🔵Water Cycle Flashcards
What drives change in a water cycle
Inputs,outputs, flows and stores.
- changes in these have impacts of varying magnitudes over different lengths of time
Water cycle inputs
Precipitation
What are the 3 main types if rainfall
Conventional - due to heating by the sun, warm air rises and condenses at higher altitudes then falls again.
Relief - warm air forced upwards by a barrier such as mountains, causing it to condense at higher altitudes and fall as rain.
Frontal - warm air rises over cool air when 2 bodies of air at different temperatures meet, because the warm air is less dense and lighter. It condenses at higher altitudes and falls as rain.
Water cycle outputs
Evapotranspiration - when water is heated by the sun (off plants) and becomes a gas.
Transpiration - occurs in plants when they respire (release h2O vapour through their leaves)
Streamflow - all water that enters a drainage basin will either leave through the atmosphere or through streams which drain the basin. These may flow as tributaries into other rivers or directly into lakes and oceans.
Water cycle flows - infiltration
Process of water moving from above ground into the soil.
Infiltration capacity - how quickly infiltration occurs.
Grass cops and tree roots create passage for water to flow through through from the surface into the soil, so increases the infiltration capacity.
Moderate / Fast
Water cycle flows - percolation
Water moves from the ground into porous rock or rock fractures. The percolation rate is dependant on the fractures that may be present in the rock and permability of the rock.
Slow
Water cycle flows - throughflow
Water moves through the soil and into streams or rivers. Speed of flow is dependant on the soil type.
Clay soils - high field capacity and smaller pore spaces have a slower rate.
Sandy soils - Darin quickly as lower field capacity and larger pore spaces and natural channels from animals such as worms.
Moderate / Fast
Water cycle flows - surface run off (overland flow)
Water flows above the ground as
- Sheet-Flow (lots of water flowing over a large area)
- Rills (small channels similar to steams, that are unlikely to carry water during periods where there is no rainfall)
Fast
Water cycle flows - Groundwater flow
Water moves through rocks - ensures theres water in rivers even in long periods of dry weather.
Jointed rocks (limestone) in karst environments where there are many underground streams and caves may transfer water very rapidly.
Usually slow but variable.
Water cycle flows - streamflow
Water the moves through established channels.
Fast
Water cycle flows - stem flow
Flows of water thats been intercepted by plants or trees, down a stem / leaf / branch or other part of a plant.
Fast
Water cycle stores and time lengths
Soil water - mid term (used by plants)
Groundwater - long term (porous rocks)
River channel - short term (water stored in river)
Interception - short term (water intercepted by plants)
Surface strange - variable (puddles, ponds, lakes)
Define the water table
Upper level at which the pore spaces and fractures in the ground become saturated.
Used by researchers to assess drought conditions, health of wetland systems and success of forest restoration.
Changes to water cycle LOCAL - deforestation
Less interception by trees so more surface run off.
Soil no longer held together by roots, soil water storage decreases.
Fewer plants to decrease in transpiration.
Changes to water cycle LOCAL - storm events
Large amounts of quick and high rainfall quickly saturate the ground to its field capacity. No more water can infiltrate for surface run off increases.
Strom events are less effective at recharging water stores than prolonged rainfall as over longer periods of time more water can percolate into ground water stores and there would be less overland flow.
Changes to water cycle LOCAL - seasonal changes
Spring - more vegetation growth so more interception
Summer - less rainfall, ground may be harder and more impermeable so increases surface flow.
Autumn - less vegetation so less interception and more rainfall (seasonal)
Winter - frozen ground may be imperials and encourage more runoff. Snow discourages runoff and takes time to melt, slowing down the process that occur in the water cycle.
Changes to water cycle LOCAL - agriculture
Pastoral farming - livestock trample the ground reducing infiltration.
Arable farming - ploughing increases infiltration by creating looser soil, Whcih decreases surface run off. However diffing drainage ditches increase run off and surface flow.
Hillside terracing - increases surface water storage and decreases surface run off.
Irrigation - can lead to ground water depletion
Changes to water cycle LOCAL - urbanisation
Creating roads and buildings which have impermeable surfaces are likely to have drains creates impermeable surfaces that reduce infiltration but increase the surface run off, reducing lag-time and increasing the flood risk.
Green roofs / SUDS - use grass to reduce the amount of impermeable surfaces helps tackle urban flooding
Define SUDS
Sustainable urban drainage systems
Soil water budget
Shows the annual balance between inputs and outputs in the water cycle and their impacts on the soil water storage availability.
Dependant on the depths the and permeability of the soil and bedrock. The maximum level of storage is called the field capacity.
Seasonal changes to the water cycles soil water budget
- autumn
Precipitation > evapotranspiration
Deciduous trees lose their leaves and the cooler temperatures mean that the plants photosynthesis less.
Soil moisture levels increase and a water surplus occurs.
Seasonal changes to the water cycles soil water budget
- winter
Potential evapotranspiration from plants reach a minimum due to the colder Tempe rates and precipitation continues to refill the soil and water stores.
Infiltration and percolation refill the water table.
Seasonal changes to the water cycles soil water budget
- spring
Feb-March = plants start to grow again and potential evapotranspiration increases as temperatures rise and plants photosynthesise more.
Water surplus still here.
Seasonal changes to the water cycles soil water budget
- summer
Hotter weather leads to utilisation of soil water as evapotranspiration rates peak and rainfall is minimal.
Evapotranspiration > precipitation
Soil water depletes and a water deficit may occur if there is long hot summer / spring or a lack of winter rainfall the year before.
Natural changes to the water cycle over time (and effects) - seasonal changes
Less precipitation, more evapotranspiration in summer because of higher temperatures.
Reduced flows in the water cycle in winter as water is stored as ice.
Reduced interception in winter, when deciduous trees lose their leaves.
Increased evapotranspiration in summer; deciduous trees have their leaves/higher temperatures.
Natural changes to the water cycle over time (and effects) - storm events
Causes sudden increases in rainfall, leading to flooding and replenishment of some water stores.
Unlikely to cause long term changes.
Natural changes to the water cycle over time (and effects) - droughts
Cause major stores to be depleted and the activity of flows acting within the water cycle to decrease.
May cause long-term change as they become more common as a result of climate change.
Natural changes to the water cycle over time (and effects) - El Niño and La Niña
The El Niño effect occurs every 2-7 years and causes warm temperatures in a predictable way.
The La Niña effect occurs every 2-7 years and causes cooler temperatures in a predictable way.
It is likely that climate change will increase the probability of more El Nino’s in future.
Natural changes to the water cycle over time (and effects) - cryospheric changes
In the past glaciers and icecaps have stored significant proportions of freshwater through the process of accumulation.
Currently, almost all of the world’s glaciers are shrinking, causing sea levels to rise.
If all the world’s glaciers and icecaps were to melt, sea levels would rise by around 60 metres.
Human changes to the water cycle over time (and effects) - farming practices
Ploughing breaks up the surface, increasing infiltration.
Arable farming (crops) can increase interception and evapotranspiration.
Pastoral (animal) farming compacts soil, reducing infiltration and increasing runoff.
Irrigation removes water from local rivers, decreasing their flow.
Human changes to the water cycle over time (and effects) - land use change
Deforestation (e.g. for farming) reduces interception, evapotranspiration and but infiltration increases (dead plant material in forests usually prevents infiltration).
Construction reduces infiltration and evapotranspiration, but increases runoff.
Human changes to the water cycle over time (and effects) - water abstraction
This reduces the volume of water in surface stores (e.g. lakes).
Water abstraction increases in dry seasons (e.g. water is needed for irrigation).
Human abstraction from aquifers as an output to meet water demands is often greater than inputs to the aquifer, leading to a decline in global long-term water stores.
Hydrosphere store
96.5% of all water on earth.
Includes process of ppt / runoff - these have minimal effect on the storage size however long term changes like increased water in sea etc. have a large effect.
Atmosphere store
0.001% water on earth.
Water removed and put into atmosphere by evaporation.
Plant transpiration.
Lithosphere store
1.7% of all water on earth
Longest term store.
Water cycle - local drainage basin inputs
Precipitation (rain/snow/hail)
3 types of precipitation - conventional / relief / frontal
Water cycle - local drainage basin outputs
Evapotranspiration
(Evaporation and transpiration)
Streamflow - all water that enters drainage basin will either leave through atmosphere or through streams which drain the basin. These may flow as tributaries into other rivers or into lakes and oceans.
Water cycle - local drainage basin flows
Infiltration
Percolation
Throughflow
Surface run off
Stream flow
Stem flow
Groundwater flow
Infiltration
Water moving from above ground into soil.
Grass crops and tree roots create passages for water to flow through from the surface (increase infiltration).
If precipitation > infiltration rate then more overland flow occurs.
MODERATE / FAST
Percolation
Water moving from the ground of roil Ito pourous rock or rock fractures.
Dependant on the number of fractures / porosity of the rock.
SLOW
Throughflow
Water moves through the soil and into streams or rivers.
Speed of flow is dependant on soil type. Clay soils - smaller pore spaces so slower rate, however sandy soils - lots of pore spaces so faster rate.
MODERATE/FAST
Surface run off
Sheetflow / Rills
FAST
Groundwater flow
Water that moves through rocks.
SLOW BUT VARIABLE
Streamflow
Water that moves through established channels.
FAST
Stem flow
Flow of water thats been intercepted by plants or trees , down a stem / leaf / branch / other part of plant.
FAST
Water cycle - local drainage basin stores (+length)
Soil water - mid-term
Ground water - long-term
River channel - short-term
Interception - short-term
Surface storage - variable
Water balance (eqn)
Equation used to express the process of water st orange and transfer in a drainage system.
Precipitation = (total runoff + evapotranspiration) +/- (change in) store.
The water cycle - global scale
Global water cycle is compromised of many stores, the largest being oceans which contain 97% global water.
Only 2.5% of stores are freshwater and 70% of this is stores in the cryosphere and the other 30% lithosphere as groundwater. 1% of this is made up of surface freshwater stores.
Gives the 5 main stores
Hydrosphere - liquid water
Lithosphere - ground water
Biosphere - living organisms
Cryosphere - frozen
Atmosphere - water vapour
Aquifers (storage time and distribution)
Underground water stores and on a global scale they’re unevenly distributed.
Shallow aquifers can store water for up to 200 years but deeper aquifers up to 10,000years.
Global atmospheric circulation model + cells
Main factor that determines cloud formation and rainfall.
- There are different zones of rising and falling air that leads to precipitation through conventional rainfall.
- This creates a low pressure zone on the equator (ITCZ), and has very heavy rainfall.
- This zone moves during seasons (N+S).
Where the Ferrel and Hadley cells meet, unstable weather conditions occur and moved by jet-stream, this causes the UK to have changeable weather.
Flood hydrographs
Used to represent rainfall for the drainage basin of a river and the discharge of the same river on the graph.
Flood hydrographs - discharge
Volume of water passing through a cross sectional point of the river at any one point in time.
Made of base flow and strom flow.
Flood hydrographs - rising limb
Line on the graph representing discharge increasing
Flood hydrographs - falling limb
Line on the graph that represents the discharge decreasing
Flood hydrographs - lag time
Time between peak rainfall and peak discharge
Flood hydrographs - base flow
Level of groundwater flow
Flood hydrographs - storm flow
Compromised of overland flow and through flow
Flood hydrographs - bankfull discharge
Maximum capacity of the river. If discharge exceeds this then the river will burst its banks - flooding.
Flashy hydrograph vs subdued hydrograph
Flashy - short lang time and high peak discharge. More likely to occur during a storm event, with favourable drainage basin characteristics.
Subdued - long lag time and low peak discharge.
Features of flashy hydrograph
Short lag time
Steep rising limb and falling limb
Higher flood risk
High peak discharge
Features of subdued hydrograph
Long lag time
Gradually rising falling limb
Lower flood risk
Low peak discharge
Natural features that increase surface run off / decrease lag time
High rainfall intensity
Antecedent rainfall
Impermeable underlying geology
High drainage density
Small basin
Circular basin
Low temperatures
Precipitation type
Vegetation cover
Effect on natural lag time - high rainfall intensity
Higher discharge potential from the river so more likely for soil to reach its field capacity, thus increasing surface run off and decreasing lag time.
Effect on natural lag time - antecedent rainfall
Rainfall that occurs before the studied rainfall energy (ground more saturated).
Increased surface run off as ground is saturated and soils field capacity has been reached.
Effect on natural lag time - impermeable underlying rock
Decreased percolation and therefore greater levels of through flow
Effect on natural lag time - high drainage density
Many tributaries to main river increasing speed of drainage and decreasing lag time
Effect on natural lag time - small basin
Rainfall reaches the central river more rapidly - decreased lag time
Effect on natural lag time - low temperatures
Less evapotranspiration so greater peak discharge
Effect on natural lag time - precipitation type
Snow or hail takes time to melt before moving toward the river so rainfall increases the flood risk.
Effect on natural lag time - vegetation cover
Forested areas intercept rainfall, decreasing flood risk but exported areas will transfer water to the river more rapidly, decreasing lag time.
Human features that increase surface run off / decrease lag time
Urbanisation
Pastoral farming
Deforestation
Effect on human lag time - urbanisation
More impermeable surfaces, so increased runoff and surface storage and infiltration are reduced.
Effect on human lag time - pastoral faming
Ground trampled so less interception and more surface runoff.
Effect on human lag time - deforestation
Less interception by trees so water reached ground and rover more quickly.
More surface run off - greater flood risk.
Case Study - River Brock
Location – Lancashire
Size pf catchment area – 40 km2
Length of the River Brock – 17.8 km
Source of the River Brock – west facing slopes
Mouth of the River Brock – joins The Wyre which drains to the Irish Sea.
Case Study - River Brock (upper course)
More rural, more permeable surfaces - less succeptible to flooding than the middle course which is urbanised.
More steep relief - more run off (500m)
Around the source - soil type is peat and rock type is milestone grit - impermeable.
Moorland vegetation - interception store will be low but peat is permeable (and easily saturated)
Case Study - River Brock (Myerscough Agricultural College)
- Has a licence that allows them to abstract a maximum of 45.46m3 daily.
- This decreases water discharge however it’s unlikely to lead to water over-abstraction because it’s carefully monitored by the Environment Agency. Water abstraction reduces the natural flow of the river, which reduces habitat for fish and river discharge.
Case Study - River Brock (October 1980)
Flooding is not an issue until the river approaches the confluence with the River Wyre. Here the gradient of the land is much less.
October 1980 – St Michaels on Wyre – combination of intense and prolonged rainfall that means 400 houses were affected.
Case Study - River Brock - What protection programs were put in place after 1980 flooding?
- EA constructed a flood storage basin for a one in fifty-year flood. Has the capacity to store 1.7 million cubic meters of floodwater.
- Embankments raised to 3m.
- Meanders of the River Brock were cut off so that water left the area quickly.
- The most vulnerable flood plain has been left free of buildings.
Middle / Lower course of the River Brock
More urbanised - built environment is more impermeabe so more overland flow
- also may have SUDS - sustainable urban drainage systems) (eg. M6 / Bilsborough)
Less steep relief - less run off
Sherwood sandstone at the channel / mouth which is 97% permeable and overlay by boulder clay.
More influence by human characteristics + Likelihood of flooding is greater.
Myerscough Agricultural College extract a maximum of 45.46m3 of water from the River Brock every day.
