Fall08 Hydrology Exam2

Front 1

most important soil moisture parameters in agriculture

Back 1

field capacity
&
permanent wilting pt

Front 2

field capacity

Back 2

maximum h2o content without drainage

(before gravity drainage starts

Front 3

permanent wilting pt

Back 3

water content when water held too tightly for plant uptake

(unavailable to plants)

Front 4

soil moisture cycle

Back 4

fall: rainfall recharge

winter: MAX soil storage

spring: some evaporative loss

summer: most depleted

Front 5

porosity equation

Back 5

n = Vv / Vt

Vv = volume voids
Vt = total unit volume

n = porosity

Front 6

porosity expressed as

Back 6

percent or
decimal fraction

Front 7

porosity (rock v soil)

Back 7

rocks lower porosity than soil

(less pore space in rocks)

Front 8

porosity and hydraulic conductivity

(n and K)

Back 8

higher n usually = higher K

higher porosity = higher hydraulic conductivity

[[hydraulic conductivity = the ability of medium to transmit fluid]] --{depends on fluid's properties and porous medium's properties}


**CLAY SOILS EXCEPTION**

Front 9

when does higher porosity not result in higher hydraulic conductivity

Back 9

CLAY SOILS

higher porosity doesn't increase clay's ability to transmit fluid

Front 10

infiltration

Back 10

movement of water into soil

Front 11

infiltration varies with time

Back 11

varies with TIME
as a function of:
-precipitation intensity
-changes in soil tension
-hydraulic conductivity
with changing soil moisture

Front 12

infiltration varies with (not time)

Back 12

previous moisture conditions

slope

Front 13

precip rate < infiltration rate

Back 13

all water that reaches surface infiltrates

Front 14

precip rate > infiltration capacity

Back 14

get depression (detention) storage

Front 15

if ground is sloping depression storage..

Back 15

depression storage may be small

-- overland flow will begin soon after depression storage filled

Front 16

infiltration if ground is already saturated
("saturated from below")

Back 16

depression storage occurs immediately
if W(t)>Fc(t)

Front 17

measuring infiltration
(pt measurements)

Back 17

1. ring infiltrometer

2. dbl-ring infiltrometer

3. observing soil water changes

4. sprinkler plot studies

Front 18

measuring infiltration
(over an area)

Back 18

1. use stream discharge records & precip records

2. rain gage data used to determine amt of rain that fell on drainage basin

3. analyze hydrograph (determine amt of runoff)
precip - runoff = infiltration

Front 19

factors influencing infiltration

Back 19

1. permeability of surface material

2. slope

3. antecedent (previous) moisture conditions

4. human activities

Front 20

"desertification"

Back 20

loss of productive / marginally productive land

due to poor land use practices

**soil becomes dry

**loss of vegetation

**reduced soil fertility

**hardening of soil

--> infiltration decreases

--> erosion increases

Front 21

causes of desertification

Back 21

-overgrazing
-woodcutting
-poor farming practices
-poor water management on cultivated lands
-climate change

over irrigation...

Front 22

over-irrigation

Back 22

can lead to salinization of soils
--salts precipitate from evaporation irrigation water

--contributes to DESERTIFICATION

Front 23

F

Back 23

amount of infiltration

(cumulative infiltration over time period)

Front 24

f(t)

Back 24

infiltration rate

f(t) = dF/dt
(change in amt of infiltration over change in time)

**depends on w(t)

Front 25

w(t)

Back 25

water input rate

(snowmelt or
precipitation intensity)

Front 26

f -sub-c (t)

Back 26

maximum rate at which infiltration can occur

Front 27

infiltration rate
f(t)

Back 27

HIGH if soil initially dry

if w(t) (water input rate) is constant,
f(t)decreases to near-constant value (~Ksat)

Front 28

K

Back 28

hydraulic conductivity
in velocity units

--describes soil in cylinder w/ water moving thru it

Front 29

darcy's law valid for

Back 29

groundwater flow in any direction

Front 30

hydraulic conductivity (K) is function of

Back 30

fluid and medium

Front 31

K relationships

Back 31

K increases with increasing h2o content

K at max at saturation

saturated K depends strongly on grainsize

Ksat depends on soil texture

Front 32

darcy's law based on

Back 32

experiment
(empirical)

Front 33

pressure developes in groundh2o when

Back 33

it flows thru porous mediums

Front 34

"fluid potential"

Back 34

water flow due to potential

= the mechanical energy / mass fluid

*related to elevation / pressure

Front 35

fluid flow (happens due to fluid potential)

Back 35

-must overcome water-soil friction

-must transfer mechanical energy -> thermal energy

-flows from higher mechanical energy to lower mechanical energy

Front 36

"bulk density"

Back 36

density of a dry sample

Front 37

"porosity"

Back 37

volume of voids : volume of solids
(ratio)

Front 38

"volumetric water content"

Back 38

water volume: soil volume

Front 39

"soil wetness"

Back 39

degree of saturation

*the proportion of pores that contain water

Front 40

"capillary fringe"

Back 40

the pt when air begins to appear in the soil pores

Front 41

in unsat,
hydraulic conductivity v water content

Back 41

hydraulic conductivity increases with increasing water content

... then levels off and becomes constant (when soil is saturated)

Front 42

what's darcy's law used for

Back 42

calculating the rate of floow
in a given direction

based on the resistence of the medium and the applied gradient

Front 43

direction of flow
(according to darcy's law)

Back 43

flow occurs in direction of decreasing hydraulic gradient

(goes from high to low hydraulic gradient)

(-) hydraulic gradient = water is moving up

Front 44

(-) hydraulic gradient

(h2o movement)

Back 44

water is moving up

Front 45

(+) hydraulic gradient

(h2o movement)

Back 45

water is moving down

Front 46

"groundwater"

Back 46

subsurface water below the water table
--in saturated soil and geologic formations

Front 47

groundwater
(geology /
chemistry /
hydrology /
technology)

Back 47

GEOLOGY:
-flow (qualitative)
-fluid mechanics
-groundh2o behaves as field

CHEM:
-contaminants,
-dating groudh2o

HYDRO:
-flow
-applied math

TECHNOLOGY:
-drilling / maintaining wells
-sampling
-logging

Front 48

"aquifer"

Back 48

saturated permeable geologic unit
(can transmit sign. amt of h2o)

Front 49

"aquiclude"

Back 49

saturated geologic unit that canNOT transmit sign. amt of h2o

Front 50

"aquitard"

Back 50

less permeable geologic bed

Front 51

thruflow occurs

Back 51

in unsat zone
(above h2o table)
(below surface)

Front 52

artesian well

Back 52

when confined aquifer in saturated zone has well
(well punctures into aquifer below water table)

Front 53

water-table well

Back 53

well in the water table

-- height of water = height of capilary fringe

Front 54

cone of depression

Back 54

depression of water table around well (in h2o table)

Front 55

"mass density"

Back 55

curved p

(1000..)

Front 56

"weight density"

Back 56

greek y

(weight per unit volume)

= curved p * gravity

Front 57

Specific Gravity (G)

Back 57

ratio of (something's)density to water

Front 58

viscocity

Back 58

greek u

(property of liquid's resistence to motion)

Front 59

compressability

Back 59

greek B

= stress (fluid pressure) / strain properties

Front 60

"piezometers"

Back 60

measure hydraulic head in aquifer

-open at bottom

-intake of h2o only

Front 61

"specific storage"

Back 61

volume h2o released from aquifer due to unit
DECLINE IN HYDRAULIC HEAD

Front 62

"storativity"

Back 62

unit h2o released by aquifer per unit decline hydraulic head NORMAL TO SURFACE

Front 63

ET includes

Back 63

1. E from surface h2o
2. E From land surfaces
3. E from soil
4. SUBLIMATION snow / ice
5. TRANSPIRATION

Front 64

RO =

Back 64

runoff =

P - ET

Front 65

evap losses from

Back 65

man made reservoirs huge

Front 66

errors in rainfall / RO measurements often due to

Back 66

ET

Front 67

measuring ET

Back 67

difficult

.. usually models used

Front 68

evap models based on

Back 68

1. water balance
2. energy balance
3. mass transfer
4. combo approach

Front 69

evap pans

Back 69

-measure free water evap

-moniter precip (depth in pan)

E = W - (V2 - V1)

evap = precip (total depth) - change in depth

"pan coefficients" = correction factors to convert pan data to lake estimates

Front 70

"pan coefficients"

Back 70

correction factors for evap pans to convert data to lake estimates

Front 71

bowen ratio

Back 71

H / LE

sensible heat flux / latent heat flux

Front 72

lake evap

Back 72

function of wind speed, temp, humidity gradient

-related to solar energy

**measured by
1. mass transfer,
2. energy budget
3. pan evap

Front 73

green-ampt equation describes

Back 73

infiltration into dry soils
... h2o progesses downward -- sharp wetting front seperates unsat soil below from sat soil above... this front progresses downward as infiltration occurs

- assumes wetting front infinitely sharp (horizontal)
*so the flux in the sat upper portion equals the infiltration rate

((IE the hydraulic gradient is uniform))

Front 74

green ampt equation

Back 74

i = -Ks [[(-pressheadf + 0)/Lf ]+1]

i = infiltration rate (= spec discharge)

Ks = sat conductivity

pressure head symbol sub f = pressure head at wetting front

Lf = depth to the wetting front

Front 75

most imp factors governing infiltration of water

Back 75

1. precip rate

2. K of soil (hydraulic conductivity)

3. initial soil moisture

4. slope / roughness of surface

Front 76

soil moisture affects

Back 76

1. soil moisture tension

2. K (hydraulic conductivity)

3. how much storage available

Front 77

as water moves deeper (with infiltration)

Back 77

the ratio of

soil moisture tension at wetting front
:
depth of the wetting front

becomes smaller bc total volume h2o is distributed over a greater depth (and i decreases)

*as ratio becomes very small
i (or f(t)) approaches Ksat

Front 78

"logging for water"

Back 78

WANT: to log to increase snowmelt

RESULTS:
when trees removed:
-more snow collected in the openings
-more h2o ran off into streams in spring

Front 79

why logging increases snomelt

Back 79

snow that is intercepted by trees sublimates (turns directly from snow to h2o vapor) -- never reaching the ground

Front 80

prob with logging for snowmelt

Back 80

it doesnt work everywhere

when it does work:
-increased RO pollutes streams with sediments (degrades fish habitat)

-the increase in RO is only measurable in spring -- new reservoirs need to be built to capture extra h2o

Front 81

eddy flux instrument

Back 81

measures latent heat

(knowing latent heat can convert to mm sublimation)

** can have instrument below and above forest canopy**
---can measure sublimation below and above
--ie canopy sublimation and
below canopy sublimation

Front 82

precip and sublimation

Back 82

increase precip = increase sublimation

canopy sublimation greater than snowpack sublimation

Front 83

eddy covariance systems indicated..

Back 83

substantial loss of winter snow accumulation by SUBLIMATION

(canopy more than snowpack)

**more than 100% precip lost to sublimation

Front 84

max sublimation occured

(eddy covariance experiment)

Back 84

immediately after snowmelt
-driven by canopy interception

*HIGH LE flux

Front 85

below canopy sublimation driven by

(eddy covariance experiment)

Back 85

driven by high H (sensible heat) gradients
--- warm canopy pumping heat into cold atmosphere

high H gradient ==> high spec humidity gradient

-RH (relative humidity) = 100% at snow surface
-RH much lower above snow surface
-----> lead to high snowpack sublimation

Front 86

sublimation higher when intercepted by veg than on the ground ...

Back 86

bc leaf surface is higher temp

-leaf = greater surface area

-trees radiate longwave

-higher air temp around canopy
-- INCREASE IN SAT VAPOR PRESSURE

Front 87

decreasing interception by cutting trees =..

Back 87

increases volume of snowpacak

increases water yield

Front 88

the more trees removed...

Back 88

the greater the SWE increased

(snow water equivilant)

Front 89

as size of opening increases
(logging experiment)

Back 89

its snow trapping efficiency decreases
(to the pt where there is a net loss)

--- due to increased wind scouring and sublimation losses

Front 90

influence of wind in logging experiment

Back 90

more wind = less efficient

- SWE greatest on leeward side of clearing
- SWE least on windward side of clearing

Front 91

flow increased most...

(logging experiment)

Back 91

during wet years

(opposed to droughts)

Front 92

(-) of logging for snowmelt

Back 92

-increases in discharge = increase erosion / flooding

-need additional reservoirs
to store water for low flows

-logging related activities (including road construction..) = increase erosion and Sedimentation


NUTRIENT LOADING:
-increase in nutrient loading
-increase in DOC
-increase in ion concentrations

increases in nitrate concentrations
..due to
((reduced nutrient uptake bc less vegetation))
((nutrient release from decomp of trees))
((increased soil N transformations))

-remove habitat
-maintanence required to maintain yields ($$$)

--h2o flow off trees increases with age..

Front 93

debate: "dual purpose of logging"

Back 93

1. increase water yeild
2. reduce fire risk

(but logging at high elevations [[not high fire risk]]
-wont reduce high fire risk of low elevations

Front 94

higher elevation = less ET

Back 94

less trees at high elevation

colder air temps with elevation

Front 95

"PBL"

Back 95

planetary boundary layer
(layer of atmosphere where air motion strongly influenced by interaction with earth surface)

**CHARACTERIZED BY TURBULENT AIR FLOW**

- imagined as horizontal flow of mult rotating eddies

(each eddy has 3d component including vertical wind component)

Front 96

eddie covariance experiment
uses

Back 96

IRGA
-IR gas analyzer

-sonic anemometer

*measures evap flux and LE flux

Front 97

each parcel of air has a particular..

(eddy covariance experiment)

Back 97

1. trace gas concentration

2. temperature

3. humidity

Front 98

vertical flux

(eddy covariance experiment)

Back 98

eddie flux:
F = (density air)(w)(s)

latent heat flux (on eq. sheet)

Front 99

"footprint"

(eddy covariance experiment)

Back 99

'field of view'

-area that contains the sources / sinks contributing to a certain measurement pt

(reflects surface's influence on the measured turbulent flux)

Front 100

assumption

(eddy covariance experiment)

Back 100

pt measurements represent upwind area

footprint contains only area of interest

flux is fully turbulent
(vertical transfer done mostly by eddies)

Front 101

"bulk density"
+ eq

Back 101

bulk density is the density of DRY SOIL

Pb = Mm / Vs

bulk density = mass of dry matrix / total soil volume

Front 102

porosity eq

Back 102

pososity = void space / total volume

(Va + V) / Vs

air volume + water volume / total soil volume

= 1 - (bulk density / particle density)

Front 103

moisture content (theta)

eq

Back 103

= Vw / Vs
volume water / soil volume

= (Mswet - Msdry) / (Pw*Vs)

Front 104

soil wetness
ie DEGREE OF SATURATION
(S)
eq

Back 104

moisture content / porosity

= volume water / (volume air + volume water)

Front 105

capillary fringe defined as

Back 105

pt at which air begins to appear in soil (VERY CLOSE to saturization -- if not completely saturated)

Front 106

moisture content (PWP)

eq

Back 106

PWP =

(porosity)*{[abs value pressure head -sub ae]/1500}^1/b

pressure head -sub ae =
air entry tension

b = describes moisture curve

Front 107

how does K change with increasing moisture content

Back 107

increasing moisture content
= increasing hydraulic conductivity

(eventually levels off to constant Ksat (K under saturated conditions)

Front 108

the pt of saturation:

Back 108

when moisture content no longer increases (stays constant) with increasing pressure head

Front 109

h =

Back 109

hz + hp

elevation head + pressure head

Front 110

hz

Back 110

elevation head

= z - z0
(elevation minus the arbitrary datum)

Front 111

hp

Back 111

pressure head

= water pressure / weight density of h2o

Front 112

(-) hydraulic gradient means water is moving

Back 112

up

Front 113

green-ampt equation

Back 113

i = - Ks [{(-pressure head sub f) / Lf}+1]

i = infiltration rate

Ks = saturated conductivity

Presshead f - pressure at wetting front

Lf = depth to wetting front

Front 114

I

(green-ampt)

Back 114

total infiltration

= Lf * change moisture content

Lf = depth to wetting front

change in moisture content = saturated - initial

Front 115

time to ponding related to initial miosture content

green-ampt

Back 115

time to ponding decreases with increasing initial water content

Front 116

low initial moisture content v
high initial moisture content

the rate the wetting front increases ...

Back 116

wetting front increases faster in soils with high initial moisture
(fewer voids to fill --- must fill all voids b/c wetting front is "SATURATED ZONE"

Front 117

"time of ponding"

green-ampt equation

Back 117

when the top of the soil becomes saturated

Front 118

after 'time of ponding'

Back 118

ie after top of soil = saturated,

the rate of infiltration increase decreases slightly

Front 119

hydraulic conductivity :

aquiclude v aquifer

Back 119

aquifer = high hydraulic conductivity

aquiclude - low hydraulic conductivity

Front 120

Unconfined aquifer:

what is pressure head at water table?

Back 120

pressure head is 0 @ water table

-- hydraulic head = the elevation head
(ie h = z +0)

Front 121

transmissivity

Back 121

T = Ksat*b

b= thickness of aquifer

Front 122

when comparing heights of the water table

for spec discharge

Back 122

q = -K dh/dl

q = -K * [(Pressure2 + z2) - (pressure1 + z1)]/l2-l1

**CAN ELIMINATE PRESSURE HEAD bc PRESSURE HEAD = 0 at height of water table

Front 123

simplified hydraulic equation

Back 123

Qstream = PPT - ET

Front 124

area

Back 124

A = pi*r^2

Front 125

volume

Back 125

V = A * Depth

Front 126

mass =

Back 126

m = pv

mass = density * volume

Front 127

change in depth (for pan method of evap)

evaporation?

Back 127

change in volume / AREa

evaporation is in change in depth / time

Front 128

LE flux from pan method

Back 128

LE = (change depht / change T)*(latent heat of evaporation)

(Levap given)

Front 129

pan technique used for basin

Back 129

E/A = (d1 - d2)*(fpan)

evap / basin area = (depth 1 - depth 2) * (pan coefficient)

Front 130

energy balance

to calculate ET

Back 130

LE = K + L + Aw - G - H - changeQ/changeT

latent heat flux = net radiation + water advected energy - heat loss due to ground - sensible heat loss to atms - heat loss from storage

simplified:
LE = R - H

*replace H w/ bowen ratio*

LE = R - LE(H/LE)

LE + LE(H/LE) = R

LE*(1+ H/LE) = R

LE = R / (1+H/LE)

Front 131

"stream gauging"

Back 131

measuring stream flow
(discharge)

Front 132

velocity of stream varies with

Back 132

width and depth across stream

-fastest in middle - less friction

Front 133

measuring stream surface velocity

Back 133

float method

time orange for 30m

Front 134

measuring stream discharge (accurate)

Back 134

velocity area method

Front 135

avg velocity of stream is

Back 135

0.6x total depth from SURFACE

Front 136

K
sat v unsat

Back 136

K constant in saturated
(depends on grain size)
*hydraulic conductivity highest at least depth in saturated zone ... less compaction

unsat
K varies with moisture content
**less moisture = more tension = h2o flows (is sucked) faster = greater hydraulic conductivity

Front 137

springs

Back 137

when water table (sat zone) hits a dip in the topography

Front 138

water flows from
(tension)

Back 138

low tension to high tension

Front 139

field capacity

Back 139

available water for plants

PWP < availh2o < FC

Front 140

artesian system

Back 140

confined aquifer -- boundaries don't move -- pressure is released

Front 141

cone of depression

Back 141

occurs with unconfined aquifer

-- depression in h2o table

--- results in velocity increasing with proximity to well

Front 142

three types of ET measurements

Back 142

1. Pan Approach (DIRECT MEASURMENT)

2. Energy Balance Approach -- MEASURES LE
---eddy covariance
---aerodynamic profile
--- bulk transfer
---bowen ratio

3. Water balance equation
- solve for ET
**most common
**least precise

Front 143

best measurement of ET?

Back 143

eddie covariance

-over large area
-integrated (not just pt measurement)
-measures in 3d
-measures at high frequency
-low margin of error

-----disadvantage---
-a lot of interpreting after data collection

Front 144

laminar flow

Back 144

viscous forces dictate the nature of the flow

--maj of groundwater flow since pore spaces small

Front 145

cone of depression equation

Back 145

Vcone = Vpumped / Sy

Sy = specific yield

Front 146

pan evap -- for basin

Back 146

E/A = (d1 - d2)fpan

Front 147

measures hydraulic head for UNSAT

Back 147

tensiometer

Front 148

measures hydraulic head for SAT

Back 148

piezometer

Front 149

each parcel of air
has
(eddy)

Back 149

1. trace gas concentration

2. temperature

3. humidity

Front 150

K independent of pressure
v
K function of pressure

Back 150

SAT - K independent of pressure

UNSAT - K and moist.content function of pressure

Front 151

K at max

Back 151

saturated

Front 152

pressure head > 0

Back 152

saturated

Front 153

pressure < 0

Back 153

unsaturated

Front 154

PWP eq

Back 154

PWP = porosity * [(air entry tension)/15000]^1/b

Front 155

pt of saturation

(K compared to moisture content

Back 155

K no longer changing with changes in h2o content

Front 156

hp

(pressure head component of hydraulic head)

Back 156

hp =

p / Yw

p = water pressure
Y(greek)w = WEIGHT DENSITY h2o

Front 157

"thruflow"

Back 157

unsat zone

Front 158

perched aquifer

Back 158

--> SPRINGS

above impervious layer (perched h2o table and aquifer lay above main h2o table)

Front 159

greek u

Back 159

dynamic viscosity

Front 160

greek v

Back 160

kinematic viscocity

greek u / p

Front 161

greek B

Back 161

compressability

Front 162

k

Back 162

permeability

= K(greek u) / pg

Front 163

water level in unconfined aquifer

Back 163

= water table

= hydraulic head (elevation + press head)

Front 164

wind etc - to measure EVAP

Back 164

E = Ke * Va * (e.s - e.a)

Ke = turbulence factor

Va = wind speeed

e.s = vapor pressure at saturated surface of h2o

e.a vapor pressure above water

Front 165

bulk transfer

measure evap

Back 165

E = 1.26 x 10^-6 Va (e.s - e.a)

Va = velocity of air (WIND SPEED)

e.s = vap pres in saturated zone at water surface

e.a = vap pres above surface

****PAREMETERS VARY GREATLY WITH TIME (don't do more than a day at a time)

Front 166

rate LE transfer
and
fick's law

Back 166

LE = densityh2o * latent heat of vaporization * evaporation

---> put into fick's law
E = Ke * Va * (e.s-e.a)
.....

LE = (density water)(latent heat vaporization) (turbulence) (air velocity) (vap pres sat - vap pressure above)

Front 167

bowen ratio

Back 167

H / LE

Front 168

adv / disadv for whole energy balance equation

Back 168

+ -- using bowen ratio elimates need for wind speed

--- need lake temp / inflow / outflow / volume

Front 169

i must equal

Back 169

negative of the total infiltration over time

((-) flux means down!!!)

i = - dI/dt
= - change moisture content * dLf/dt

(dLf = depth of wetting front)
I = Lf*change moisture content


... infiltration = Ksat * [ (-presshead @ front * change moisture content)/Lf}]

Front 170

water table aquifer

Back 170

unconfined aquifer

-- water table is binding surace on top

--PUMPING WELL DROPS THE H2o table

Front 171

confined aquifer

Back 171

artesian aquifer

confined by aquiclude
(overlain by it...)

water is UNDER PRESSURE

piezometer measures water pressure in aquifer

*pump w/o decreasing h2o table -- pressure forces water up well above h2o table

Front 172

name for unsat zone

Back 172

vadose zone

*between surface and water table

Front 173

pore spaces partly full

Back 173

vadose

Front 174

"soil moisture"

Back 174

water in vadose zone

-- goes to ET and to recharge ground

Front 175

capillary tension

Back 175

h2o withdrawn, air enters pores
-air-h2o interface presenet

h2o pulled up inside of tube due to NEGATIVE PRESSURE

(pulled up from pressure head of 0-- like sponge in bowl h2o)

"capillary pressure head" = applied neg pressure