Fall08 Hydro Exam 1

Front 1

hydrologic cycle and anthropogenic effects...

Back 1

-most sensitive to changes in climate

-most perturbed natural system

-

Front 2

hydrologic equation

Back 2

Q = P -ET (change in S)

Q=discharge
P=precip
ET=evapotranspiration
S= storage (usually groundh2o)

Front 3

global water users

Back 3

7% municipal

23% industrial

69% agricultural

Front 4

water restrictions

Back 4

only on municipal

Front 5

mountains as water towers

Back 5

1. increased orographic precip (lifting over mtns)

2. increased % of snow precip

3. stored for 6-8 mo

4. lower ET

5. released in short time span

6. increased h2o quality

Front 6

when snowflake hits ground

Back 6

thermodynamically unstable

-- starts to round

--forms either round or facet
(form change due to vapor flux)
--ie dry metamorphism
1-equitemperature (destructive - destroying structure)
{{rounds grains so structural strength increases (ie strong snow layer)... increase in density

2.temperature gradient (TG)
--constructive (builds grains)
(kinetic growth.. .fast vapor transport
-density decreases -- weak snow layer
***Must have temp gradient of
10*C/m and density<350kg/m3

Front 7

weak layers of snow (=avalanche)

Back 7

facets (TG snow)

Front 8

avalanche -- stress equation

Back 8

stress = (m)(g)(sin theta)

m- mass
g= gravity
theta = angle of slope (snow)

Front 9

types of avalanches

Back 9

1.loose snow (point release)

2. slab (either soft slab or hard slab)

Front 10

loose snow avalanche

Back 10

tear drop shape

unconsolidated (not very dangerous

wet or dry

Front 11

water vapor movement in snow

Back 11

moves from small crystals --> large crystals....
...from convex to concave

.. from warm surfaces --> colder surfaces

**for any given temp, equilibrium vapor pressure is higher over convex than concave

**depositing vapor rises temp

TEMP GRADIENT <10*C/m
= equilibrium vapor pressure

TEMP GRADIENT > 10*C
= kinetic = faceting

Front 12

cold content equation

Back 12

cold content = (Ci)(h)(PsBAR)(changeTemp)

Ci=specific heat of ice
h = snow height
PsBAR = avg density of snow
change in Temp = TsBAR (avg snow temp) MINUS Tm (melting temp of snow {0*C}

Front 13

melt energy equation

Back 13

melt energy = change in F = advected heat = change due to rain

change in F = (Pw)(Cw)(changeT)(P)

Pw = density of water
Cw = specific heat of water
changeT = Tr(rain temp) MINUS Ts (snow temp)
P = ppt

Front 14

albedo =

Back 14

Kin / Kout

Front 15

longwave emission

Back 15

emissivity (SB constant) Temp(K)

Front 16

Q aka

Back 16

Q = dQ/dt = changeM = internal energy =
"MELTING ENERGY"

Front 17

calorie to joules

Back 17

1 cal = 4.184 joules

Front 18

water budget equation

Back 18

dVbar/dt =

ZERO =

(pBar + rBar(si) + rBar(gi)) - (rBar(so) + rBAR(go) +ETbar)

p = avg precipt
si = surface h2o inflow
so = surface h2o outflow...
g = groundwater
et - et

...............

***Pbar = r(bar)s + ETbar

Rs = surface h2o outflow --- RUNOFF

Front 19

residence time =

Back 19

Tr = V / I

residence time = volume / inflow

Front 20

max density of h2o at

Back 20

4*C

Front 21

regression tells you

Back 21

r2 -- how much x explains the variance in y

p-vale -- tells if slope of line different the zero

*NOT IF SIGNIFICANT

Front 22

paired ttest

Back 22

use to test hypothesis about equivilancy of sample
(significantly different or equivilant?)

t-crit = value found when using significance value and df on table

t-stat> t-crit = significantly different

Front 23

formation of precip

Back 23

air must contain water vapor

vapor must condense

(condensation requires cooling of air and condensation nuclei

Front 24

RH

Back 24

relative humidity

amt of water vapor in air : max water vapor air can hold
x100%

Front 25

SVP

Back 25

saturation vapor pressure

MAX amt of water vapor air can hold

(increases with temp)

Front 26

dew point

Back 26

temp at whihc air reaches saturation

(RH = 100%

*high dew pt = h2o vapor contemnt of air is HIGH
(ie requires higher temp to saturate

Front 27

increase RH by..

Back 27

adding moisture OR cooling air mass

Front 28

adiabatic cooling

Back 28

uplifted air expands -- then cools (no loss of heat)

== due to air masses converging / convection / orographic

Front 29

convergence
v
convective

(air temp changes)

Back 29

Convergence --
air goes from high to low pressure

convective --
air heated over warm land
--rises
**heating at surface***

Front 30

measure precip

Back 30

amt (depth)

intensity (rate ... mm/hr)

duration (length of spell)

Front 31

problems w rain gages

Back 31

misread

instrument limitationms

gage placement

wind eddies

Front 32

Hyetograph

Back 32

graph of rainfall rate v time @ single gage

(BAR CHART)`

Front 33

SCA stands for=

Back 33

snow coverred area

Front 34

methods for averaging rainfall

Back 34

1. arithmatic (not weighted)

2. thiessen polygon

3. isohyetal maps (contour)

4. hypsometric

Front 35

thiesson polygons
(measure avg precip)

Back 35

split area around each gage into polygons

values weighted by how big area is

Front 36

isohyetal maps
(measure avg precip)

Back 36

(contour map)

weighted `

Front 37

hypsometric method
(measure avg precip)

Back 37

1. plot precip v elevation

2. linear regression

3. slope of regression line = OROGRAPHIC EQUATION

4. hypsometric curve

Front 38

interannual variability

(precip)

Back 38

std dev of precip values

Front 39

"exceedence probability"

Back 39

probability that the event will be equalled or exceeing in time period

Front 40

return interval / return period

Back 40

avg length of time between flows of a given magnitude

RI = 1/EP (exceedence probability)

ie if RI = 100 yrs, it has a 1% EP of returning each year

Front 41

need for nucleation (of snow formation)

Back 41

water vapor

+nucleus

+TEMP LOWER THAN 0*C

+Saturation

Front 42

snowfall formation

Back 42

watervapor +nucleus+ T<0*C + saturation

--> Nucleation

--> ice crystal
(sublimation growth)
--> snow crystal

CONTINUED GROOWTH :
RIMING ; SUBLIMATION ; AGGREGATION

Front 43

Temp of SNow Pack (2options)

Back 43

1. temp gradient (base of pack usually 0*C)

2. NO TEMP GRADIENT
(isothermal)

diurnal temp gradient = gradient switches between day and evening

Front 44

metamorphism of snow occurs when

Back 44

--snow close to melting temp

--thermodynamically unstable (high surface to volume ratio .. free energy)

--compaction due to overlying layers

Front 45

2 types of metamorphism

Back 45

1. DRY

2. WET

Front 46

DRY METAMORPHISM

Back 46

no liquid h2o

temp <0*C

solid state in equilibrium with vapor

**Driven by vapor movement in pores

Front 47

WET metamorphism

Back 47

liquid h2o present

temp =0*C

Front 48

vapor pressure gradient

Back 48

causes vapor movement (which causes dry metamorphism)

Controlled by:
1.TEMP
--warm holds more vapor than cold area
(flows from cool to warm)

2. RADIUS OF CURVATURE
-increase radius = increase vapor density

3. GRAIN SIZE
lower grainsize = increase radius of curvature = increase vapor density

Front 49

2 types of dry metamorphism

Back 49

1. Equitemperature (ET)

2. TEmperature Gradient (TG)

Front 50

Equitemperature (ET)

(dry metamorphism)

Back 50

-DESTRUCTIVE
-reduces surface free energy to stable state

-depends mostly on radius of curvature

-decrease surface:volume ratio
= DENSITY INCREASE
= INCREASE STRENGTH

(**rounds snow grains!**

Front 51

Temp Gradient (TG)

(dry metamorphism)

Back 51

builds angular faceted grains

decreases density

decreases strength

TEMP GRADIENT MUST BE at or above 10*C/m

MUST HAVE SNOW DENSITY OF < 350kg/m3
(to maintain sufficient vapor flow

Front 52

wet snow metamorphisms

Back 52

melting and refreezing -- large bonded clusters

Front 53

intensity of rainfall

Back 53

intensity = (PPT depth) / (duration hrs)

Front 54

conduction important when

Back 54

density greater than 350 kg/m3

Front 55

rounds or facets at equilibrium?

Back 55

rounds

Front 56

TG snow (IE KINETIC SNOW)

Back 56

= early season

Front 57

energy transfer methods

Back 57

1. radiation

2. conduction
(molecule to molecule)

3. convection
(mixing)

4. Advection
(transfer by mass transport ... ie rain)

Front 58

Absorbtion = Emissivity

Back 58

Reflectance =
1 - emissivity

Front 59

reflectance of sun compared to snow grain radius

Back 59

smallest radius = most reflective

Front 60

albedo decreases

Back 60

with time

Front 61

turbulent energy transfer

Back 61

= sensible and latent heat flux

--function of wind / temp / humidity

**for intense snowmelt to happen need large turbulent E transfer

dominates energy transfer on cloudy days

(small SW exchange .. and LW usually cancel eachother out -- ie RAD DOESN't Effect)

Front 62

latent head (LE or Qe)

Back 62

condensation or sublimation
(phase change)

-function of Lv (latent heat of vaporization)
--vapor pressure gradient
--turbulence

**if vapor pressure increases with height water vapor condenses on snow (gains E)

if vapor pressure decreases with height h2o vapor sublimated from snow
(ie dryer with height)
(Lv (latent head of vaporization) lost)

Front 63

Saturation Vapor Pressure of melting snow cover (0*C) =

Back 63

~ 6mb

Front 64

"vapor pressure deficit"

Back 64

drying power relative to saturated surface

(if vapor pressure in air VERY low = deficit
== SUBLIMATION)

requires dry air and high winds (turbulence)

*loss of h2o in high elevations often due to this

Front 65

sensible head (H)

Back 65

convection

function of spec heat of air
-air / temp gradient
-turbulence

**if air temp increases with height heat is convected to the snow

Front 66

HEat advected by precip (change F)

Back 66

(2ways)

1. rain on melting snowpack
changeF = 4.2TrPr
Tr= rain temp
Pr = depth of rain

units [kJ /m2d]


2. rain on cold snow pack (<0*C) rain refreezes
(relesing its latent heat of fusion (Lf)

Lf = given

Front 67

snopack "ripens"

Back 67

= becomes isothermal at 0*C
... snow melt can occur as long as energy supplied and pack doesn't cool

Front 68

regression analysis

(snow modeling)

Back 68

-provides estimated total discharge @ gage site

--requires representative site (swe measurements)
---+ annual / seasonal discharge @ gage site

disadvantage -- need long term records (10+yrs)
--no info on magnitude or timing of snowmelt
--can't extrapolate past range of measurements

ADVANTAGE:
-- estimates total discharge from basin
-- good for mgmt decisions
--simple
--don't need much dada

Front 69

temperature - index methods

(snow modeling)

Back 69

-based on idea that chagnes in air temp provide index of snow melt

++ air temp commonly measured data

1. degree day factor equation
2. snowmelt runoff model (SRM)

Front 70

degree day factor equation

(temperature index method)

Back 70

M = Mf (Ta - To)

M = snowmelt

Mf = degree day factor
(mm / *C / day

Ta = air temp (*C)

To = threshhold (where snow melt starts --- = 0*C)

Front 71

SRM: snowmelt runoff model


(temperature index method)

Back 71

Q = [(CaTS) +P]A

Q=discharge
C = runoff coefficient (runoff efficiency)
a = degree day factor
T = #of degree days

S = ratio of snow cover : uncovered

P = new precip
A= area



BENEFITS OF SRM
-only a few variables to be measured

Front 72

Energy Balance Models

Back 72

run on MEASURED DATA

1. precipiation submodel
... storage and spacial distribution of snow and SWE
___hard to find tools to measure SWE

2. energy balance
(Q= R+G+H+LE+A+dQ/dt

3. snow pack model
(difficult bc don' tknow abt liquid retention / movement... loose track of snow once melted)

4. snow depletion model
(must keep track of SCA and SWE
__too hard to measure changes in SWE over time

Front 73

Conservation of Mass equation

Back 73

conservation of mass -- often called "water balance" or "water budget"

the conservation of mass for a compartment is:: the time rate of chagne of massstored within the compartment is EQUAL to the difference between inflow and outflow

dV/dt = I - O

inflow rate - outflow rate = volume change /time

Front 74

Residence Time

Back 74

Tr = V / I

volume / inflow

(inflow and outflow identical

Front 75

xbar

Back 75

sample mean

Front 76

x

Back 76

individual measurement

Front 77

V

Back 77

variance

(how spead out data is)

Front 78

s

Back 78

standard deviation

= measurement of variability

Front 79

SE

Back 79

standard error

the variability that can be expected in the means of the samples

Front 80

"catchment efficiency"

Back 80

(ie runoff efficiency)

Ru/PPT

Front 81

tstat < tcrit

Back 81

no significant difference

Front 82

calculating s

Back 82

(Xi - Xbar)^2
(for each ind measurement)
-->SUM ALL

divide by n-1

take square root

Front 83

CV

Back 83

coefficient of variation

CV = s / Xbar x100%

Front 84

SE

Back 84

standard error

SE = s^2/n

take square root

Front 85

df

Back 85

degrees of freedom

n - 1

Front 86

orographic equation estimates

Back 86

precipitation for each elevation zone

Front 87

determine amt of heat from a rainfall

Back 87

changeF = PwCw(Tr-Ts)P

Pw = density of snow
Cw = specific heat of liquid h2o

Tr=rain temp
Ts = snow temp

P = precip amt (length / time)

Front 88

equation for melting snow

Back 88

change E = Pw Lf d

Pw = density of snow

Lf = latent heat of fusion

change in E = change in energy

d = depth (ie melted snow)

Front 89

Lf

Back 89

latent heat of fusion

Front 90

d

Back 90

depth

Front 91

Pw

Back 91

density of snow

Front 92

outgoing SW rad ...

Back 92

Kout = (alpha)(Kin)

ie albedo x Kin

Front 93

energy change equation for melting snow

Back 93

change E = Lf Pw Vw

Lf = latent heat of fusion (given

Pw = density of water

Vw = volume of water

((solve for depth))