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CIV E 321 > Midterm Prep > Flashcards

Midterm Prep Flashcards

1
Q

What are the Four Basic Parts of the Hydrologic Cycle?

A
  1. Precipitation - Moisture falling from the atmosphere to earth
  2. Evaporation (or Evapotranspiration) - Return of water vapour to the atmosphere
  3. Storage - Water that remains in pools or soaks through the ground and infiltrates groundwater
  4. Runoff (or Overflow Land) - Water that hits the earth and flows over land and into channels
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2
Q

What are the water balance equations?

A

Amount In - Amount Out = Change in Storage
- When applied to the mass of water moving through various portions of the hydrologic cycle

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3
Q

What is a watershed?

A

The area that topographically appears to contribute all the water that passes through a specific cross-section of a stream (the outlet).

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4
Q

Describe both incoming and outgoing energy.

A

Incoming energy is shortwave radiation from the sun and longwave radiation from the absorption and re-emission of energy by atmospheric gases.
Outgoing energy is latent heat (from water phase change) and sensible heat (from energy transfer between land surfaces and atmosphere [Causes temperature change])

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5
Q

What are the three main types of rainfall?

A

Frontal, Orographic, and Connective (based on corresponding air-mass lifting)

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6
Q

Rank the 4 main types of precipitation based on diameter.

A

Drizzle < Rain < Snow < Hail

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7
Q

How can precipitation be measured?

A
  1. Directly through a rain gauge.
  2. indirectly using remote sensing.
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8
Q

What are the 5 methods we use to quantitatively describe rainfall?

A
  1. Duration - Time Elapsed
  2. Depth
  3. Intensity - Ratio of depth to duration (mm/hr)
  4. Frequency - Average time elapsed between rainfall events
  5. Return Period - Reciprocal of frequency
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9
Q

What is a hyetograph?

A

A histogram of rainfall depth or intensity with time.
- Discrete form of temporal rainfall distribution

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10
Q

What is a cumulative mass curve?

A

A cumulative rainfall depth with time.
- Continuous form of temporal rainfall distribution

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11
Q

What is an isohyet and what is it used for?

A
  • A contour line showing the loci of equal rainfall depth.
  • Used to depict the spatial variation of rainfall
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12
Q

Describe the uniform weight method for measuring average precipitation over an area.

A

Take the average rainfall of the gages and divide them by the total number of gages.

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13
Q

Describe the Thiessen Polygon method for measuring average precipitation over an area.

A
  1. Join gages with straight lines to form triangles.
  2. Draw perpendicular bisectors to the sides of these triangles to enclose each gage within a polygon (a Thiessen Polygon!), forming an area of influence.
  3. Calculate Pavg by weighing each gage’s rainfall depth in proportion to its area of influence.
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14
Q

Describe the Isohyetal method for measuring average precipitation over an area.

A
  1. Find the average rainfall between each pair of contours.
  2. Multiple it by the area between the contours.
  3. Sum Step 2.
  4. Divide Step 3. by the total area.
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15
Q

What does IDF stand for in “IDF Curve”?

A

Intensity-Duration-Frequency

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16
Q

What can we apply statistical methods to the long series of rainfall data for?

A

The design of:
- Infrastructure (Storm drainage systems, Bridges, Dams/Reservoirs)
- Hydrologic Structures
- Flood Planning

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17
Q

Define time of concentration.

A

The time needed for water to flow from the remotest part of a watershed to the outlet

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18
Q

Define rainfall excess.

A

The rainfall that is neither retained on the ground surface nor retained in the soil.
- The amount of rainfall that runs off the watershed surface to become streamflow

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19
Q

What is the main disadvantage of IDF curves and what is the result?

A

IDF curves assume a storm of constant intensity for a given duration, but i is NOT constant, especially for longer storms. The underestimated peak intensity results in an underestimated peak flow.

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20
Q

What is a synthetic storm hyetograph?

A

A dimensionless temporal rain distribution that is used to convert a storm depth into a hyetograph.

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21
Q

Define evaporation.

A

The process by which water is transformed from the liquid phase to the vapour phase.

22
Q

What are the top two most important qualities in regional water budgets?

A
  1. Rainfall
  2. Evaporation and evapotranspiration
23
Q

What is a Class-A pan and what complications are associated?

A

A way to measure evaporation.
Complications:
1. Less heat-storage capacity - heats quicker
2. Pan sides can be exposes to sunlight and air (larger temperature variation).
3. Pans lack surface and groundwater inputs/outputs.

24
Q

What are some approaches to estimating evaporation?

A
  1. Water budget methods (P-(E+Q) = (delta)s)
  2. Energy budget methods
    (short-wave + long-wave radiation = sensible + Latent)
  3. Mass transfer methods ( saturation vapour pressure difference)
  4. Combination methods
25
Q

Define transpiration.

A

The process by which water moves through plants and evaporates through leaf stoma.

26
Q

Define potential ET.

A

The maximum amount of water that could evaporate from the soil and be transpired by plants given unlimited water supply.

27
Q

Define reference crop ET.

A

The ET from a large area completely and uniformly covered with a specific reference crop and with unlimited water supply.

28
Q

Define actual ET and describe how it is measured.

A
  • The amount of water that is actually removed from a land surface due to the actual soil, land, ground-cover, and water availability.
  • Lysimeters consist of an isolated contained with a column of soil and vegetation growing on it. Water balance is monitored by measuring the inputs, outputs and change in storage of water within the control volume.
29
Q

Define infiltration.

A

The process by which water arriving at the soil surface as rain and snowmelt enters the soil.

30
Q

Describe how the abstracted water moves once below the surface.

A
  • Laterally, as interflow, into streams, lakes and rivers.
  • Vertically, as percolation, into aquifers.
31
Q

What are infiltration rates affected by?

A
  • Land surface conditions
  • Vegetation cover
  • Storm characteristics (intensity, depth, duration)
  • Soil properties
  • Water temperature and quality (including chemical constituents)
32
Q

Describe soil.

A
  • A matrix of individual soil grains
  • Interconnected pore spaces (filled with water or air) in between soil particles
  • Grains, water and air make soil a three-phase system
33
Q

Define percentage finer.

A

The weight proportion of soil particles in a sample that are smaller/finer than a specific size.

34
Q

Describe soil texture.

A
  • Used to characterize the grain-size distribution
  • After removing particles larger than sand, soil texture is defined based on proportions (by weight) of clay, silt and sand
35
Q

Describe loam.

A

A popular type of soil among gardeners and farmers.
- Contains a good mix of all 3 soil types as well as humus
- Retains moisture and nutrients making it more suitable for farming

36
Q

Define capillary rise.

A

Water moves from the saturated zone upward to the unsaturated zone through surface tension.

37
Q

Define field capacity.

A

The ideal water content of the soil for plant growth.
- The upper limit of water availability for most plants as it provides enough moisture without causing water logging.

38
Q

Define permanent wilting point.

A

The soil moisture level at which plants can no longer extract water from the soil, leading to wilting.
- Represents the lower limit of available for plants.

39
Q

What are the limitations of Horton’s equation?

A
  1. It assumes continuous ponding conditions.
  2. Infiltration capacity should not reduce with time, but should in proportion to cumulative infiltration.
40
Q

What two assumptions are unique to Horton’s Law?

A
  1. Empirical exponential decay of fp over time
  2. Experimental, accepted values for assumed fo and fc
41
Q

What are the 4 assumptions for infiltration laws?

A
  1. Soil is homogenous and isotropic.
  2. Uniform soil moisture content.
  3. Ponding water on the ground surface
    • Unlimited water supply
    • i&raquo_space; fp
  4. Water flows in a one-dimensional vertical flow (only!)
42
Q

What three assumptions are unique to Darcy’s Law?

A
  1. Sharp wetting front.
  2. Soil behind wetting front is saturated.
  3. Suction head is constant at the wetting front.
43
Q

Define saturated hydraulic conductivity (Ks).

A

A measure of the soil’s ability to transmit water when it is fully saturated.
- Lower for finer-textured soils due to their small pore spaces and greater resistance to water flow.

44
Q

Define hydraulic head (H).

A

A measure of the energy in the body of water.

45
Q

Define suction head (ψ).

A

A measure of the force that soil exerts to absorb and retain water, drawing it into the pore spaces of the soil column.
- Driver is the surface tension of soil particles
- Finer-textured soils have a higher value because they can retain water tightly.

46
Q

Define runoff.

A

All the water flowing on the surface of the Earth, either by overland flow or by channel flow in creeks, streams, rivers, or gullies.

47
Q

What are three sources that runoff consists of?

A
  1. Overland Flow - product of direct rainfall
  2. Interflow - occurs in unsaturated zone
  3. Groundwater Flow - occurs is saturated zone
48
Q

Define the three stream types.

A
  1. Perennial: Always contain flow, typically in humid regions
  2. Ephemeral: Have flow only in response to storms
  3. Intermittent: Sometimes like perennial, sometimes like ephemeral
49
Q

What is a hydrograph?

A

A graphical representation of the flow rate of water (or discharge) in a stream or river over time at a specific point.

50
Q

What is a unit hydrograph?

A

A hypothetical hydrograph of the direct runoff resulting from one unit of rainfall excess.

51
Q

What is the area under a unit hydrograph?

A

Volume of the direct runoff

52
Q

What is an S-hydrograph?

A

The response to a storm of infinite duration and intensity.
- Converges to a constant value since the ordinates of the UH are only non-zero for a finite interval of time

CIV E 321 (2 decks)

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