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Hydrology Flashcards

(96 cards)

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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
ET drivers
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
26
Different kinds of ET
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
27
ETp
potential evapotranspiration [m/d]
28
ρw
water density [kg/m3]
29
λ
latent heat of vaporisation [MJ/kg]
30
Sn
Solar radiation [MJ/m2/d]
31
Ln
Re radiation [MJ/m2/d]
32
G
Soil heat flux [MJ/m2/d]
33
ρa
air density [kg/m3]
34
cp
specific heat of air [MJ/kg/C0]
35
es
saturated vapour pressure [kPa]
36
ea
actual vapour pressure [kPa]
37
ra
aerodynamic resistance [d/m]
38
Δ
vapour pressure gradient [kPa/C0]
39
γ
psychrometric constant [KPa/C0]
40
What influences solar radiation
Latitude and earth-sun distance
41
α
albedo
42
as, bs
regression coefficients (0.25, 0.5)
43
n
number of bright sunshine hours per day
44
N
total number of sunshine hours per day
45
Gsc
solar constant [MJ/m2/min]
46
dr
inverse earth-sun relative distance
47
Φ
latitude [rad]
48
δ
solar declination [rad]
49
ωs
sunset-hour angle
50
J
Julian Day [1 to 365]
51
σ
stefan-boltsman constant
52
Rs/Rso
Relative solar radiation
53
Ti+1
Soil temp NEXT month
54
Ti-1
Soil temp PREVIOUS month
55
Ts
water surface temperature
56
u2
windspeed at 2m height
57
rs
surface resistance by leaf stomata
58
kc
crop coefficient
59
ks
water stress factor
60
Where to get evapotranspiration data from?
1. local measuring 2. remote sensing 3. national/global data bases
61
Why model evapotranspiration
1. understand and predict soil moisture 2. part of the water budget
62
Infiltration def
surface to unsaturated soil
63
Percolation def
soil to groundwater
64
Capillary rise def
groundwater to soil (soil in saturated zone moves upwards)
65
Interflow def
lateral flow in soil
66
Soil-water/Matric potential def
Water drawn through narrow pore throats by capillary forces. Water's affinity to adhere to pore surfaces
67
Effects on soil-water
1. small capillaries, water rises higher 2. wet soil, higher suction 3. sands more conductive than clays
68
Process of infiltration
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
Green and Ampt Method
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
Antecedent Conditions
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
Alternative methods for infiltration
Phi-index Horton
72
What is land cover
the types of vegetation and built or natural features that cover the lands surface
73
Land cover vs land use
Land use = the different ways that people use the land, land cover can be influences by land use
74
Effect of land cover on infiltration
Impervious surfaces decrease infiltration
75
Why model infiltration
1. model flood severity 2. manage recharge to groundwater 3. avoid over irrigating
76
Overland flow def
Flow of rainfall over land (first in sheets, then rills the larger gullies and channels)
77
What is flow routing
Procedure to determine the time and magnitude of flow at a point upstream traces flow through a hydrological system.
78
Lumped flow routing
assumes flow rate and water level are a function of time
79
hydrological limitations of overland flow
- 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
Distributed flow routing
Flow rate velocity and depth vary with time and space
81
Kinematic Waves
Gravity and friction forces are balanced
82
kinematic vs dynamic waves
kinematic: mass and forces do not affect waves, in dynamic they do
83
Kinematic flow
Steady (velocity constant with time) and uniform (velocity constant with distance)
84
Tidal bores
standing waves travelling upstream
85
What is K (Muskingham)
The time for a flood wave to travel the channel length
86
How to choose X and K
plot storage vs XI+(I-X)Q and choose linear plot. K is gradient
86
Error in Muskingum Method
numerical diffusion
87
Muskingum Cunge advantages
1. entire hydrograph obtained 2. soln has less wave attentuation
88
Muskingum Cunge disadvantages
1. cannot handle downstream disturbances 2. Not accurate at predicting hydrograph at downstream boundary
89
Reservoir Routing
runoff enters storage which fills and allows water to exit through orifice flow and overflow - attenuation of peak flow - shifts peak
90
A (orifice flow)
Orifice area
91
Co
discharge coefficient
92
hc
crest height
93
h
water height
94
Cs
discharge coefficient
95
Storage indication method
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

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