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GEO1020 > Hydrological Processes > Flashcards

Hydrological Processes Flashcards

1
Q

What are 3 measurements that can be made in the hydrological cycle?

A

Precipitation
Evaporation
River discharge (river gauging)

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2
Q

What does the lag time show on a hydrograph?

A

The time between rainfall and water entering the stream

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3
Q

What do individual storm hydrographs show?

A

How quickly rainwater moves from the hillslope to the stream channel

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4
Q

How do you find the rise time in a storm hydrograph?

A

Look at the difference between the peak storm flow and the first recorded rainfall

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5
Q

How do you find the lag time on a flood hydrograph?

A

The difference from the midpoint of the rainstorm and the peak storm flow

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6
Q

What is the time scale for studying and monitoring rivers?

A

Hours, days, months

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7
Q

What is the time scale for catchment dynamics?

A

Months, years, decades

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8
Q

What is the time scale for human impacts?

A

Years, decades, centuries, millennia

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9
Q

What is the time scale for natural variability?

A

Centuries onwards

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10
Q

What two things are monitored and studies related to rivers?

A

Environmental quality

Geomorphological processes

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11
Q

What are two key aspects of catchment dynamics?

A

Fluvial and biological responses

Catchment management

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12
Q

What are 5 human impacts?

A 
Acidification
Eutrophication
Desertification
Land-use 
River channel change
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13
Q

What are 3 examples of natural variability?

A

Climate change
Sea level change
Vegetation dynamics

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14
Q

What type of precipitation is easiest to measure?

A

Rain

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15
Q

Why is it difficult to measure snow?

A

Due to under catch

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16
Q

Is the weather radar integrated or instantaneous?

A

Integrated

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17
Q

What is the range of the weather radar?

A

Up to 200km

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18
Q

What is the weather radar range in the UK?

A

15 km

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19
Q

What is the weather radar range in Europe?

A

Over 100 km

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20
Q

What are 7 advantages of weather radars?

A

Area rainfall estimates over a wide area
Information in near-real time
Information for remote land areas and over adjacent seas
Location of frontal and convective (shower) precipitation
Monitoring movement and development of precipitation areas
Short-range forecasts made by extrapolation
Data can be assimilated into numerical weather prediction models

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21
Q

What are 3 disadvantages to weather radars?

A

Display does not show rainfall actually at the surface
Display also shows non-meteorological echoes
Estimates liable to error due to technical and meteorological causes

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22
Q

Explain stochastic variations in precipitation

A

Variability of rainfall in areas of low precipitation as longer records are needed
Timing and magnitude of storms is stochastic

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23
Q

Explain periodic variations of precipitation

A

Regular or cyclic variations
Daily or annual cycles such as convection
Land and sea breezes
Mediterranean winter rain

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24
Q

Explain secular variations of precipitation

A

Climate change

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25
Q

What 5 things does precipitation data show?

A 
Mean aerial input of rainfall from a series of point measurements
Storm patterns and movement
Storm recurrence
Probable maximum precipitation
Mean rainfall
26
Q

What is evaporation a major control on?

A

The Earth’s energy budget

27
Q

How much energy is used to evaporate water as opposed to heat it?

A

6x more energy is required to evaporate water than to heat if from 0-100 C

28
Q

Where is evaporation highest?

A

In areas with the highest rainfall

29
Q

Why is evaporation difficult to measure?

A

There is a loss of water at the surface

30
Q

What needs to be determined to measure evaporation?

A

The water vapour flux

31
Q

What is used to measure evaporation? (3)

A

Evaporation pans
Water vapour (lysimeter)
Weighing block

32
Q

What two things are used to determine discharge?

A

Channel cross-sectional area

Stream flow velocity

33
Q

What is the discharge equation?

A

Width x Depth x velocity

34
Q

What is width measured in?

A

m

35
Q

What is depth measured in?

A

m

36
Q

What is velocity measured in?

A

ms-1

37
Q

What are the units for discharge?

A

m3s-1`

38
Q

What do v-notch weirs allow?

A

Calculation of discharge using spillway equation

39
Q

What do propellors and impellors measure?

A

Velocity

40
Q

How often are velocity measurements made?

A

They are time averaged

41
Q

What are two advantages of measuring velocity with propellors and impellors?

A

They are robust and easy to use

42
Q

What are two disadvantages of measuring velocity with propellors and impellors?

A

They disrupt the flow they seek to measure and there are problems of near-bed measuring

43
Q

What is shear stress?

A

The rate of change of vertical velocity

44
Q

What is Faraday’s principle?

A

A conductor (water) moving through a magnetic field (produced by the sensor) generates a voltage

45
Q

What is voltage measured by in an electromagnetic current meter?

A

A pair of electrodes

46
Q

What are two advantages of electromagnetic current meters?

A

Possible to measure flow velocity in different dimensions

Good for use in streams with lots of vegetation and weeds

47
Q

What are ADVs?

A

Acoustic-Doppler Velocimeters

48
Q

Where can 3D turbulent velocities be found?

A

In rivers and flumes

49
Q

Where is the transmission of acoustic pulses from in ADVs?

A

From a transmitter at the probe head

50
Q

What transmission is sent from ADVs?

A

Acoustic pulses of 10MHz

51
Q

What happens to the acoustic pulse from an ADV?

A

It is reflected by air bubbles and suspended sediment within the flow

52
Q

How many receivers are in ADVs and what do they surround?

A

3 receivers surround a sampling volume of water

53
Q

What is the doppler shift from the ADV generated by?

A

It is generated by velocity differences between probe and scattering objects

54
Q

What is a disadvantage of ADVs?

A

Cannot measure close to river bed or water surface

55
Q

What are the velocities of ADVs?

A

Less than 2.5ms-1

56
Q

How does velocity vary?

A

Vary almost instantaneously and in several directions

57
Q

What are 3 main drawbacks of measuring river discharge?

A

Cannot gauge rivers all of the time
Need to find a simpler way of obtaining river discharge data over longer periods of time
Manual or automatic measurement of river level is much easier

58
Q

What relationship is needed?

A

A stage-discharge relationship

59
Q

What is the stage-discharge relationship derived from?

A

Multiple river gauging’s

60
Q

What conversion is required for stage-discharge relationship?

A

Conversion of river level (stage) to river discharge values

GEO1020 (16 decks)

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