Water balance and changes - P Flashcards
what is a drainage basin
an area of land drained by a river and its tributaries
what is a catchment
the area of a drainage basin e.g. the amazons is 7 million km squared
what creates dynamic equilibrium
water continually entering and leaving a drainage basin
what is a river system
a river and its tributaries make up a river system also called a drainage basin/watershed
what is a watershed
includes the river, all its tributaries and any groundwater resources in the area
what is the river mouth
the end of a river - where it empties into another body of water like the ocean, lake etc.
what is the water balance
the balance between inputs and outputs in a drainage basin - usually shown on a graph
what is the equation for the water balance
P = Q + E +/- changes in storage
P - precipitation
Q - runoff
E - evapotranspiration
what does a watershed mark
the boundary between two separate drainage basins
are drainage basins open or closed systems
open systems - receive inputs and outputs
what happens to water in a drainage basin after precipitation
water will flow downstream from the source, tributaries will join together creating a confluence before flowing out to sea at the mouth
what are the 10 types of flowing
channel flow
surface runoff
infiltration
throughflow
percolation
interflow
groundwater flow
baseflow
throughfall
stemflow
what is interflow
when water travels through permeable rock above the water table
what is baseflow
when water feeds onto the channel through the banks and bed
how is water stored in the cycle; through interception
vegetation storage
surface storage
groundwater storage
channel storage
what are the outputs of water
evapotranspiration
evaporation
transpiration
runoff into the sea
what are the three factors that could affect the water balance (there are more than 3 but we only needed 3 examples)
temperature
human activity
rainfall
how could temperature affect the water balance
increases evaporation and transpiration in higher temperature.
decreases evaporation and transpiration in lower temperatures
how does human activity affect the water balance
may release fossil fuels so there are more nuclei for clouds to from around so increased precipitation
how could rainfall affect the water balance
more rainfall causes more inputs of water (precipitation)
less rainfall causes less inputs of water (precipitation)
what is a catchment
the area of land within a drainage basin which includes everything within it
what is river discharge
the volume of water passing a given point at a given time. Measured in cumecs (m**3/s)
what is the equation of discharge
discharge = cross sectional area x velocity
why is it important to monitor river discharge
can anticipate floods & shortages
detecting climatic and environmental change
allows the assessment and management of water resources, the design for water-related structures and flood warning schemes.
what is a method of measuring river discharge
the float method
describe the steps of the float method
- mark two points along the channel (this is the distance)
- measure 3 depths and find the average (depth)
- measure the rivers width (width)
- fill a float bottle partially with water
- drop bottle and start the timer stop the timer when it reaches the second observer.
- repeat step 5 3 times and find the average (time)
- determine flow:
width x depth x (distance / time) x correction factor
what is a water budget
the annual balance between precipitation, runoff and evapotranspiration (inputs and outputs)
what is the equation for the water budget
P = Q + E
P - precipitation
Q - runoff
E - evapotranspiration
what does a positive water budget mean
water surplus (inputs > outputs)
what does a negative water budget mean
water deficit (inputs < outputs)
what do water budgets at a national/regional scale show
the amount available for human use
what do water budgets at a local scale show us
the available soil water
what happens to a water budget in the winter
precipitation exceeds evaporation - soil moisture is recharged until a surplus - water can then supply rivers
what happens to a water budget in the summer
evaporation exceeds precipitation - soil water is utilised - by the second half of summer there is a deficit
what happens to the water budget in autumn
precipitation increases and evapotranspiration falls allowing soil moisture to be recharged once more
what are the main human impacts on the global water cycle
deforestation
water abstraction
agriculture
what happens to the percentage of surface runoff when human settlements are created
goes from less than 1% to 20-30% - increase
what happens to the percentage of evapotranspiration when human settlements are created
goes from 40-50% to 20-30% - decrease
what happens to the percentage of interflow when human settlements are created
goes from 20-30% to 0-30% - decrease
what happens to the percentage of groundwater when human settlements are created
goes from 10-40% to 10-20% - decrease
Where is the river kennet
in southern England in Wiltshire and Berkshire
how large is the river kennet catchment
1200 km**2
what material is the upper catchment of the river kennet
chalk which is highly permeable so groundwater is the largest flow
when the water from the river kennet is filtered through chalk what happens to it
it will have high oxygen levels and is fast flowing with exceptional clarity
what are the native fauna in the river kennet catchment
white clawed crayfish, otters, water voles
what is the largest Urban area relying on a water supply from the river kennet
Swindon with a population of 220,000
what does the river kennet supply water for
local industries: agriculture, public use
which river abstracts water from the upper catchment with boreholes
The river Thames - none of the water is returned
what are the impacts of water extraction on the river kennet
- rates of extraction exceed rates of recharge reducing flows by 10-14%
- during the 2003 drought flows fell by 20% in the 1990 with dry conditions they fell by 40%
- lower flows have reduced flooding
- springs have dried up and reduced saturated overland flow
Where is California located
California is a state on the far west of North America
what foes California have that is used in periods of drought
has crucial water reserves used in droughts
since which year has California been regulating surface water
since 1914
when did California start regulating groundwater
2014 (100 years after the regulation of surface water)
what percentage of the population rely on groundwater supplies in California
85% of the population and $50 billion of the agriculture industry
how many people rely solely on groundwater
6 million
how much of the water supply do groundwater stores usually supply in California
30-40% however in drought this has almost doubled
Which valley is using pumps and causing the groundwater stores to drain
Central Valley where they are are withdrawing twice as much as nature is replenishing.
what does groundwater extraction cause
ground subsidence
what is ground subsidence
when water is removed from the groundwater basin clay layers are drained causing clay layers to compact which cause compaction in aquifers.
what does the compaction in ground subsidence cause
compaction leads to fewer pore spaces so recharging is harder
what act was adopted in California 2014
Sustainable Groundwater management act (SGMA) - groundwater is managed sustainably - if plans are inadequate the state authority can step in
what are the solutions to more water being taken out than can be replenished
control groundwater withdrawals
deposit water into water storage either naturally or artificially:
- naturally by recharge
- artificially by creating a recharging pond so water will infiltrate
