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Water Resource Management > Surface Hyrology > Flashcards

Surface Hyrology Flashcards

1
Q

What does surface hydrology allow us to describe?

A

The fate of a water droplet once it hits the earth (identify –> Characterise –> quantify

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2
Q

How much water is used per person per day in the UK?

A

140 Litres/day

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3
Q

How much rainfall does London recieve in a year?

A

650mm/year

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4
Q

What can the water availability in London be described as?

A

Water scarce

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5
Q

What is the average volumetric flow rate of the Thame?

A

65 cubic meters a second

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6
Q

How much water is needed to produce 1 kg of beef

A

15,000L

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7
Q

What is the main assumption in hydrology for the global water cycle?

A

The total amount of water on Earth is constant

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8
Q

What is the error of a ‘good’ measurement in surface hydrology?

A

5-10%

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9
Q

What is the easiest flux to measure in the hydrological cycle? Why?

A

River Discharge

One-Dimensional problem, all the discharge flows in a distinct channel, dimensions of channel can be measured.

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10
Q

Why are fluxes such as precipitation and evaporation so difficult to measure?

A

They are two-dimensional problems, measuring at specific points is accurate and straight forward, however, spacial averages are much more challenging.

Groundwater and soils have similair limitations but can also become three-dimensional problems

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11
Q

What is the direct method for meauring the volumetric flow rate (m^3 s^{-1})?

A

Q = change in Volume/ Change in time = Delta V/ Delta T

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12
Q

What is the indirect method for meauring the volumetric flow rate (m^3 s^{-1})?

A

Integrate the velocity over the cross sectional area (multiply the average velocity by the cross sectional area Q =UA (Y1 fluids))

Lecture 1 slide 19/39

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13
Q

Name one method for caculating the mean flow rate in a river.

A

Mean-section method

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14
Q

What are some ways of measuring the velocity profile in a river?

A
  • Valeport propellor meter (density of data is very important)
  • Acoustic Doppler Velocity Profilers
  • Preasure transducer (automatic - multiple data points)
  • Staff gauge (easy to check at regular intervals)
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15
Q

What measurement does the water stage give you?

A

The water height

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16
Q

How are the water stage and the discharge related?

A

Stage-Discharge relationship

  • Often represented graphically
  • Formed using manual volumetric flow rate measurements at different water stages
  • result must be read off graph

Lecture 1 slide 24/39

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17
Q

What factors affect the stage discharge relationship?

A
  • Vegetation cycles
  • Ice cover
  • Erosion or sedimentation of channel
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18
Q

What civil engineering structures can allow a reliable stage discharge relationship to be defined?

A

Weirs and flumes

Weir: rise in the channel bed, creates a sub-critical upstream flow and super-critical downstream flow. Flow over the top of the Weir is critical - allows a reliable relationship to form

Flume: induces a critical flow by reducing the width of a section of the river (sometimes raises the bed). Reduces the risk of the sedimentation behind the control. Critical flow allows for reliable relationship

Lecture 1 slides 26–> 28 /39

19
Q

What are the main types of weir?

A
  • Sharp-crested
  • Broad-crested
  • Crump weirs
  • Special Weirs

Lecture 1 slides 26 &27/39

20
Q

Why does the South Tyne have a larger normalized river flow than the River Kennet?

A

The River Kennet has a permeable chalk layer, water flows through into the aquifer, and so the overall flow rate is lower

21
Q

What can be said about the dominant flow rate in a river? What does this say about the distribution of the flow rate when plotted on a histogram?

A

The low flow dominates.

This results in a positively skewed flowrate when plotted on a histogram

Lecture 1 slide 31/39

22
Q

How do you determine the start of the stormflow?

A

The local minima after the start of precipitation

23
Q

How do you find the time lag?

A

T_L = time@max flow - time @ max precip

24
Q

How do you find the end of the stormflow

A

time at end of the preciptiation + the time lag*N

N is usually == 4

25
Q

What is the ‘catchment area’?

A

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

26
Q

What is ‘evaporation’?

A

Loss of water to atmosphere from land/water surface

27
Q

What is the application of the conservation of mass in surface hyrdrology called?
What is it’s equation?

A

The catchment water balance
dS/dt = P(t) - E(t) - Q(t) - R(t) (1)

\DeltaS = S_t - S_0
= the integrtal between T and 0 of (1)

28
Q

What is the application of the conservation of energy in surface hyrdrology called?

A

The catchment energy balance - measure of how much energy has been used to evaporate the water

Lecture 2 slide 8/27

29
Q

What is the definition of humidity?

A

The amount of water vapor in a given point in the atmosphere

30
Q

What is the dewpoint (T_d)?

A

The temperature at which an ‘air-parcel’ becomes saturated.

31
Q

What is the definition of relative humidity?

A

The ratio between the vapour pressure and the saturation vapour pressure at the same temperature

r = (e_d/e_r)*100

32
Q

What is condensation?

A

When air masses are colled down to their dewpoint.

33
Q

What happens when air reaches its dewpoint?

A

Water starts to come out of the air as droplets

34
Q

What happens to the pressure gradient in the atmosphere, and what does this mean for precipitation?

A

As altitude increases, pressure decreases. Because of this gradient, air that is higher in the atmohsphere has a lower dewpoint

Lecture 2 slides 13&14/27

35
Q

What processes can cause atmospheric movements?

A
  • Convection
  • Orographic ascent
  • Shear ascent
  • Frontal ascent
36
Q

Describe convection

A

Localized heating at the surface produdcing buoyant air parcels

37
Q

Describe orographic ascent

A

Air being forced over an obstacle, such as wind passing over mountains

38
Q

Describe shear ascent

A

Differing wind velocities with height (wind shear) producing atmospheric turbulence, can induce vertical ascent

39
Q

Describe frontal escent

A

Air masses from different sources with different properties (warmer/ colder) meet, warmer air goes over the colder air, and leads to convective ascents

40
Q

Describe the saturation point of a soil

A

The maximum soil water content, all pores are filled

41
Q

Describe the field capcaity of a soil

A

the point at which the retention forces are greater than or equal to the gravitational forces

42
Q

Describe the wilting point of a soil

A

the maximum suction that plants can apply to extract water from the soil

43
Q

The soil moisture characteristic curve relates water content to what?

A

Matric Potential

Water Resource Management (1 decks)

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