aquifers being depleted quickly
what is the effect of pollution on lakes?
- lakes may be polluted by runoff from chemical fertilisers, phosphates, sewage, oil, acidification and industrial effluent.
- this can lead to eutrophication
what are the different techniques to improve water management?
- pricing
- rationing
- desalination
- rain harvesting
- new technology (including irrigation)
- purification
- zoning (nitrate use)
what is an example of pricing and how does it work and what does it affect?
- Australia: Citizens are charged exuberant prices for water.
- metering water: (charging water by volume) makes people realise how much water they are consuming.
- this causes people to treat water with value as it is now costing them money.
- Affects: quality and quantity
- money from the pricing goes into quality, but the price limits the quantity
what is an example of rationing and how does it work and what does it affect?
- Cape Town: They forced agricultural water use use to be reduced by 60% and have designated specific times on a specific day where citizens are allowed to water their gardens.
- Affects: quantity
Limits on water usage per person - E.g. Currently, you can only shower for 30 seconds without having to pay exuberant fees.
- Per fill at water taps, people can only take 25 litres.
what is an example of desalination and how does it work and what does it affect?
- UAE: Locals were first made to pay for water in 2012, and when this happened, water consumption halved
- Affects: Quantity and Quality
- Removes salt from the seawater to make it safe to drink
- Desalination plants are installed, even though these costs quite a lot of money
- they are quite a long term solution so countries with enough money to install them benefit from these.
what is an example of rain harvesting and how does it work and what does it affect?
- UK: Has a growing importance as collecting water in large tanks for non-hygienic uses like watering gardens and flushing the toilet
- Affects: Quantity
- Rainwater is very clean naturally occurring water, and harvesting it before evaporation and contamination happens is rain water harvesting.
- rainwater harvesting systems provide distributed storm and water runoff containment while simultaneously storing water which can be used for irrigation, flushing toilets etc.
- water is generally collected from cleaned roofs, where it runs down a gutter into a storage tank
what is an example of new technology (including irrigation) and how does it work and what does it affect?
- UAE: An alternative method to sprinklers
- Affects: Quantity
- Targeted irrigation no more spraying it everywhere
what is an example of purification and how does it work and what does it affect?
- Africa: Lifestraw technology
- Affects: Quality
- Works off the removal of contaminants from raw water to produce drinking water that is pure enough for human consumption or for industrial use.
- Types of substances that are removed: parasites, bacteria, algae, viruses, fungi, toxic minerals etc.
what is an example of zoning (nitrate use) and how does it work and what does it affect?
- strict laws in the UK and US to where you can and can’t apply nitrates to the land
- Affects: Quality
what are the main aims of IDBM plans?
- IDBM plans aim to deliver sustainable use of the world’s limited freshwater resources
- it uses basin-wide framework for water management that is economically, socially and environmentally sustainable.
- it is not always possible, especially when neighbouring countries are in conflict with each other
what is the Ramsar Convention?
- An international agreement for the protection of wetlands
- it has been recognised that wetlands are important
- the convention was developed and adopted by participating nations at a meeting in Ramsar in 1971
- countries have voluntarily signed up to protect their wetlands, and some are even restoring their wetland areas
- it was developed and adopted by participating nations in Ramsar february 2nd, 1971 and came into force december 21st, 1975
- the Ramsar List of Wetlands of International Important now includes 1,888 sites
- The Ramsar convention classifies wetlands as either marine, coastal, inland or artificial
what causes the loss and degradation of wetlands?
- increased demand for agricultural land
- population growth (increased demand for home development)
- Infrastructure development
- River flow regulation
- Invasion of non native species and pollution (disrupts it as an ecosystem)
- Natural causes such as drought and hurricanes (changes salinity and damages vegetation)
Outline one reason why interception decreases over time during the rainfall event shown in
the diagram.
There is a limit to how much water can be stored on leaf surfaces / on vegetation and after a few hours of rainfall no more interception storage can occur.
Explain five possible ways in which urban development might change how rainwater
moves through a drainage basin
Urbanization would remove vegetation and thus interception storage; as a result, more rain will flow through the drainage basin.
May be more surface storage, as rainwater cannot drain away due to impermeable
surfaces.
Little infiltration of rainfall due to impervious concrete surfaces, increasing run-off
Small soil storage, as little rainwater will filter downwards from the surface.
Altered overland flow of rainfall due to drainage channels and gutters.
