Hydrology

Front 1

Hydrology

Back 1

the study of water

Front 2

Catchment (River Basin)

Back 2

The area of land from which water flows towards a river and then in that river to the sea

Front 3

Hydrologic Cycle

Back 3

A conceptual model of how water moves around between the earth and atm

Front 4

Water Balance Equation

Back 4

A mathematical description of the hydrological processes operating within a given time frame and incorperates principles of mass NRG continuity
inputs = outputs
0 = P +/- E +/- change S +/- Q
P=Precip, E = evap, S = change in storage, Q = Runoff
P = R+E+G

Front 5

What are 3 computer modelling strategies?

Back 5

1. Black Box Models
- simplest one
- puts different hydrological processes that we know influence way water moves into single regression relationship
- widely applicable but restricts its usefulness
2. Lumped Conceptual Models
- formulating the hydrological cycle into a water budget model that allows simulation of streamflow while also being able to see the individual processes operating
3. Physically based distributed models
- all processes within a catchment are simulated as a series of physical equations at points distributed throughout the catchment
- no calibration required
- numerous problems

Front 6

Why are theoretical or simplified equations rarely used in the "real world"?

Back 6

Real world applications require either:
(1) empirical equations (need constant calibration)
OR
(2) very complicated and complex physically based equations

Front 7

Reservoir

Back 7

storage, oceans not part of hydrologic cycle so most water on earth not in cycle and atm has tiny amount of water (v. short term storage), most glaciers and ice caps and ground water

Front 8

Annual Flux

Back 8

Exap and Precip are equal over a year most evap from oceans in BC most water evap comes from Pacific. We have valley cloud from the lake evap but does not really create enough precip not like the great lakes. for precip we are more interested in terrestrial not oceanic

Front 9

Darcy Law

Back 9

Way a liquid flows through a porus medium

Front 10

Neutonian Fluid

Back 10

deformation to exact proportion of stress applied

Front 11

Quantity of Water

Back 11

Three times more abundant than all other substances combined, 6 times more abundant than the next most abundant substance (feldspar), water is a part of almost every process

Front 12

State of Aggregation of Water

Back 12

- Almost the only inorganic liquid in nature
- only substance to occur naturally in all 3 phases
- reason it is able to do this is because of hydrogen bonds

Front 13

Solvent Power of Water

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- more general and greater than any other liquid
- charged ends of water mcl attracted to other charged substances, material stays in solution
- water can hold many times its own weight in ions
- means there is no practice upper limit on how much dissolved material rivers can carry, will depend on rate of chemical weathering
- can also hold lots of pollutants and dissolved substances, especially in ground water

Front 14

Surface Tension and Capillarity

Back 14

- highest of all liquids except mercury
- surface tension (cohesion), wetting (adhesion)
- high surface tension means, lots of NRG to change phase, lots of NRG to biol or freeze, would have no soil moisture short time after rainstorm, no plant life, holds together soil particles, like glue (with lots of substances)

Front 15

Expansion on Freezing

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- Exceptionally great (9%), shared by a few other substances
- goes fro 999-1000kg/m3 when liquid, to 890-900 when frozen
- Because of this ice forms on the surfae of water
- Freeze Thaw weathering

Front 16

Expansion on Heating

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- Great, smallest volume (i.e max density) at +4 degrees
- this is because the hydrogen bonds are so strong that they do not allow the water to shrink any further
- as water warms up it becomes less dense and becomes harder to mix (warm on surface, cooler below), once cools down get lake turnover
- Implications:
--O2 rich bottom mix
-- warm surface water evaporate more readily
-- dams and reserviors let out the cold water from the hypo when releasing water leaving behind warmer water and increased evaporation

Front 17

Thermal Capacity of Water

Back 17

- Greatest of all liquids except ammonia
- Specific heat of water is 5x greater than that of air or soil
- large bodies of water effect climate because they can store heat

Front 18

Specific Heat Capacity

Back 18

Amount of NRG required to raise the temperature of a unit mass of a substance by 1 degree Celsius

Front 19

Latent Heat

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- of water very high
- the NRG required to change water from one phase to another (needed to break the H-bonds)
- In the phase changes of water NRG is either released (heathing; latent heat --> sensible heat_ OR absorbed (cooling; sensible heat --> latent heat)

Front 20

Sensible Heat

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the heat which can be sensed or felt, most easily understood as the heat we fell as warmth, the sensible heat flux is the rate of flow of that sensible heat

Front 21

Thermal Conductivity of Water

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- Greatest of all liquids except mercury
- Water conducts heat in 2 ways:
(1) Conduction: mcl to mcl transfer of heat (can occur in liquid and in solid)
(2) Convection: water moving and taking NRG with it

Front 22

Electrical Conductivity of Water

Back 22

Pure water has v. low electrical conductivity (is an excellent indicator) but dissolved ions increase conductivity dramatically

Front 23

Transparency

Back 23

- to electromagnetic radiation
- Albedo, ability of substance to reflect light, dry snow stays cold because it reflects so much light that it cant melt

Front 24

Compressibility of Water

Back 24

almost none due to the strength of hydrogen bonds

Front 25

Mobility

Back 25

- Great in all three states
- snowpack creep, glacial flow

Front 26

Are these "cooling" or "heating"
(1) Sublimation
(2) Freezing
(3) Evaporation
(4) Deposition
(5) Melting
(6) Condensation

Back 26

(1) Cooling (Solid to Gas): Sensible to Latent
(2) Heating (Liquid to Solid): Latent to Sensible
(3) Cooling (Liquid to Solid): Sensible to Latent
(4) Heating (Gas to Solid): Latent to Sensible
(5) Cooling (Solid to Liquid): Sensible to Latent
(6) Heating (Gas to Solid): Latent to Sensible

Front 27

Fog Drip

Back 27

Tiny water droplets suspended in fog which are "harvested" by an object (ex. vegetation) protruding into the fog
- accumulate up to 4mm/hr

Front 28

Rime (ice)

Back 28

tiny super cooled droplets suspended in fog which are "harvested" by a sub-freezing object protruding into the fog, the droplets freeze as soon as they strike the sub-freezing object

Front 29

Dew

Back 29

Water vapour which condenses onto any surface once a thin layer of the atm adjacent to the surface drops below the dewpoint temp
- 0.1-1mm/night
- Study in Ohio could be approx 12mm per month due to humidity

Front 30

Hoar Frost

Back 30

Water vapour which sublimates onto any surface once a thin layer of the atm adjacent to the surface drops below 0 degrees as well as below the dew point temp

Front 31

Drizzle

Back 31

Water droplets <0.5mm in diameter falling when surface temps are well above 0 degrees
- 0.2-0.5 mm/hr

Front 32

Rain

Back 32

Water droplets >0.5mm in diameter falling when surface temps are well above 0 degrees
- Light: <2mm/hr
- Heavy: >7mm/hr

Front 33

Snowflakes

Back 33

Aggregations of ice crystals up to several cm across, reaching the ground at air temp as high as a few degrees above freezing

Front 34

Graupel

Back 34

Opaque pellets of ice 2-7mm in diameter falling in showers, produced by riming of ice crystals, also knows as soft hail or snow pellets
- when the stellar gets completely covered with frost, white fluffy opaque, turbulant

Front 35

Sleet

Back 35

British term for partly melted snow or a rain-and-snow mixture, usually falls when surface temperatures are a few degrees above 0 degrees

Front 36

Freezing Rain/ Freezing Drizzle

Back 36

Super cooled drizzle or rain which freezes immediately upon landing on a sub-freezing surface (ex. car, road, windsheild)

Front 37

Ice Pellets

Back 37

Frozen rain or drizzle drops, sometimes with clear ice encasing a snowflake or graupel, also known as "sleet" in the US

Front 38

Hail

Back 38

Roughly spherical lumps of ice 5-50mm or more in diameter, exhibiting in cross section a layered structure of alternating bands of opaque and clear ice
- associated with summer thunderstorms, nothing to do with winter

Front 39

Why are hydrologists interested in precipitation?

Back 39

-largest flux in hydrologic cycle
- only input in terrestrial cycle

Front 40

How does dew form?

Back 40

Layer of cold air forms next to the ground, calm conditions so no clouds. fog in sky, warm air rises, cold layer next to ground reaches relative humidity of 100% and dew forms

Front 41

Dry Adiabatic Lapse Rate

Back 41

rate at which air cools when you lift it (average is 10 degrees per 1000m)

Front 42

Adiabatic Process

Back 42

Process that occurs without the transfer of heat or matter between a system and its surroundings
- Heating:occurs when the pressure of a gas is increased from work done on it by its surroundings
- Cooling: occurs when the pressure of a substance is decreased as it does work on its surroundings
--occurs in the Earth's atmosphere with orographic lifting and lee waves, and this can form pileus or lenticular clouds if the air is cooled below the dew point

Front 43

Saturated Adiabatic Lapse Rate

Back 43

- <10 degrees per 1000m
rate of cooling always less than dry because it has to release some water vapour out of it as it cools, releasing latent heat into sensible heat in the process of condensation, the degree it is lower by depends on how much condensation is actually going on

Front 44

What are 3 mechanisms by which we lift air?

Back 44

- most effective way to cool air is by lifting it
(1) Convective Lifting: heat air, it expands/becomes bouyant, rises
-- summer heating over land (thunderstorms)
-- cold moist air moving over a warmer sea.land surface
--individual, violent convection cells in a tropical cyclone
-- localized and complicated spatial pattern
(2) Frontal Lifting: inside mid-latitude cyclones
-- intensity of rain lower but storm total are greater, more consistent over a long period of time
(3) Orographic Lifting:air masses moving over mountains or small oceanic islands, not much lifting required

Front 45

What are 3 precipitation mechanisms?

Back 45

(1) Droplet Coalescence
large drops fall faster then small drops due to their larger mass to surface area ration, large drops catch up to small drops and suck them in due to polarity
(2) Bergeron-Findeisen Mechanism
(3) Riming
- Super cooled water droplet instantly freezes onto a cold surface

Front 46

Classifying New Snow

Back 46

EX. F2rwD3.0
- F2 = Stellar Crystal
- r = rimmed
- w = wet
- D3.0 = diameter (refers to individual crystals not the ones that stick together)

Front 47

C-axis Growth vs A-axis Growth

Back 47

- Columned vertical growth (c-axis)
- Horizontal growth (a-axis)

Front 48

What are 5 issues related to measuring precipitation

Back 48

(1) Differences between gauges and techniques
- different types of instruments and different ways of measurements
(2) Wind-Generated undercatch
- less precip measured then actually falling when have wind, snowfall will be underestimated severely
(3) Evaporation, especially from storage gauges
(4) "bridging" by snowfall
- Get cap of snow over top of gauge, mushroom like, then no more snow into gauge
(5) Point measurements of an areal phenomenon
- not uniform over whole basin

Front 49

What two things does the accuracy of precipitation gauge network depend on?

Back 49

(1) Spatial variability of precip, which is greatest with:
(a) rugged topography
(b) lifting mechanisms (convection cells have the greatest effect) convection precip
(2) Time scale of interest
- shorter time scale = more variability (averaged over longer period makes more uniform)

Front 50

What are two ways that we can increase the accuracy of precipitation measurements?

Back 50

(1) have more gauges, not always possible
(2) Put in better places (lots in airports and farms because there is someone there everyday to take the measurements), want to put in a place that represents the basin

Front 51

What are 2 technologies that assist in taking precipitation measurements, and what are their problems?

Back 51

(1) Groundbased Radar
- sending out radar beam that gets reflected by precip (better by rain then snow), radar returns and paints a pic of precip
- not particularly accurate, good idea of where it is falling
- has to be ground based not satellite, will reflect off ground over whelming snow and rain fall return
(2) Infra-red Satellite Imagery
- Measures the temp of clouds
- spatial veiw of where it is occuring
- colder temps = higher clouds = more precip held
- doesnt allow to measure amount

Front 52

List and describe 3 temporal variations in precipitation (change over time)

Back 52

(1) Stoichastic (random): produced by random variations in timing and magnitude of storms
- dry climate - all precip for the year can be caused by a few storms
(2)Periodic Variations: Diunral scale (24hrs), seasonal (monsoon), quazi-regular multi year variations (cyclide, ElNino Southern Ossilation, NAO)
(3) Secular/Historic (centuries-millenia): milankovitch cycle, Chandler Wobble

Front 53

What 5 factors control snow cover distribution?

Back 53

(1) Temperature
(2) Wind
(3) NRG and Moisture transfer
(4) Physiography (elevation, slope, aspect, roughness, optical and thermal properties of materials underlying the snowcover)
5. vegetation cover

Front 54

List the terrains from largest to smallest distance that snow will travel over

Back 54

Polar ice Caps (up to 30-50km)
Ice Domes (up to 5km)
Plateaus of Southeast Wyoming (larger particles (1.4km), smaller particles (0.5km)
Plains of western siberia (1-3km)
Mountainous, dissected topography (0.1-0.5km)

Front 55

Snow Distribution

Back 55

(1) Areal Extent (km2 or percentage of basin covered by snow)
(2) Snow Cover Water Equivalence (SWE)
- SWE (cm) = (snow depth (cm)) x (snow denisty (kg/m3)/water density (kg/m3))

Front 56

What are the 4 types of snow metamorphism?

Back 56

(1) Equilibrium Metamorphism
(2) Kinetic Metamorphism
(3) Melt-Freeze Metamorphism
(4) Pressure Metamorphism

Front 57

Equilibrium Metamorphism

Back 57

"equi-temperature" or "destructive metamorphism"
- occurs when steep temperature gradient in the snow pack or layer is absent, transfer of water vapour in the snowpack or layer is in this case limited to individual snow grains
- In this process the individual grains get rounded and strong necks for between adjacent grains through a process called sintering
- Rounding occurs because the shape of the original snow grains this thermodynamically unstable, the rounding minimises the surface area to volume ratio of the grains, the end result is a settling of the snowpack over a period of hours to weeks, the rate of settling being dependant on the absolute temperature, the snowpack or layer is also significantly strengthened by the formation of the necks between grains, snow grains in advanced stages of equilibrium metamorphism are called rounds or monocrystals

Front 58

Kinetic Metamorphism

Back 58

- also refered to as "kinetic growth" and "temperature gradient" or "constructive metamorphism"
- occurs when the snowpacks or layers temperature gradient is sufficiently steep (typically>/= to 10 degrees/m) to also produce a significant vapour pressure gradient, vapour transfer occurs upward through the snowpack or layer
- Deposition of the upward movement of water vapour occurs on grains instead of at grain contacts, therefore grain size increases but the strength of the ice skeleton decreases
- snow grains produced by this type of metamorphism range from immature facets to full blown depth hoar (not to be confused with surface hoar) and beaker crystals which are extremely weak, these grains are typically found at the base of the snow pack

Front 59

Melt Freeze Metamorphism

Back 59

Free (liquid) water can be introduced into the surface layers of a snowpack by melting (as a result of above freezing temperatures or solar radiation) or by rain-on snow events
- re freezing of this water produces melt freeze metamorphism whose end result is a grain type called a polygranular unit, melt freeze crusts may also form
- Metamorphism resulting from numerous melt freeze cycles such as occurs during spring produces corn snow
- In multi season snow, melt freeze metamorphism in conjunction with pressure metamorphism produces a very dense firn (or neve) transition to glacier ice

Front 60

Pressure Metamorphism

Back 60

- occurs only in multiseason snow because the pressure exerted by a significant depth (several m) of overlying snow is required for it to operate, the snow grains are deformed and rearranged by weight of the overlying snow
- operates in conjunction with melt freeze metamorphism over several seasons
- One other process is required to transform firn/neve into glacier ice: the refreezing of melt water percolating rom the surface down to the depths where temperatures are below freezing

Front 61

What are 5 physical properties of Snowpacks

Back 61

(1) Snow stratigraphy
(2) Snow strength
(3) Visco-elastic property
(4) Snowpack deformation
(5) Snowpack stresses

Front 62

Snowpack Stratigraphy (layering)

Back 62

- Thick layers: generally represent consistent conditions during one storm, when new snow crystals were the same type, wind speed and direction varied little, and temperature and precip rate were fairly constant
- Thin layers: reflect conditions between storms (ex. melt-freeze crust formed during fair weather, wind crusts formed during a windy period, surface hoar layers formed during a period of clear, calm weather) occasionally thin layers can form during storms, ex. rain crusts, ice layers from rain on snow event

Front 63

Snow Strength

Back 63

- greatly dependant on density
- high density snow has reasonably predictable strength properties like other common materials, and as such it has been researched for its suitability at low temp building material in polar regions
- physical properties of low density snow are extremely complex and its strength and fracture toughness are therefore difficult to predict, strength of such snow is mostly related to grain type and size (snow skeleton structure) and the effectiveness of the individual grains as levers, strength of low density snow may also be related to snow temp (lower temp = greater strength)

Front 64

Visco-Elastic Properties

Back 64

snow is a visco elastic substance meaning that on the application of stress it undergoes both viscous deformation and elastic fracture
- ratio of viscous deformation to elastic fracture at any given density is dependant on the rate and magnitude of stress application, snow temperature (lower temperature = greater elatic fracture), and grain type (ex. depth hoar does not deform viscously and therefore less stress application results only in elastic fracture)

Front 65

Snow Pack Deformation

Back 65

- snow pack on horizontal surface only has compressional force (gravity)
- snowpack on incline:
--Gravity split into compressive force and shear force (parallel to slope)
-- inclined snowpack exhibit creep and glide, this combination produces a down-slope motion in incline snowpacks which, especially in deep snowpacks, can exert very damaging forces of structures built on slops (fences, ski lift towers, power transmission towers)

Front 66

Snowpack Stress

Back 66

-Inclined snowpack exhibits shear stress and tensile stress in addition to compressive stress

Front 67

If snow grains are perfectly round and very small what metamorphism likely took place?

Back 67

- Equilibrium Metamorphosis
- water vapour is migrating from convex to concave parts of the grain and the end result is rounding

Front 68

Sintering

Back 68

When water vapour travels from convex to concave parts of the snow grain, creating necks
- water being deposited as ice

Front 69

What type of metamorphism produces polygranular units

Back 69

Melt-Freeze

Front 70

What type of metamorphism produces depth hoar, immature facets, and beaker crystals?

Back 70

Kinetic Metamorphism

Front 71

If the snowpack only survives 1 season what types of metamorphism can it undergo?

Back 71

Equilibrium, Kinetic, and/or Melt freeze

NOT PRESSURE - need multiple seasons for this

Front 72

Surface Hoar

Back 72

Below freezing equivalent of dew

Front 73

What 4 things determine snow strength?

Back 73

(1) Grain size and type
- Grain type, individual grains act as levers, more bending with larger grains therefore smaller grains generally give stronger snowpacks
(2) Ability to interlock with other grains
(3) Necks in between grains
(4) Temperature, sometimes lower temp = greater strength

Front 74

What 4 things does the viscous deformation and elastic fracture ratio depend on?

Back 74

(1) Magnitude of stress applied
(2) How quickly stress is applied (rate)
(3) Temperature, warmer = viscous, colder = fracture
(4) Grain Type (ex. depth hoar will not get viscous)

Front 75

What are the two possible meanings fr "water content of snow"?

Back 75

(1) Free Water Content: The amount of free (liquid) water within the snow matrix, can range from 0-25%
(2) Snow Water Equivilent: the depth of water produced of the entire snow cover were melted, extremely important parameter in water supply and flood prediction, as well as for other uses

Front 76

What ways is snow water equivalence obtained?

Back 76

(1) measurments of accumulated nowfall made by climate data collection networks
(2) snow course observations
(These two the SWE measured directly)
(3) snow pillows, remote sense, and satellite have proven promising as well

Front 77

What does the NRG balance equation (the one with all the Q's) tell us

Back 77

determines the amount of NRG available for melting it does not tell us the amount of melting (determined by M = Qm/(p x hf x B)

Front 78

What is the problem associated with using the snow surface NRG balance (even the simplified version) and what do we do about this

Back 78

- the relative importances of the fluxes change dramatically from place to place and with time
- even if they were constant certain fluxes (Qe and Qh) are very hard to measure
- as a result air temp is often used as a surrogate measure of all the fluxes which drive snowmelt

Front 79

What are 3 ways that melt water is routed to the stream channel

Back 79

(1) Infiltration capacity of soil exceeds rate of melt water percolation , all water enters the soil and moves to channel as subsurface flow
(2) Rate of meltwater percolation exceeds the infiltration capacity of soil (soil is frozen?) and water moves to channel as overland flow
(3) Infiltration capacity exceeds meltwater percolation rate and water enters the soil, soil water percolates downward and raises water table,w ater table intersects ground surface near base of hillside, saturated over land flow is produced, water moves into stream as overland flow and base flow

Front 80

What are three ways that snowmelt floods can occur

Back 80

(1) high rates of snowmelt --> largely due to advection effects, relatively rare
(2) Snowmelt occuring in conjunction with heavy rainfall --> combo in which usually snowmelt accounts from approx 30% of runoff, snowmelt again occurring as a result of advection effects
(3) Ice Jams -->floating river ice jams river channel causing flooding, common in snowmelt fed rivers which flow northward over significnt distances (lower reaches of river still frozen as snowmelt occurs upstream)

Front 81

What area 4 ways to increase snow water supplies

Back 81

(1) Forest Management
- snow accumulation and water yeild can bbe increased by forest cutting, interception and transpiration losses can be reduced without an increase in evap
-snow melt can be delayed by cutting patters which retain shade from trees but minimise long wave "back radiation" to the snow cover
(2) Agricultural Management
- Variety of techniques
- field fences, vegetative barriers, snow plowing, stubble managment, surface midifications
(3) Cloud Seeding
- purpose is to increase snowfall as well as to redirect it downward
(4) Surface Water Diversions
- Dams, Canals, ect. to redirect melt water

Front 82

What are 4 things that melt water percolation is complicated by

Back 82

(1) Layer structure of snowpacks
(2) vertical drainage channels develop early melt sequence
(3) Presence of below freezing layers deeper in snowpack early in melt season
(4) pulsing nature of meltwater "waves" produced by diurnal cycles of NRG input

Front 83

What are the two basic approaches to snowmelt/rainfall flood prediction

Back 83

(1) Long-term (probabilistic) flood prediction
- statistical estimates of the probability of flooding
- limitation is weather forecasting, can not say forsure
- need historical record of stream flow
- make assumption that flood potential of a river does not change over time
- would use this when building structures that need to withstand these floods
(2) Short term ("real time" flood predictions
- hourly/daily/weekly forecasts
- would be used for emergency planning
- required a runoff forecasting model, information needed on snowpack cover and rough estimates of melting rates, temperature, and cloud cover, rainfall