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Enveng 333 > Hydrological Cycle > Flashcards

Hydrological Cycle Flashcards

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1
Q

Name the 3 main mechanisms of precipitation?

A

Frontal, Convective, Orthographic

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2
Q

Explain “Frontal” precipitation

A

Cold air pushes warm moist air up

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3
Q

Explain “Convective” precipitation

A

Warm moist air rises due to heated ground surface (occurs in summer from solar heating of the ground)

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4
Q

Explain “orthographic” precipitation

A

Moist air is pushed up due to topography of the land

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5
Q

Define precipitation

A

Any product of the condensation of water vapour that falls due to gravity (rain and snow)

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6
Q

Define infiltration

A

The portion of rainfall that enters the soil

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7
Q

Define surface runoff

A

The portion of precipitation that flows on the land surface

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8
Q

Define evaporation

A

Process of the hydrological cycle that causes a phase change of water from liquid to vapor, final product of process is vapour in atmosphere

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9
Q

Define Transpiration

A

The evaporation from plants through the stomata openings

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10
Q

True or false

We try to mimic previous Hydrology

A

True

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11
Q

Define watershed (catchment)

A

Area of land that collects water and drains to a single outlet

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12
Q

What are the advantages of indigenous knowledge

A

Indigenous knowledge has a holistic of community and environment

Source for adapting to climate change

Oberservation driven and passed on from word of mouth

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13
Q

List three ways of rainfall estimation/measurement, also say whether they are direct or indirect

A

Rainfall Gauges (direct)

Radar (indirect)

Satellite (indirect)

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14
Q

Problems with rainfall gauges

A 
Accessibility
Require matenance by skilled personnel
Need to be powered (in some cases) 
Vandalism 
Exposure of gauge may effect accuracy
Redundancy
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15
Q

Name the 4 main methods for estimating mean areal rainfall

A

Arithmetic method
Thiessen polygons
Isohyetal
Hypsometric method

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16
Q

Explain the arithmetic method for rainfall estimation and when this method should be used

A

You take the average of the measured rainfall values in the catchment area.

Use when:

  • topography is flat
  • the gauging stations are distributed evenly over catchment
  • density of gauging stations is adequate
  • not too much variability of rainfall
17
Q

Explain the Thiessen polygon method

A

Divide catchment into set of polygons (one for each station)

The polygons represent the area of catchment nearest to station

Polygons are made by drawing lines joining stations then off those lines drawing perpidicular bisectors

18
Q

List advantages of Thiessen polygon method

A

Simple

Stations outside catchments can be included

19
Q

List the disadvantages of Thiessen polygon method

A

Not suitable for mountainous area (doesn’t take into account orthographic effects)

Have to draw new set of polygons if rainfall gauges are added or removed

20
Q

Explain the Isohyetal Method

A

You draw an Isohyetal map, this map is made up of Isohyets which are contour lines that show equal rainfall depths. The mean areal rainfall is calculated by using the waited average rainfall depths between isohyets. NOTE I.E. You find the average of the rainfall depths over succsessive isohyets and multiply by area between isohyets. Sum of these is the mean depth

21
Q

Disadvantages if Isohyetal method

A

Drawing of Isohyetal map can be tedious and time consuming. The resulting map is subjective so final results may vary.

22
Q

What are the pros/cons of the hypsometric method

A

Pros takes into account orthographic effects

Cons requires a topographical map

23
Q

What factors affect infiltration

A

Slope (large slopes less infiltration)

Land cover (vegetation causes higher infiltration)

Soil type (increased void space causes higher infiltration)

Soil temperature (frozen soils become dense and less permeable)

Initial moisture content(if the MC is high infiltration rate is lower

Depth of ground water table (linked to moisture content)

24
Q

What are river flow measurements needed for

A

Design and water management of dams

Flood forecasting and control

Irrigation

Energy generation (hydro)

Management of water quality in rivers

Scientific research

25
Q

Impacts of climate change on hydrological cycle

A

Change in average surface temperature (can change evaporation rates)
Change in average precipitation
Change in average sea level

26
Q

Define remote sensing

A

Indirect rainfall measurement, radars/satallites

27
Q

Uses of rainfall estimation

A

Riverflow forecastinf

Crop forecastinf

Famine warning system

Malaria warning system

28
Q

Principle if estimation by radar

A

Radar emits electromagnetic energy which is partially scattered, absorbed and reflected when it hits the clouds
Some of the reflected energy returns to transmitter
The amount of energy reflected can be used to estimate rainfall

29
Q

Indirect river gauging methods

A

Empirical rating curves (natural controls)

Theoretical rating curves (artificial controls such as weirs and flumes)

30
Q

Direct gauging methods

A

Velocity - Area method

Dilution method

31
Q

List the fundamental principles of unit hydrograph theory

A

Proportionality
Super position
Time invariance

32
Q

Explain proportionality in terms of the Unit Hydrograph Principles

A

Two different effective rainfall intensities, but of equal duration produce hydrographs of storm runoff, the ordinates of which, at any given time are in the same proportion to each other as the effective rainfall intentisies.

33
Q

What is the basic assumption of CN method

A

Runoff occurs immediately after initial abstraction volume is satisfied (once all soil voids are filled)

34
Q

What are the principle assumptions made in frequency analysis

A

The sample is assumed to be a random samplr

The variation of the magnitude of the event can be described by a probability distribution

The relationship between the magnitude of the event and its return period do not vary with time

Enveng 333 (1 decks)

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