Environmental

Question 1

The water cycle?

Answer 1

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

Question 2

River discharge?

Answer 2

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

Question 3

Hydrograph?

Answer 3

Plot of discharge over time

Question 4

Q= vA (river)

Answer 4

River flux = average velocity * area of cross section

Question 5

River velocity meters? (3)

Answer 5

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

Question 6

Weir?

Answer 6

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

Question 7

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

Answer 7

Weirs

Question 8

How do you predict an end to a storm?

Answer 8

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.

Question 9

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

Answer 9

You can remove stormflow by using a straight line

Question 10

Catchment area?

Answer 10

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

Question 11

Precipitation? (2/4)

Answer 11

• rainfall
• snow
• sleet
• hail

Question 12

Hyetograph?

Answer 12

Plot of rainfall over time

Question 13

ΔS = P - E - Q - R

Answer 13

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

Question 14

Humidity?

Answer 14

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

Question 15

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

Answer 15

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

Question 16

Dew point (Td)

Answer 16

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

Question 17

r= (ed/ ea) * 100

Answer 17

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

Question 18

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

Answer 18

It increases too

Question 19

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

Answer 19

It will expand and cool potentially generating precipitation

Question 20

What are four mechanisms that make vertical air movement?

Answer 20

• convection
• orographic ascent
• shear ascent
• frontal ascent

Question 21

Convection?

Answer 21

Localised heating at surface produces buoyant air parcels

Question 22

Orographic ascent?

Answer 22

Air forced to flow over an obstacle

Question 23

Shear ascent?

Answer 23

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

Question 24

Frontal ascent?

Answer 24

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

Question 25

Three ways of measuring precipitation?

Answer 25

• manual rain gauges
• automatic rain gauges
• tipping bucket rain gauges

Question 26

Three sources of errors for rain gauges?

Answer 26

• deflection of air by rain gauge ( horizontal flow)
• upward deflection over gauge (turbulent flow)
• downward deflection of air over gauge (turbulent flow)

Question 27

How does a remote sensing weather radar work?

Answer 27

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

Question 28

Spatial variability of precipitation*

Answer 28

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

Question 29

Isohyets?

Answer 29

Lines of equal precipitation across the catchment drawn by a skilled analyst

Question 30

λE=Rn +C +V + G - Ps

Answer 30

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

Question 31

β= C/ λE

Answer 31

Bowen’s ratio = sensible heat transfer/ latent heat of vaporisation of water * evaporation

Question 32

Factors of evaporation?

Answer 32

Meteorological:
- solar radiation
- relative humidity
- wind speed

Physical:
- salinity (sea water evaporates less than fresh water)
- water depth
- size of the water surface

Question 33

Water cycle in plants?

Answer 33

Precipitation is collected
->
- Interception loss
-stemflow
- through full

Question 34

Factors affecting interception loss?

Answer 34

• 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

Question 35

Evapotranspitation (Et)?

Answer 35

The combined process of direct evaporation and transpiration as plants enhance evaporation through root water uptake and transpiration

Question 36

Factors of transpiration?

Answer 36

• 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

Question 37

Et0 =
(0.408Δ(Rn-G) + γ(900/(T+273)) u2 (es-ea)
———————————————————
Δ+ γ(1+0.34u2)

Answer 37

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

Question 38

Ep= Kc Et0

Answer 38

Ep= potential ET
Kc= crop or vegetation coefficient
Et0 = reference ET

Question 39

Et = Kc Ks Et0

Answer 39

Et= actual ET
Kc= crop or vegetation coefficient
Ks = water stress coefficient
Et0 = reference ET

Question 40

How is stem flow measured?

Answer 40

Using simple setups of water collection combined with a water flow meter

Question 41

How is through fall measured?

Answer 41

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

Question 42

How can Et be measured?

Answer 42

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.