Hydrology Flashcards
Why is water our most precious resource
supports all life on earth, limited supply
what un sustainanle development goal is water linked to
sdg 6 clean water and sanitation
what are sdg6 key goals
safe drinking water, adequate sanitation, good water quality, sustainable water use, resource management and protect ecosystems
What type of bonding does water form
hydrogen bonding and is extremely polar
Why is water a universal solvent
capable of dissolving more substances than any other liquid, only if H bonds can be overcome- if not precipitate forms
Hydrophillic
can dissolve in water
Hydrophobic
cannot dissolve in water
Density of water
only common liquid that expands when frozen, ice is 90% of that of water
What is the specific heat capacity (of water)
the energy required for a particular change in temperature 4.186 J g-1 c-1
-> high so water respinds to changes in air temp slowly
What is the specific latent heat
the energy required for a particular change in state
333.4 Jg-1 to melt ice without changing its temperature
2462 Jg-1 to evaporate water without changing its temperature
What is surface tension
the surface of a liquid to resist external force
Property of waters surface tension
due to fewer molecules at waters surface they cling to each other stronger making a strong barrier between water and the atmosphere
What is a rivers cathcment
the area around a river where precipitation will flow to that river, used to study the hydrological cycle of a river
What is the boundary between two cathchments known as
watershed
What makes up a hydrological cylce
inputs, stores and outputs
What is the equation to measure catchment water balance
P=Q+ET+L+⯅S
P= catchment precipitation
Q= catchment runoff
ET= catchment evapotranspiration
L= catchment leakage
⯅S= change in catchment storage
over time inputs must balance outputs plus increase in storgae
Application of water balances
decisions to manage water resources in a catchment
eg HEP, irrigation, resourvoirs, risk assessments for flooding etc
What is an event hydrograph
how catchment responds to a specific event eg storm
what is an annual hydrograph
plots the traditional water year, oct-sep
Why is the water year oct-sep
to account for spring melt, so all water measured actually fell within water year
What is a flashy hydrograph
one with lots of peaks due to responses to lots of extreme weather events
What is the lag time
the time between peak rainfall and peak river discharge- can be controlled by elements of catchment
eg urban with no infiltration have short lag time
Elements of a hydrogrpah
discharge -> base flow, rising and falling limb, peak discharge
rainfall- peak rainfall
What are the three categories of weather
precipitation
obscurations(any phenomena in atmosphere that reduces visibility vertically)
other phenomena(wind related)
What is precipitation
any form of water particle, whether liquid or solid, that falls from the atmosphere and reaches the ground
Characterisation of rain
drops larger that 0.5 mm, or if smaller are separated
Characterisation of drizzle
uniform precipitation made of fine drops close together, appears to ‘float’
Characterisation of snow
branched and in the form of six-pointed stars.
Characteristion of snow grains
very small, white, and opaque grains of ice. Basically, this is frozen drizzle
Characterisation of ice crystals
falling crystals of ice in the form of needles, columns, or plates. Also called ‘diamond dust’, ice crystals appear like fog with individual water particles forming directly as ice
Characterisation of ice pellets(sleet)
transparent or translucent pellets of ice, which are round or irregular hard grains of ice consisting of frozen raindrops, or largely melted then refrozen snowflake
Characterisation of hail
small balls or other pieces of ice falling separately or frozen together in irregular lumps. Associated with thunderstorms, individual hail stones are ¼ inch (5 mm) or greater in diameter
What are forms of condensation
fog, mist, dew, clouds
What is condensation
the process where water vapor becomes liquid
What are the ways condensation happens
air becomes so saturated with vapor that it cannot hold anymore
air is cooled to its dew point
What is dew point
the temperature at which condensation happens
What is relative humidity
The relationship of how much water a given mass of air actually holds compared to the amount it can hold
What affects airs ability to hold water
temperature eg 20c water can hold 2x as much than at 10c
hot air expands and rises
cold air contracts and sinks
When is air said to be saturated
When air holds as much water vapor as it can for a given temperature (100% relative humidity)
Nimbostratus characteristics
continual precip that lasts for hours, low lying and full of moisture
What are the two clouds that bring precipitation
nimbostratus and cumulonimbus
What are condensation nuclei
they provide a surface for water to condense on
very small particles eg dust, pollen, salt spray
Cumulonimbus characteristics
produce rain thunder and lightning, occur at cold fronts
How is precipitation formed
particles are uplifted, dew point is low so ice crystals form, crystals combine to make larger flakes, process continues until flake is so heavy it falls and melts to form raindrops
What is cyclonic uplift
Cyclonic precipitation is caused by the lifting of an air mass because of the pressure difference
If low pressure occurs at an area, air will flow horizontally from the surrounding area, causing the air at the low-pressure area to lift
What are the two types of cyclonic precipitation
frontal- differences between warm and cold fronts
non frontal- warm air is stationary and cold air meets it
What are the characteristics of a cold front
cold air mass drives out a warm air mass
Intense precipitation in comparatively small area
What are the characteristics of a warm front
warm air mass replaces the retreating cold air mass
Less intense precipitation but is spread over a comparatively larger area
What is convective uplift
occurs in equatorial areas
surface is heated by the sun, air rises and cools then reaches its saturation limit to form precipitation
results in intense short lived rainfall events
What is orographic uplift
moist air mass meets physical barriers causing air to rise up, condense and precipitate
rain concentrated on windward side of barrier-> leads to rain shadow
What areas of the planet receive the most precipitation
those with convergent air masses
eg at equator, 60*
Characteristics of cyclonic rainfall
covers extensive areas but with local intense cells
lead to regional flooding and highest daily falls in uk
Characteristics of convective rainfall
very intense but localised and short lived
can generate flash floods
What are the three temporal patterns of measuring rainfall
long term- average conditions
medium term- seasonal, irrigation schedules
short term- forcasting
What is evapotranspiration
the sum of all processes by which water moves from the land surface to the atmosphere via evaporation and transpiration
What is evaporation
Vaporisation of liquid water into water vapour. Water moves from the Earth’s surface to the atmosphere
What is transpiration
Evaporation of water from plants occurring at the leaves
What are the three requirements for evaporation to occur
water available at surface
unsaturated air
energy supply
What are the two main types of energy supply for evaporation
net radiation- energy available due to the balance of incoming and outgoing radiation
sensible heat- energy transferred from a warmer body to a cooler one, e.g. transfer of energy from air to cooler water on ground surface
When does transpiration occur
when the plant leaves its stomata open for photosynthesis
What is potential evapotranspiration (PE)
The maximum amount of water that would be evapotranspired if enough water were available (from precipitation and soil moisture).
What is actual evapotranspiration (ET)
The actual amount of water which is evapotranspired and is limited by the amount of water that is available
ET will always be less than or equal to PE
How to measure evaporation
lysimeters
What is a lysimeter
water tight tank containing soil and plants growing in the same field
Evapotranspiration is estimated in terms of the amount of water required to maintain constant moisture conditions within the tan
What are the two methods for estimating evapotranspiration
thornthwaite
penman monteith
What are the factors that effect evapotranspiration
temperature- air is warmer rates go up, warm cause stomata to open
water availability
energy availability
humidity gradient
wind speed
physical attributes of vegetation- height, leaf area
stomata resistance
soil characteristics- clay hold water
What is the water table
The boundary between the unsaturated zone and the saturated zone underground
What is groundwater
The water found underground in the cracks and spaces in soil, sand and rock. It is stored in and moves slowly through geologic formations of soil, sand and rocks called aquifers
What is an aquifer
A body of rock and/or sediment that holds groundwater
What is infiltration
The flow of water from aboveground into the subsurface
What is percolation
The downward movement of water through the soil
What is capillary rise
upward movement of water during periods of moisture deficit (dry periods)
What is infiltration capacity
The maximum rate at which a soil in any given condition is capable of absorbing water.
What does the infiltration capacity regulate
determining whether streamflow is derived from the surface (overland flow) or the sub-surface (throughflow)
What is the infiltration rate
The rate at which the water actually infiltrates through the soil during a storm
What happens when rainfall intensity is greater than the infiltration capacity
rainfall excess occurs and infiltration excess overland flow occurs
What happens to the infiltration capacity as the moisture content of soil increases
decreases
What factors effect infiltration rates
storm characteristics
land surface condition
soil characteristics
vegetation cover
surface soil and water temperature
What is hydraulic conductivity(K)
term used to describe how easily fluid moves through a porous medium
What is saturated fluid conductivity(Ksat)
when all pores are full of water
When does groundwater move vertically
the unsaturated zone
When does groundwater move horizontally
the saturated zone
What is the capillary fringe
a zone in the soil just above the water table that remains saturated or almost saturated, because the water is drawn up against the force of gravity due to waters adhesive and cohesive forces (capillary action)
Aquifer characteristics- porosity
fractional volume occupied by pores(hold) ie spaces between particles
Aquifer characteristics- permeability
capacity for water throughput(yield) ie can water pass through pores
What is a confined aquifer
surrounded by nonpermeable substance
What is an unconfined aquifer
not surrounded so water can leave
What is a perched aquifer
local importance only
impermeable rock above water table that water sits above
What is direct(percolation) groundwater recharge
rainfall or snowmelt leads to widespread infiltration of soil and then vertically down to groundwater
What is indirect groundwater recharge
input translated first to overland flow or streamflow, but reaches groundwater in areas of locally high permeability
What is hydraulic head
water flowing from areas of high to low gravitational potential
What is managed groundwater recharge
in times of surplus the aquifer is artificially recharged and used in times of shortage
Define a flood
an overflow of a large amount of water beyond its normal limits, especially over what is normally dry land
What is a river(fluvial) flood
flood from river to a flood plain
what is a flash flood
intense rainfall over a short period of time
what is surface(pluvial) flooding
urban areas with overwhelmed drainage
what is a coastal(tidal) flood
changes in climate cause sea levels to change and storm conditions to arise
What is groundwater flooding
infrastructure built low down and water rises
What causes flooding
precipitation intensity, duration, and extent
what is the return period of a flood
average interval between exceedence of some threshold eg 1 in 200 year flood
what is the annual probability of a flood
estimated probability of a flood happening in a given year
what is a frontal system in a flood
prolonged, low-moderate intensity, dangerous when stationary
What is convective rainfall in a flood
localised, short duration, high, intensity, enhanced over hills and urban areas, summer seasonality
What are factors that intensify flooding
frozen, compacted or parched ground
degree of saturation
impermeable surfaces
land management changes
What is a meteorological drought
extended period of dry weather
What is a hydrological drought
water supply starts to fall below normal
What is an agricultural drought
water shortage damages cropss
what is an ecological drought
widespread ecological damage due to lack of water
what is a socioeconomic drought
water supply affects supply/demand commodities
What is the standardised precipitation index
a drought indice used to characterise a drought in the uk
What factors affect the severity of a drought
duration
accumulated deficit
mean deficit
maximum intensity
What does the term water quality refer to?
the biological, physical and chemical properties of water
What does biological water quality measure
diversity and abundance within a given stretch of river of fish, invertebrates , macrophytes and algae
What does morphological water quality measure?
the physical structure of the river and issues of river continuity for river straightening, culverting, impounding and substrate manipulation
What does phsiochemical water quality measure?
measuring concentration or level at a specific point on the river
eg pH nutrients oxygen tmep sediment emerging pollutants
What is point pollution
Where the source directly enters the water body at a specific point
What is diffuse pollution
Where the source enters the water body through the landscape
What is eutrophication
The enrichment of water by nutrients, especially compounds of nitrogen and/or phosphorus, causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of the water concerned
