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Water cycles, RIVER CULM: case study - Coggle Diagram
Water cycles
Flows
- evaporation 336 (sea)
- precipitation 300 (sea)
- precpitation 100 (land)
- evapotranspiration 64 (land)
- run off 19
- underground flow to ocean 17
flows are the physical mechanisms which drive the flux of material between stores eg evaporation, precipitation, transpiration, runoff etc..
- Fluxes are measurements of the rate of flow of material between the stores. because fluxes are a rate, the units are mass per unit time (100 km3/yr)
Energy in the form of latent heat is either absorbed or released when water changes state.
- Latent heat of vaporisation = condensation and evaporation.
- Latent heat of fusion = freezing and melting
- Latent hea of sublimation = deposition and sublimation.
Evaporation:
- this process increases the amount of water stored in the atmosphere.
- the rate that this process occurs at depends on :
- the amount of solar energy
- surface area and avaliabilty of water
- wind speed
- humidity of the air: the closer the air is to saturation point, the slower the process.
- the temperature of the air; warmer air holds more water vapour than cold air.
- when liquid water changes states into a gas, water vapour. it gains energy.
Condensation:
- this process occurs when water vapour becomes a liquid - it loses energy to the surroundings.
- it occurs when air containing water vapour cools to its dew point eg when temperatures fall at night time due to heat being lost into space.
- dew point the atmospheric temperature below which water droplets begin to condense and dew can form.
- water droplets can stay in the atmospher or flow to other subsystems eg form as a dew on leaves, decreasing the amount of water stored in the atmosphere.
- NB.Temperature has the greatest control on the rate of this process.
- if there's lots of vapour in the atmosphere and temperatures suddenly drop, condensation rates will be higher.
Albation:
- albation is the natural loss of snow or ice from the surface of a glacier, usually by melting but also by calving (breaking off).
- the area of a glacier where the loss of snow and ice is greater than the amount replaced each year is called the Albation Zone.
- Glaciers may retreat and thin
clouds
How do clouds form at a local scale?
- condensation and cloud formationoccurs in the troposphere (0-10km above sea level)
- the troposphere is the lowest portion of the earth's atmosphere, and is also where all weather takes place. it contains 99% of it water vapour.
why does it get cooler as you go up?
- the troposphere is primarily heated from the bottom because the surface is much better at absorbing a wide range of solar radiation as compared to the air.
- the surface is warmed by the sun and then this energy warms the air above the ground through conduction.
- this warm air rises upwards into the troposphere through convection.
- when the air gets cool enough it condenses.
why is there less air pressure as you go up?
- air pressure refers to the weight of the earth's atmosphere pressing down on everything.
- the closer to earth's surface you get the more air is above you pressing down.
- if air rises less pressure is exerted on it and it expands. we can see the same effect happening underwater when a suba diver releases bubbles. they get bigger when they rise.
- Adiabatic expansion - the description of what happens to a parcel of air as itrises as air pressure decreases causeing an increase in volume and a decrease in temperature.
rainfall
- orographic rainfall = when moist air moves over a mountain range, as the air rises. commonly found in coastal regions.
- wind from the sea (highly saturated) hits mountain and forced upwards.
- air mass cools and condenses into clouds. reaches dew point and begings to precipitate on the windward side of the mountain(facing the sea).
- the leeward side (the other side of the mountain gets less rain = less vegitation.
Frontal rainfall:
- when a warm, moist air mass meets a cold, dry air mass,
- 1.the warm air rises and the water vapour from the warm air condenses due to the meeting of cold air.( it rises).
- reaches dew point and then precipitates.
- if a warm front, the warm air will gradually rise causing mild to moderate, prolonged rainfall.
- if it is a cold front then the air will rise rapidly causing unstable weather eg thunderstroms.
- common in UK
Convectional precipitaion:
- on hot days, the sun heats the ground. the ground releases some of the heat which warms the air.
- warm air rises and cools to condense it's water vapour into a liquid.
- instant rainfall without warning.
- relys on the sun, common in tropical regions with a more intense uv and angle to the sun.
The drainage Basin system
- an area of land that is drained by a river and its tributaries.
- fluxes and processes are usually measured and observed at this scale. within a drainage basin, inputs and outputs can be more accurately ascertined. at this scale we can establish a water balance.
the drainage basin is an example of an open system as there are external inputs and outputs.
- this means the amount of water in the drainage basin varies over time (hourly, seasonal, annually)
- can range from very small scal - small stream.
- to very large scale - crossing the borders of countries.
source: springs etc
tributary: small streams that link to the mainstream that flows downhill.
confluence: where the tributary meets the channel
water shed: the edge of the drainage basin
channel
marsh
Factors affecting vertical flows of water through the drainage basin:
interception
- conopy density: the amount of leaf cover. those with less cover experience more throughfall. this is accentuated in temperate climates where trees shed their leaves in the winter season and lie dormant.
tropical rainforests are so dense that they intercept almost 60% of rainfall.
- Leaf structure: studies show needle shaped leaves can be more effective at intercepting rainfall than broadleaved. drip tips on broad leaves will encourage water to fall to the ground.
Infiltration:
-Soil porosity is the most influential factor.
- coarse grained soils will have more pore spaces and therefore more water can pass through.
- roots and burrowing organisms: create micro and macro channels for water to flow through the soil.
- the type of rainfall: prolongues rainfall will saturate the soils. drizzle will cause soil particles to expand, thus reducing the size of the pores etween them.
high-impact raindrops will dislodge soil clumos, break them into smaller pieces and they can clog up pore spaces near the surface.
- porosity
- gradient
- volume of inputs
4.type of precipitation (snow/rain)
The water budget (water balance)
a water budget is an accounting of water movement into and out of, and storage change within, any particular area (eg a drainage basin, a construction site)...
-
equation for calculating the waterbalance:
precipiation = runoff + evapotranspiration + the change in storage( in soil or the bedrock)
- the evapotranspiration depends on dry and high temperatures -> there will be more E
- the air is humid and already holds lots of moisture, the E will be inhibited.
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Aquifers
- an aquifer is an underground layer of water-bearing permeable eg chalk
an artisan aquifer is a confined aquifer containing groundwater under positive pressure; this causes the water level in a well to rise of its own accord to the surface e.g london's artisan basin
Maximum sustainable yield:
the maximum level of extraction of water that can be maintained indefinitely for a given area..
what happens when humans extract more than the maximum sustainable yield?
- groundwater depletion
- saltwater intrusion
- formation of cone of depression in the water table.
textbook notes:
key terms:
- atmospheric water water found in the atmosphere; mainly water vapour with some liquid water (could and rain droplets ) and ice crystals)
- Cyrospheric water the water locked up on the earth's surface as ice.
- discharge the amount of water in a river flowing past a particular point expressed as m3s-1(cumecs).
- greenhouse gas any gaseous compound in the atmosphere that allows short wave ultra violet radiation from the sun to pass through the atmosphere, but then prevents outgoing terrestrial infrared radiation from escaping to space.
- hydrosphere a discontinuous layer of water at or near the earth's surface. it includes all liquid and frozen surface waters, groundwater held in soil and rock and atmospheric water vapour.
- oceanic water the water contained in the earth's oceans and seas but not including such inland seas eg the Caspian Sea.
- terrestrial water this consist of groundwater, soil moisture, lakes, wet lands and rivers.
the major stores of water:
- 97%of the hydrosphere is oceanic water. the 3% is atmospheric and terrestrial water.
- the amount of water in each of these stores is in a state of dynamic equilibrium.
oceanic water
- biggest store of water, 1,320,000,000 - 1,370,000,000km3 with an average depth of 3,682m.
- covers 72% of the earth's surface.
- salty taste as it contains dissolved salts. the salts allow it to stay liquid water below 0degrees. they are alkaline with an average ph of 8.14. In the last 250 years the ph has fallen to 8.25. this is linked to the increase of atmospheric carbon.
the cyrosphere
- water in solid form.
- sea ice
- Atlantic Ocean ice grows in winter and shrinks in summer.
- waters around Antarctica are also solid.
- when it melts, there isn't a transgression as it forms from the ocean itself.
- Ice sheets
- platforms of ice where ice sheets and glaciers move out into the oceans.
- ice shelves
- Antarctica and greenland. Arctic and Canada and Alaska.
- icebergs break off glaciers and ice shelves.
- they raise sea level only when they leave the land and push into the water, but not when they melt into the water. (it displaces the water)
- ice sheets (Greenland and antarctic) contain 99% of earth's fresh water ice on earth.
- ice caps are thick layers of ice on land that are usually smaller than 50,000km2. found in mountainous areas. they are dome shaped and are centred over the highest point of an upland area, flow outwards
- permafrost is defined as ground that remains at or below 0 degrees for at least 2 years. can be >1500m thick. most of it formed during the last glacial period. can contain Methane.
terrestrial water
- surface water
- rivers, ponds and lakes.
- rivers are a store and transfer of water.
- lakes are collections of fresh water found in hollows on the land. greater than 2hectacres. below this they are a pond. most lakes are in the northern hemisphere at higher latitudes. the largest lake is the Caspian Sea 78,200 km3.
- wet lands are marsh areas, peat and saturated soils.
groundwater (lithosphere)
- water that collects underground. 4,000m
- borehole 13km found huge quantities of hot mineralized water (russia).
- when the rock/soil becomes completely saturated this is known as the water table.
- natural discharge of groundwater = springs and seeps. they form oasis' and wetlands.
- groundwater is rapidly reducing due to extensive extraction from wells and bore holes.
soil water
- water that is held together with air in unsaturated upper weathered layers of the earth.
- it affects climate and weather. Run-off potential and flood control, soil erosion, slope failure , resevoir management, geotechnical engineering and water quality.
biological water
- all the water stored in biomass, varies from place to place with vegitation dispersion. -> rainforests have higher store of water than a desert.
- the role of animals as a water store is minimal.
- trees keep their store in their roots. it is then transported and stored in the trunk and branches. water is lost through transpiration, water goes throught the stomata in the leaves.
- this storage helos form a resevoir for maintaining climatic environments.
- if vegetation is destroyed, the water store is lost to the atmosphere and the climate will become more desert-like.
Atmospheric water
- stored as water vapour (gas), it is clear, colourless and odourless so we take its presence for granted.
- it absorbs, reflects and scatters incoming solar radiation -> keeping the global temperature stable for life to thrive.
- cold air cannot hold as much water vapour as warm air. -> tropics are very humid and poles are dry.
- a small increase of water vapour will increase the atmospheric temperature (vice versa). this becomes positive feedback
- Clouds are visable mass of water droplets (liquid) or ice crystals (solid) suspended in the air.
- cloud formation is a result of lower layers of the air becoming saturated due to:
- the cooling of air
- and the increase of the water vapour content.
stores
- oceans 1400,000 km3
- ice and snow 27300 km3
- underground water 22900 km3
- lakes 176 km3
- soil moisture 16 km3
- atmosphere 13 km3
- plants and animals and rivers 2 km3
are stores of water evenly distributed around the planet?
- no
- less than 10 countries possess 60%of the world's avaliable freshwater supply.
- 30% of all fresh water is stroed in aquifers. common in chalk, liestone, and sandstone (highly permeable)
Residence times:
- ice caps 15,000 years
- groundwater 10,000
- oceans 3,600
- rivers and lakes 2 weeks -10 years (50 years on a large scale).
- soil moisture 2-50 weeks
- atmospheric water 10 days.
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