water cycle

hydrosphere

water on or close to the earths surface

97% of this is oceanic water

3% is fresh water which is locked up in land ice,glaciers and permafrost (cryospheric water).groundwater,lakes,soil,wetland,rivers,biomass(terrestial water),and atmospheric water

cryospheric water

the water locked up on earth surface as ice

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 vapor

distribution of earths water

biggest store of water is in the oceans with 97% (27.5 times more than all stores combined

only 2.7% of earths water is fresh water

majprity of fresh water is frozen

more than double all liquid water sttores

greatest liquid fresh water store is groundwater

30x larger than all other fresh water liquid stores

cryosphere

is those portions of the earth’s surface where water is in solid form

• sea ice forms when water in the oceans is cooled to temperatures below freezing

• ice shelves are platforms of ice that form where ice sheets and glaciers move out into the oceans.

• ice sheets-is a mass of glacial land ice extending more than 50,000 km2 - they form in areas where snow that falls in winter does not melt entirely over the summer Over thousands of years the layers of snow pile up into thick masses of ice growing thicker

• ice caps-thick layers of ice on land that are smaller than 50,000km usually found in mountainous areas

• alpine glaciers-thick masses of ice found in deep valleys or upland hollows

• permafrost-defined as ground (soil or rock and included ice or organic material)that remains at or below 0 degrees for at least 2 consecutive years

terrestial water

• surface water is the free-flowing water of rivers as well as the water of ponds and lakes

• rivers act as both a transfer and store of water they are streams of water within a defined channel.

• lakes-collections of fresh water found in hollows on the land surface are generally deemed a lake if they are greater than 2 hectares

• wetlands-areas of marsh,fen,peatland or water

• groundwater(lithosphere)-water that collects underground in the pore spaces of rock

• soil water-is that which is held together by air,in unsaturated upper weathered layers of the earth .it affects runoff potential and flood control

• biological water- the water stores in all the biomass

water table

the depth at which soil pore spaces or fractures and voids in rock become completely saturated with water

atmosphere

most common atmospheric water exists as a gas-water vapor

water vapor is important as it absorbs, reflects, and scatters incoming solar radiation, keeping the atmosphere at a temperature that can maintain life.-cold air cannot hold as much water vapor as warm air(why air over the poles is quite dry whereas air over the tropics is humid

increase in water vapour-increase in atmospheric temperatures(positive feedback as a small increase in global temperature would lead to a rise in global water vapour levels ,thus further enhancing atmospheric warming

evaporation

occurs when energy from solar radiation hits the surface of water or land and casues liquid water to change state from liquid to gas

what controls the rate of this process

• amount of solar energy

• availability of water

• humidity of the air

• temperature of the air

transpiration

where water is transported from the roots of a plant to its leaves and then lost through pores on the leaf surface

leaves can also intercept rain as it falls and this water can be evaporated before it reaches the soil

condensation

as air cools it is able to hold less water vapour.This means that if it is colled sufficiently then it willl get to a temperature at which it becomes saturated(dew point temperature)

excess water in the air will then be converted to liquid water

cryospheric processes

Processes that affect the total mass of ice at any scale from the local patches of frozen ground to global ice amounts. They include accumulation (the build-up of ice mass and reduction in energy) and ablation (the loss of ice mass and increase in energy).

concept of positive feedback within the water cycle

increased rainfall in a drainage basin will increase water in soil stores/surface stores

this will lead to more evaporation and transpiration

increased water vapour

greater potential rainfall

describe the pattern of stores in a global water cycle

ocean is by far the largest store (1000km3)

other stores like freshwater are all much smaller,ranging from atmospheric water at 12.7 to ice at 26,350

there is a very large difference between the largest and other stores

describe the pattern of flow in the global water cycle

ocean has the highest magnitude of flows (precipitation and evaporation)

water vapour has the least magnitude of flows

ocean evaporation has a diffwrence at least 260

what is the relationship between stores and flows in the global water cycle

weak relationship between large stores and large flows (ocean and ocean evapotranspiration)

flows have a small impact on the stores’ long residency time, largest flows impact the largest stores, flows are still relatively small compared to the store

A strong relationship between small stores and small flows (atmosphere and land precipitation)flows are bigger than stores therefore flows have a big impact on the stores, short residency time, flows operating on the land are balanced so the size of land stores doesn’t change over time

drainage basin

is the area that supplies a river with its supply of water, this includes water found below the water table as well as soil water and any surface flow. Drainage basins are separated from another b high land called a watershed

precipitation store

the precipitation that falls on the vegetation surfaces or human-made cover and it is temporarily stored on these surfaces. Intercepted water can be evaporated directly to the atmosphere, absorbed by the canopy surfaces, or ultimately transmitted to the ground surface

stemflow

the portion of precipitation intercepted by the canopy that reaches the ground by flowing down stems ,stalks or tree boles

throughfall

the portion of the precipitation that reaches the ground directly through gaps in the vegetation canopy and drips from leaves,twigs and stems .This occurs when the canopy-surface rainwater storage exceeds its storage capacity

infiltration

the downward movement of water from the surface to soil

overland flow

the tendency of water to flow horizontally across land surfaces when rainfall has exceeded the infiltration capacity of the soil and all surface stores are full to overflowing

throughflow

the movement of water downslope through the subsoil under the influence of gravity. It is particularly effective when underlying permeable rock prevents further downward movement

percolation

the downward movement of water within the rock under the soil surface. Rates vary depending on the nature of the rock

ground water flow

the slow movement of water though underlying rocks

how does a drainage basin operate?

inputs

• precipitation onto land

• precipitation onto sea

stores

• lakes and surface water

• tiver channels

• interception from plants

• soil water

• groundwater

transfers

• overland flow

• channel flow

• throughflow stemflow

• infiltration

• percolation

• throughflow

• groundwater flow

outputs

• evaporation and transpiration from vegetation

• evaporation from water surfaces

• run off from rivers

• evaporation from the sea

impact of temperature on evapotranspiration and the impact that inputs become outputs in a drainage basin

increases evaporation and plant growth this means quick seasonal,reduces all subsequent flows

impact of vegetation density on interception and impact on speed that inputs become outputs in a drainage basin

more vegetation density means a greater extent of vegetation and, a greater potential for interception this slows down the movement of water and encourages infiltration

impact of soil porosity on infiltration

greater the amount of pores the quicker the infiltration this slows subsequent flows even slower

impact of surface type (gradient influences rate of flow) on overland flow

smoother surface the quicker it will move/water travels,fastests flow,water goes straight into main channel

impact of rock porosity on groundwater storage

the more permeable the rocks are,quicker the water is absorbed,slowest flow,long residency time in aquifer

river discharge and the impact of area of drainage basin for scale/amount of rainfall

more drained means more water therefore greater slope angle,greater speed and second fastest flows ,output of systems (cancascade)

water balance

within a drainage basin the balance between inputs and(precipitation) and outputs (runoff,evapotranspiration,soil and groundwater storage)

rivers can only occur if the stores are able to release water ,there is a direct precipitation or there is overland flow into the river,As they move downstream,larger rivers are also fed by their tributary streams

rivers regime

discharge levels often rise and fall,showing an annual pattern

they vary in the short term following a heavy rainfall

water balance equation

precipitation=discharge (Q) + evapotranspiration (E) +- changes in storage(S)

the warmer it is the higher the evapotranspiration,it often happens that the temperature and so and so the atmosphere ability to hold water vapour is greater than the amount of water available.

potential evapotranspiration

is the amount of water that could be evaporated or transpires from an area if there was sufficient water available

the soil moisture graph

the storm flood hydropgraph

a hydrograph is a graph of river discharge against time. A storm hydrograph is the graph of the discharge river leading up to and following a storm or rainfall event(storm flow)

it starts with the base flow. The river is fed by the throughflow of soil water and groundwater. The slow movement of this water means the changes in discharge are small

as storm water enters the drainage basin the river begins to be fed by much more fast-moving water. The discharge rises,

it eventually reaches a peak discharge

(lag time)-the time taken from the peak rainfall to the peak discharge

storm hydropgraph

physical factors

drainage basins that are more circular in shape lead to more flashy hydrographs than those that are long and thin because each point in the drainage basin is roughly equidistant from the measuring point on a river

factors controlling the shappe of the strom hydrograph

• basin size

• basin shape

• basin relief

• soil type

• rock type

• drainage density

basin size

• large basin-water will take longer to reach the channel as it has a longer distance to travel

• small basins-water will reach the channel rapidly as it has a shorter distance to travel (more flashy therefore steeper hydrograph)

basin shape

circular basins-it will take less time for the water to reach the channel as all the extremities are equidistant from the channel (flashy)

elongated basins-water will take longer time to reach the channel from the extremities of the drainage basin

basin relief

steep slopes-water flows repidly downhill and reaches the channel quickly

gentle slopes-water can infiltrate intot he ground and travel slowly to the channel through the soil and rock

soil type

clay soild and thin soils-clay soild have a low porosity and the grains swell when the absorb water so water infiltrates slwoly,thin soils becomes saturated quickly

sandy soils and thick soils-sandy soils have a high porosity so the water can infiltrate.Deep soils allow more infiltration

rock type

permeable rocks-water percolates through pore spaces and fissures into the groundwater store

impermeable rocks-water cannot percolate into the rock causing surface run off to the rivers

drainage density

high drainage density-a large number of surface streams per km2 so the stormwater will reach the main channel rapidly

low drainage density-a small number of surface streams per km2 as the water travels slowly through the soil and rocks to the river

natural vegetation

forest and woodland-incepts water and high rates of evapotranspiration so less water reaches the channel and more slowly

thin grass-incepts little water and there is little loss by evapotranspiration so more water directly reaches the channel rapidly

land use

urban-urban surfaces have more tarmac and drains that carry transport the water rapidly and directly tot the river

rural-vegetates surfaces intercepts water and allow infiltration so water travles slowly to the river channel

climatic factors

precipitation intensity,duration

snowfall

evapotranpiration

prcipitation intensity

high intensity-when rain falls fater than the infiltration capacity surface runoff occurs and transports the water rapidly

low intensity-water can infiltrate to the soils and travels slowly to the river channel

precipitation duration

prolonged-the water table rises and the soil becomes saturated casuing surface runoff which travels rapidly to the river channel

short duration-the water infiltrates into thee soil and travels through the soil into rocks before reahcoin channel

snowfall

slow-the ground thaws with the snow so the met water can infiltrate into the soil and rocks before reaching channel

fast-melt water cannot infiltrate into frozen geound ao it rapdily flow over to the channel

evapotranpiration

high rates of ET-high losses will reduce channel discharge

low rates-fewer losses from the drainage basin system will increase the discharge in the river channel

affects of deforestation on the water cycle

deforestation reduces interception rates allowing rainwater to hit the surface directly. the lack of vegetation roots reduces the infiltration rate into the soil. These both result in rapid overland flow and flashy hydrograph

it also exposes the soil to greater erosion rates, leading to sedimentation of the channel. This reduces the bank full capacity of a river and leads to a greater chance of flooding

affects of agriculture

ploughing breaks up the topsoil and allows greater infiltration, subduing hydrographs

this can be enhanced by contour ploughing where furrows are created that run directly down the slope, then they can act as small stream channels and lead to flashier hydrographs.Ploughing wet soils cause impermeable smears in the subsoil called plough pans. These inhibit percolation producing greater surface flow.

• terracing on hillsides stops the movement of water downhill and subdues hydrographs

• grass crops increase infiltration and lead to subdued hydrographs

• large numbers of animalls in small areas can impact soils leading to overland flows

growth of urban areas affecting water cycle

growth of urban areas and other large impermeable surfaces such as roads produce flashy rivers.This is exacerbated by the very fact that settlements have been built on floodplains.This urban growth leads to the expansion of built up ,impermeable surfaces such as roads,car parks ,shopping centres etc

most settlements are designed to transfer water as quickly as possible away from human activity to the nearest river

asses the human impact on the water cycle

agriculture has the most significant human impact on the water cycle,drives the majority of deforestation

80% of deforestation in the Amazon basin is to clear land for cattle ranching.

responsible for 70% of freshwater use, main cause of abstraction of groundwater

runoff from agriculture is the main source of water pollution,[esciticides and fertilizers, which can cause eutrophication in water stores

urbanization-impact on local places cities have impermeable surfaces and sewerage systems which speed up hydrology. Industry can be the source of worse pollutants than agriculture, although is on a small scale.As cities expand they build on agricultural land causing new land to be cleared

domestic use of water rises due to the population becoming more affluent

human causes of winchester 2014 floods

• river itchen flows through the centre of winchester in multiple channels with several tributaries .Channel heavily engineered in the past

• large expanse of urban area with impermeable tarmac surfaces

• low lying and houses built on flood plain

• due to climate change the risk of flooding may increase as sea levels rise,winter rainfall increases and flash storms become more frequent.This means more people are liekyl to be at risk more often

natural casues of winchester 2014 floods

• winchester is underlain by permeable chalk aquifer at a shallow depth

• the aquifer is capable of absorbing large amounts of rainfall and releasing it slowly over a long period-prolonged flooding

• the chalk aquifer has a buffering effect so that the rivers have a relatively narrow range of flow in a normal year and generally do not flood in response to short-medium duration heavy rainfall

• after prolonged rainfall, the water table in the aquifer can rise to the ground surface leading to groundwater flooding and lasting for several months

• The last floods of winchester were in January 2001 due to groundwater flooding

• January and February had heavy and prolonged rain due to multiple severe depressions causing repeated storms. River kitchen burst its banks and groundwater flooding .75% of a month’s rainfall is expected in 5 days.6 months of rain in just 2 months

economic impacts of winchester 2014 floods

• hampshire county council spent 1.6 milllion on defence after this years floods

• by july 2014 winchester city council had spent £160,000 on repairs to council houses

• temporary disruption to businesses

• the estimated cost to Hampshire county council was £68.5m

socila impacts of winchester floods 2014

• river park leisure centre temporsrily closed

• insurance costs

• distruption to road and rail travel -road closures and train cancellations

• homes flooded,personnel possessions destroyed .Residnets evacuated and temporarily re located

• disruption to education-primary schools and unis disrupted

enviromental impacts of winchester floods 2014

• sewage contamination in homes and parks-water lanes,park avenue and st cross

• tress fell

short term managmwnt of winchester floods 2014

• fire servie brough 2 high volujme pumps-pumpes 84,000 litres of water an hour

• business owners can claim for losses throguh the business rates floodng relief

• sandbaggin in many roads

• road closures at water lane

• homes evacuated ,residents rehoused

long term

• sluice gates control flood levels at durngate at park avenue

• repai and renw grants scheme -residents able to claim as much as 5k as well as claim back on council tax

• spent 1,6 million on defence repairs this years flood

• 70 foot barrier across park avenue ,artificial pond to ease pressure on the city

future plans

planning controls -lower value land use in some risk flood pain locations-playing fields and nature reserve

erecting permanent barriers on water lane ane park avenue-watertight walls made of concrete

upgrade sluice

impacts of human activity on drainage basins

and whether they alter the dynamic or return the system to equilibrium

• urbanisation-hard surfaces such as tarmac roads and pavemtn in our towns casue rain water to run rapidly over land,rather than draining into the ground,thereby increasing the risk of flooding

• population growth-with the growing population and extended dry spells has increased the pressure on water environment

• climate change-this will increase risks associated with abstraction and low flow

• agricultural practices-compacted soils and watercourses which have been physically modified in order to get rainfall out of the sea as fast as possible,also reduce the amount of water that is available to be stores in the catchment

• catchments managemnt-due to kitchen being affordable a high level of enivornemtnel protection,more water is protected from groundwater abstraction

• water storage projects to provide resilient water supplies to the region. it supports reduced abstraction

• abstraction-the kitchen and its tributaries are supplied from groundwater during times of low rainfall

with the reference to river catchment you have studied asses the potential impacts of human activity upon the drainage basin

The River itchen is an example

major activity is urbanisation-impermeable surfaces reduced infiltration and increased runoff-lag time would be short increasing flood risk