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Civ Eng Y2 > Environmental > Flashcards

Environmental Flashcards

1
Q

The water cycle?

A

Atmosphere ->
Precipitation & snow ->
Surface runoff, infiltration ->
Ground water flow -> ocean
Evaporation

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2
Q

River discharge?

A

The flux of water through the river cross section of a point along a river
(L^3 T^-1) and (LT^-1) for runoff)

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3
Q

Hydrograph?

A

Plot of discharge over time

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4
Q

Q= vA (river)

A

River flux = average velocity * area of cross section

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5
Q

River velocity meters? (3)

A
  • valeport propeller meters
  • acoustic Doppler velocity profilers (ADVP) larger rivers
  • measure river height (stage) and use stage discharge graph to predict discharge
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6
Q

Weir?

A

A rise in a channel bed which creates sub- critical upstream flow and super critical downstream flow with the critical section at the weir

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7
Q

Where can you derive a reliable theoretical stage- discharge relationship?

A

Weirs

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8
Q

How do you predict an end to a storm?

A

Identify the start of the stormflow by finding the inflexion point in the hydrograph. This often coincides with the start of the precipitation event and the start of the stormflow.

Then times the lag time (peak storm flow- peak precipitation) * 4(N) and then add this to the end of precipitation.

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9
Q

How can you get base flow from a hydrograph with stormflow?

A

You can remove stormflow by using a straight line

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10
Q

Catchment area?

A

The drainage area contributing to flow at a point on a river

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11
Q

Precipitation? (2/4)

A
  • rainfall
  • snow
  • sleet
  • hail
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12
Q

Hyetograph?

A

Plot of rainfall over time

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13
Q

ΔS = P - E - Q - R

A

Change in internal catchment storage = precipitation - evaporation - river runoff - groundwater recharge

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14
Q

Humidity?

A

The amount of water vapour in the atmosphere at a given point

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15
Q

Absolute humidity (ρw) vapour pressure (e) [mb]?

A

The mass of water vapour per unit volume of air [g/ m^3]

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16
Q

Dew point (Td)

A

The point where air parcels have cooled down through condensation enough to become saturated

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17
Q

r= (ed/ ea) * 100

A

relative humidity = parcel’s vapour pressure / the saturation vapour pressure at the same temperature * 100

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18
Q

What happens to the amount of water in air as temperature increases?

A

It increases too

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19
Q

What impact does the pressure gradient have as air makes its way up the atmosphere?

A

It will expand and cool potentially generating precipitation

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20
Q

What are four mechanisms that make vertical air movement?

A
  • convection
  • orographic ascent
  • shear ascent
  • frontal ascent
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21
Q

Convection?

A

Localised heating at surface produces buoyant air parcels

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22
Q

Orographic ascent?

A

Air forced to flow over an obstacle

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23
Q

Shear ascent?

A

Differing wind velocities with height induce atmospheric turbulence in all directions, including vertical ascent

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24
Q

Frontal ascent?

A

The meeting of air masses of different origins and properties results in the cooler ( more dense) air undercutting the warmer (less dense) air. This leading to widespread ascent, which, in turn, can also give rise to localised connective ascent

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25
Three ways of measuring precipitation?
- manual rain gauges - automatic rain gauges - tipping bucket rain gauges
26
Three sources of errors for rain gauges?
- deflection of air by rain gauge ( horizontal flow) - upward deflection over gauge (turbulent flow) - downward deflection of air over gauge (turbulent flow)
27
How does a remote sensing weather radar work?
A narrow beam of microwave electromagnetic energy undergoes Rayleigh scattering when the beam encounters water droplets. A certain proportion of radiation is back scattered and can be measured
28
Spatial variability of precipitation*
Precipitation is often measured at a point scale. To calculate and analyse the water balance of a catchment, we need the flux over the basin area A. Therefore, it is often necessary to interpolate precipitation to obtain a spatial average. Many methods exist. But note that: - the network density affects spatial accuracy - the required distribution of stations is related to data requirements and physical features - the quality of interpolation depends on rainfall type, typography, time scale
29
Isohyets?
Lines of equal precipitation across the catchment drawn by a skilled analyst
30
λE=Rn +C +V + G - Ps
λ= latent heat of vaporisation of water E= evaporation Rn= net radiation C= sensible heat transfer V= change in energy storage G= energy exchange with the ground Ps= energy consumed by photosynthesis
31
β= C/ λE
Bowen’s ratio = sensible heat transfer/ latent heat of vaporisation of water * evaporation
32
Factors of evaporation?
Meteorological: - solar radiation - relative humidity - wind speed Physical: - salinity (sea water evaporates less than fresh water) - water depth - size of the water surface
33
Water cycle in plants?
Precipitation is collected -> - Interception loss -stemflow - through full
34
Factors affecting interception loss?
- interception storage capacity of the vegetation cover - type and morphology of the vegetation cover - velocity of evaporation - duration and intensity of the precipitation event - precipitation event frequency
35
Evapotranspitation (Et)?
The combined process of direct evaporation and transpiration as plants enhance evaporation through root water uptake and transpiration
36
Factors of transpiration?
- number, size and distribution of stomata - the thickness and permeability of the epidermis - the area of internal surfaces exposed to intercellular spaces - the arrangement of the vascular tissue - solar radiation, stomata close at night, which reduces transpiration
37
Et0 = (0.408Δ(Rn-G) + γ(900/(T+273)) u2 (es-ea) ——————————————————— Δ+ γ(1+0.34u2)
Et0 = initial evapotranspiration Rn= net radiation at the crop surface G= soil heat flux density T= mean daily air temperature u2= wind speed at 2m height es= saturation vapour ea= actual vapour pressure Δ= slope vapour pressure curve γ= psychrometric constant
38
Ep= Kc Et0
Ep= potential ET Kc= crop or vegetation coefficient Et0 = reference ET
39
Et = Kc Ks Et0
Et= actual ET Kc= crop or vegetation coefficient Ks = water stress coefficient Et0 = reference ET
40
How is stem flow measured?
Using simple setups of water collection combined with a water flow meter
41
How is through fall measured?
With rain gauges installed under the canopy. Because of the spatial heterogeneity of the canopy, several rain gauges are required to get a representative sample
42
How can Et be measured?
With lysimeter experiements. A lysimeter contains a known volume of soil including a vegetation layer. The total mass of the soil volume is frequently weighed. By closing the water balance, the evaportranspiration flux can be obtained. This needs careful monitoring of precipitation and other changes in mass. Given the complexity of lysimeter experiments, set values are typically calculated using hydrometeorological measurements combined with empirical crop characteristics.
43
Unsaturated zone?
The portion of the subsurface above the groundwater table. The soil and rock in this zone contains air as well as water in its pores.
44
3 outgoing fluxes + 1 property of the unsaturated zone?
- overland flow - recharge - evaporation - has water storage capacity
45
How is the unsaturated zone created?
The unsaturated zone soil is formed by disintegration and decomposition of rocks by physical and chemical processes, and by the activity and accumulation of the residues of numerous plants and animals. It is a complex mixture of solids both rocks and organic materials, liquid and gases
46
ρs = Ms/ Vs
Density of solids = mass of solids/ volume of solids
47
ρB = Ms/ VT
Dry bulk density = mass of solids/ total volume
48
ρT = Ms+ ML/ VT
Total bulk density = mass of solids + mass of liquids / total volume
49
ε = VL+ VG / VT
Porosity = volume of liquids and gas / total volume
50
e =VL + VG / VS
Void ratio = volume of liquids and gases / volume of solids
51
ε = e/ (1+e)
Porosity = void ratio/ (1+ void ratio)
52
θ= VL/ VT
Volumetric moisture content = volume of liquids/ total volume
53
θG = ML/ MS
Gravimetric moisture content = liquid mass/ solid mass
54
Fluid potential
Mechanical energy per unit mass of fluid
55
Capillarity force?
A result of the surface tension at the interface between the soil air, soil water and soilids
56
Absorption force?
Occurs on surfaces of soil particles due to electrostatic forces in which the polar water molecules are attached to the charged faces of the solids
57
Osmosis force?
Results from the presence of solutes in the water
58
Soil water potential?
The potential energy of soil water relative to that of water in a standard reference state. Thus is determined by capillarity, absorption, osmosis and gravity
59
h = 2*γ*cosθ / ρgr
h= height of water from capillary tube water top to water table γ = the liquid air surface tension θ= the contact angle ρ = density of the liquid g= gravimetric constant r = radius of the tube
60
Explain the relationship between pore sizes and capillary forces?
Soil pore spaces act like capillary tubes. Therefore, the soil will retain water against the force of gravity. The effect decreases rapidly with increasing radius of the tube, and therefore water will be retained stronger in small pores than in longer pores.
61
Matric potential?
The potential energy of water related to the capillary retention (matric suction)
62
Ψ = Φ/ ρg
Water pressure head= matric potential / density * gravimetric constant (9.81)
63
What will the pressure head associated with capillarity always be?
Negative compared to the reference position outside the soil
64
Water retention curve?
Gives the empirical relation between ψ (pore pressure head/ matric suction). The higher the volumetric water content the lower the matric suction
65
What happens when the matric suction = 0
The soil is completely saturated
66
What happens when force is applied to saturated soil?
Air will replace the water gradually. Water with lowest tension (large pores) will be released first
67
Saturation point?
The maximum soil water content. All pores are filled
68
Field capacity?
Occurs when excess water has drained away. Beyond this point, the soil will not drain further because retention forces exceed the gravitational force
69
Wilting point?
Maximum suction that plants can apply to extract water from the soil
70
h= ψ + z
Hydraulic head = pore water pressure head (matric suction) + gravitational head
71
v= -k(θ) Δh
v= velocity K(θ) = hydraulic conductivity Δh= total hydraulic head gradient in 3 dimensions
72
Saturated conductivity Ks
The hydraulic conductivity in saturated conditions
73
Infiltration capacity?
The saturated conductivity at the soil surface
74
Explain the relationship of hydraulic conductivity (K) and matric potential (ψ)
Water moves quicker through larger pores than though smaller pores. When a suction is applied, the larger pores will empty first, forcing water to flow through the smaller pores. The shape of the curve depends on the pore distribution in a type of soil. Sandy soils tend to have larger pores than clayey soil and will therefore have higher conductivity.
75
How do forces work in the unsaturated zone?
Flow in the unsaturated zone is predominantly vertical under the influence of gravity. It will recharge the saturated zone, causing the water table to move. This may cause pressure gradients which will force water to flow horizontally.
76
What acts as the storm flow and base flow in the unsaturated soil?
Storm flow is the runoff/ ground water flow. Base flow is the ground water recharge
77
TDR (Time domain reflectrometry)?
Used to measure soil moisture. The dielectric constant of soil is strongly dependent on its water content. The dialectic constant is determined by the travel time of an electromagnetic wave that propagates through two or more parallel metal rods in the soil
78
SMD?
Soil moisture deficit = Σ Vg/VT
79
AWC?
Actual water content = ΣVL/ VT
80
Potential evapotranspiration? Ep
Occurs when enough water is available
81
The actual evapotranspiration? Et/ Εa
May be lower due to water stress than potential evapotranspiration
82
Reference evapotranspiration Et0
The evapotranspiration of a sufficiently watered reference crop, typically grass
83
What two thinks is Et limited by?
Available water and available energy

Civ Eng Y2 (5 decks)

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