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practice > Hydrology > Flashcards

Hydrology Flashcards

1
Q

Synder Method

A
  1. Observe storm
  2. Form standard UH and find Ct and Cp
  3. Use Ct and Cp for similar catchment
  4. Construct hydrograph for design storm (tR, tpR, tb, W50, W75)
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2
Q

tR

A

Required rainfall duration [h]

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3
Q

tpR

A

Required time to peak runoff [h]

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4
Q

qpR

A

Required peak runoff [m3/s/km2/cm]

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5
Q

tr

A

rainfall duration [h]

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6
Q

tp

A

time to peak runoff [h]

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7
Q

qp

A

peak runoff per unit basin area per unit of rainfall [m3/s/km2/cm]

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8
Q

Ct

A

lag coefficient

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9
Q

Cp

A

peak coefficient

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10
Q

W50 and W75

A

time width at 50% and 75% peak flow

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11
Q

tb

A

base time [h]

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12
Q

Placement of W50 and W75

A

1/3 before peak, 2/3 after peak

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13
Q

SCS Dimensionless Hydrograph Process

A
  1. Find Tp and qp for the design storm
  2. Plot Tp, qp (and tr if given)
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14
Q

Limitations of synthetic unit hydrograph

A
  1. empirical method (does not describe underlying physics)
  2. event-centric method (rainfall and runoff considered in isolated to other catchment conditions)
  3. To go beyond these limits must reimage catchment from physical principles
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15
Q

Water Storage

A
  1. Snow
    inflow = snowfall
    storage = snowpack
    outflow = snowmelt
  2. Interception
    inflow = precipitation
    storage = vegetation wetting
    outflow = stemflow, throughfall, evaporation
  3. water bodies
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16
Q

Linear Reservoirs Definition

A

Outflow is proportional to storage

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17
Q

Linear Reservoirs Eqn (not given)

A

Q = S/K (K is a constant)

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18
Q

Nash Reservoirs Definition

A

A linear reservoirs output becomes the input to another one in series

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19
Q

n meaning (Nash reservoirs)

A

number of reservoirs in series

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20
Q

k assumption (Nash reservoirs)

A

The same for all reservoirs

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21
Q

Effect of landuse on hydrographs

A

Water is accelerated through environment, hydrograph peak is higher and earlier

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22
Q

Evapotranspiration def

A

combination of evaporation and transpiration

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23
Q

Evaporation def

A

liquid water is converted to water vapour and removed from the evaporating surface

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24
Q

Transpiration def

A

Vaporisation of liquid water contained in plant tissues and vapour removal to the atmosphere

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25
Q

ET drivers

A
  1. heating by solar radiation
  2. heating by geothermal
  3. heating by re-radiation
  4. properties of vegetation/crop
  5. energy required to vaporise
  6. inhibition of vapour transport by an aerodynamic boundary layer
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26
Q

Different kinds of ET

A
  1. potential evapotranspiration
    - accounts for evaporation from water bodies or bare soil (penman eqn)
  2. Reference Evapotranspiration
    - accounts for two types of reference vegetation (tall or short crops) (penman monteith)
  3. Actual Evapotranspiration
    - accounts for all other vegetation and environmental factors
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27
Q

ETp

A

potential evapotranspiration [m/d]

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28
Q

ρw

A

water density [kg/m3]

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29
Q

λ

A

latent heat of vaporisation [MJ/kg]

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30
Q

Sn

A

Solar radiation [MJ/m2/d]

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31
Q

Ln

A

Re radiation [MJ/m2/d]

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32
Q

G

A

Soil heat flux [MJ/m2/d]

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33
Q

ρa

A

air density [kg/m3]

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34
Q

cp

A

specific heat of air [MJ/kg/C0]

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35
Q

es

A

saturated vapour pressure [kPa]

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36
Q

ea

A

actual vapour pressure [kPa]

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37
Q

ra

A

aerodynamic resistance [d/m]

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38
Q

Δ

A

vapour pressure gradient [kPa/C0]

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39
Q

γ

A

psychrometric constant [KPa/C0]

40
Q

What influences solar radiation

A

Latitude and earth-sun distance

41
Q

α

42
Q

as, bs

A

regression coefficients (0.25, 0.5)

43
Q

n

A

number of bright sunshine hours per day

44
Q

N

A

total number of sunshine hours per day

45
Q

Gsc

A

solar constant [MJ/m2/min]

46
Q

dr

A

inverse earth-sun relative distance

47
Q

Φ

A

latitude [rad]

48
Q

δ

A

solar declination [rad]

49
Q

ωs

A

sunset-hour angle

50
Q

J

A

Julian Day [1 to 365]

51
Q

σ

A

stefan-boltsman constant

52
Q

Rs/Rso

A

Relative solar radiation

53
Q

Ti+1

A

Soil temp NEXT month

54
Q

Ti-1

A

Soil temp PREVIOUS month

55
Q

Ts

A

water surface temperature

56
Q

u2

A

windspeed at 2m height

57
Q

rs

A

surface resistance by leaf stomata

58
Q

kc

A

crop coefficient

59
Q

ks

A

water stress factor

60
Q

Where to get evapotranspiration data from?

A
  1. local measuring
  2. remote sensing
  3. national/global data bases
61
Q

Why model evapotranspiration

A
  1. understand and predict soil moisture
  2. part of the water budget
62
Q

Infiltration def

A

surface to unsaturated soil

63
Q

Percolation def

A

soil to groundwater

64
Q

Capillary rise def

A

groundwater to soil (soil in saturated zone moves upwards)

65
Q

Interflow def

A

lateral flow in soil

66
Q

Soil-water/Matric potential def

A

Water drawn through narrow pore throats by capillary forces. Water’s affinity to adhere to pore surfaces

67
Q

Effects on soil-water

A
  1. small capillaries, water rises higher
  2. wet soil, higher suction
  3. sands more conductive than clays
68
Q

Process of infiltration

A
  1. soil column mostly dry
  2. it rains
  3. water seeps into ground through pores at top of soil
  4. infiltration initially rapid and slows overtime due to drag and reduces hydraulic gradient
69
Q

Green and Ampt Method

A
  1. Calculate soil parameters
  2. Find Δt and i(t+Δt)
  3. calculate infiltrability
  4. if i < infiltrability all infiltrates, if i < infiltrability only a fraction infiltrates
  5. calculate updated infiltration
70
Q

Antecedent Conditions

A

Effective saturation depends on the initial porosity filled with water. If it has rained recently initial porosity is greater so amount of saturation less and infiltrability less

71
Q

Alternative methods for infiltration

A

Phi-index
Horton

72
Q

What is land cover

A

the types of vegetation and built or natural features that cover the lands surface

73
Q

Land cover vs land use

A

Land use = the different ways that people use the land, land cover can be influences by land use

74
Q

Effect of land cover on infiltration

A

Impervious surfaces decrease infiltration

75
Q

Why model infiltration

A
  1. model flood severity
  2. manage recharge to groundwater
  3. avoid over irrigating
76
Q

Overland flow def

A

Flow of rainfall over land (first in sheets, then rills the larger gullies and channels)

77
Q

What is flow routing

A

Procedure to determine the time and magnitude of flow at a point upstream

traces flow through a hydrological system.

78
Q

Lumped flow routing

A

assumes flow rate and water level are a function of time

79
Q

hydrological limitations of overland flow

A
  • rapid changes to hydrology of catchment through land use
  • difficult to establish parameters
  • is desired to relate runoff to geographical features
  • desirable to model non-linear runoff characteristics
80
Q

Distributed flow routing

A

Flow rate velocity and depth vary with time and space

81
Q

Kinematic Waves

A

Gravity and friction forces are balanced

82
Q

kinematic vs dynamic waves

A

kinematic: mass and forces do not affect waves, in dynamic they do

83
Q

Kinematic flow

A

Steady (velocity constant with time) and uniform (velocity constant with distance)

84
Q

Tidal bores

A

standing waves travelling upstream

85
Q

What is K (Muskingham)

A

The time for a flood wave to travel the channel length

86
Q

How to choose X and K

A

plot storage vs XI+(I-X)Q and choose linear plot. K is gradient

86
Q

Error in Muskingum Method

A

numerical diffusion

87
Q

Muskingum Cunge advantages

A
  1. entire hydrograph obtained
  2. soln has less wave attentuation
88
Q

Muskingum Cunge disadvantages

A
  1. cannot handle downstream disturbances
  2. Not accurate at predicting hydrograph at downstream boundary
89
Q

Reservoir Routing

A

runoff enters storage which fills and allows water to exit through orifice flow and overflow

  • attenuation of peak flow
  • shifts peak
90
Q

A (orifice flow)

A

Orifice area

91
Q

Co

A

discharge coefficient

92
Q

hc

A

crest height

93
Q

h

A

water height

94
Q

Cs

A

discharge coefficient

95
Q

Storage indication method

A
  1. plot S on y axis and h on x axis
  2. plot Q on y axis and h on x axis
  3. plot storage indication on y axis and h on x axis
  4. plot Q on y axis and storage indication on x

5.1 Sj,Qj = 0, fine ij and ij+1
5.2 Calculate RHS
5.3 Calculate LHS
5.4 For given LHS find Q from plot (interpolate)
5.5 From LHS solve for S
5.6 repeat

practice (3 decks)

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