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Hydrogeology > Lesson 4: Principles of Groundwater flow > Flashcards

Lesson 4: Principles of Groundwater flow Flashcards

1
Q

Groundwater possesses energy in 3 forms, what are they?

A

mechanical, thermal, and chemical forms

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2
Q

There are three (3) external forces acting on groundwater, what are they?

A

gravity, external pressure, and molecular attraction.

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3
Q

When water in ground is flowing through a porous medium, there are 3 forces resisting the fluid movement, what are they?

A
  • shear stresses
  • normal stress acting
  • internal molecular attraction of the fluid itself
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4
Q

device used to measure liquid pressure in a system by measuring the height to which a column of the liquid rises against gravity

A

Piezometer

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5
Q

a device which measures the pressure of groundwater.

A

piezometer

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6
Q

pressure of groundwater is called

A

piezometric head of groundwater

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7
Q

describe the velocity of groundwater flowing in
porous medium under natural hydraulic
gradient.

A

very low

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8
Q

average hydraulic gradient of streams during floods

A

10 m/s

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9
Q

The total hydraulic head is given by the formula ?

A

h = z + hp

the sum of the elevation head and the pressure head.

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10
Q

flow direction points to what value of head

A

to lower hydraulic head

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11
Q

what causes density variation to the hydraulic head?

A

salinity

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12
Q

water level in well filled with water coming from a point in an aquifer and which is just enough to balance the pressure in the aquifer at that point

A

Point-water head

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13
Q

the height of a column of fresh water in a well that is just sufficient to balance the pressure in the aquifer at that point

A

Fresh-water head

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14
Q

how to calculate for fresh water head

A

add the elevation head and fresh water pressure head

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15
Q

Total mechanical energy per unit mass

A

Force Potential

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16
Q

Force Potential is sum of what?

A

sum of the kinetic energy, elevation energy, and pressure.

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17
Q

driving impetus behind groundwater flow and is equal to the product of hydraulic head and the acceleration due to gravity.

A

Force potential (Φ)

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18
Q

Force potential (Φ) formula

A

Φ = gh

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19
Q

force potential is equal to what

A

Total mechanical energy

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20
Q

Hydraulic head _______ in the direction of the flow.

A

decreases

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21
Q

As groundwater moves, it encounters ________ between the fluid and the porous media

A

frictional resistance

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22
Q

Groundwater is _____ slightly as it flows and ______ energy is converted to _______ energy.

A

warmed;
mechanical;
thermal

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23
Q

when groundwater moves, is the change in temp measurable?

A

not under most circumstances

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24
Q

Slowly moving fluids are dominated by ?

A

viscous forces

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25
Q

when fluids are dominated by viscous forces, there is a low energy level and the resulting fluid flow is ?

A

laminar

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26
Q

In laminar flow, molecules of water follow smooth lines, called ?

A

streamlines

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27
Q

As the velocity of flow increases, the moving fluid gains _____.

A

kinetic energy

28
Q

relates the four factors that determine whether the flow will be laminar or turbulent, quantifies turbulence

A

Reynolds number

29
Q

Reynolds number formula

A

R = pqd/μ
where: R is the Reynolds number (dimensionless)
p is the fluid density (kg/m3)
q is the discharge velocity (m/s)
d is the diameter of the passageway through which
the fluid moves (m)
μ is the viscosity (kg/s.m)

30
Q

what does the Reynolds number imply

A

If R > 2000, then it is turbulent flow

31
Q

T or F: Turbulence in ground water is easy to detect

A

False. it is DIFFICULT to detect

32
Q

______ in ground water is difficult to detect.

A

Turbulence

33
Q

T or F: Darcy’s law applies only to slowly moving ground waters.

A

False: Darcy’s law applies only to VERY SLOWLY moving ground waters

34
Q

an imaginary line that traces the path that a particle of groundwater would follow as it flows to the aquifer

A

Flow line

35
Q

In a/an ________, flow lines will cross equipotential lines at right angles.

A

isotropic aquifer

36
Q

Steady-flow conditions may be solved by graphical construction of what?

A

a flow net

37
Q

a network of equipotential lines and associated flow lines

A

flow net

38
Q

The method of flow net construction is based on 7 assumptions, what are they?

A
  1. the aquifer is homogeneous
  2. the aquifer is fully saturated
  3. the aquifer is isotropic
    4.there is no change in potential field with time
  4. the soil and water are incompressible
  5. flow is laminar, and Darcy’s law is valid
  6. all boundary conditions are known
39
Q

3 types of boundary conditions possible

A
  1. no-flow boundary
  2. constant-head boundary
  3. water table boundary
40
Q

If there is recharge or discharge across the water table, flow lines will be ______ to the water table. If there is no recharge across the water table, flow lines can be ______ to it

A

at an oblique angle; parallel

41
Q

is a family of equipotential lines with sufficient orthogonal flow lines drawn so that a pattern of square figures results

A

flow net

42
Q

resisting force that acts tangentially to the surface of the solid

A

shear stresses

43
Q

resisting force that acts perpendicularly to the surface

A

normal stress

44
Q

resisting force that resists the movement of fluid molecules past each other

A

internal molecular attraction of the fluid itself

45
Q

shearing resistance is aka

A

viscosity

46
Q

what must be remembered when measuring water table level

A

make sure na stable siya inig measure, not directly after gikuhaan (static well level)

47
Q

how to calculate for hydraulic head

A

hydraulic head = surface elevation - depth to water

48
Q

how to calculate for pressure head

A

pressure head = depth of piezometer - depth to water

49
Q

how to calculate for the pressure at the tip of piezometer

A

P = hpg

The pressure at the tip of a piezometer = the height of water standing in the piezometer, multiplied by the density of the water in the piezometer and the gravitational constant

50
Q

how to calculate elevation head

A

elevation head = surface elevation - depth of piezometer

51
Q

how to calculate for vertical hydraulic gradient

A

vertical hydraulic gradient = total head / vertical distance between two piezometers

52
Q

As the velocity of flow _____, the moving fluid gains _____. Eventually, the ______ due to movement are more influential than _______, and the fluid particles begin to _______ in an _____ fashion. The result is a _____ flow

A

As the velocity of flow INCREASES, the moving fluid gains KINETIC ENERGY. Eventually, the INERTIAL FORCES due to movement are more influential than VICOUS FORCES, and the fluid particles begin to RUSH PAST EACH OTHER in an ERRATIC FASHION. The result is a TURBULENT flow.

53
Q

flow, in which the water molecules no longer move along parallel streamlines.

A

turbulent flow

54
Q

The inception of fluid turbulent flow in groundwater has been reported at a Reynolds Number ranging ______

A

from 60 to 600

55
Q

Experimentation has shown that Darcy’s Law is valid only when are such that the _____ forces of _____ predominate. These conditions prevail when the Reynolds number is ______

A

Experimentation has shown that Darcy’s Law is valid only when are such that the RESISTIVE forces of VISCOSITY predominate. These conditions prevail when the Reynolds number is LESS THAN 1 TO 10

56
Q

when the flow lines will cross the equipotentional lines at an angle

A

there is anisotropy in the plane of flow

57
Q

what dictates the angle flow lines will cross equipotential lines in there is anisotropy in the plane of flow?

A

dictated by
1. the degree of anisotropy and
2. the orientation of gradient (h) to the hydraulic tensor ellipsoid.

58
Q

rare reynolds number for groundwater

A

R > 1000

59
Q

what kinds of waters is turbulent flow common

A

surface waters

60
Q

when is groundwater turbulent

A

R = 60 to 600, in cavernous aquifers with surface inputs and cave outlets, but rare in sand gravel and silt aquifers

61
Q

boundary where Groundwater cannot pass

A

no-flow boundary

62
Q

boundary where the head is the same everywhere, represents an equipotential line

A

constant-head boundary

63
Q

boundary for unconfined aquifers

A

water table boundary

64
Q

aka (potentiometric) piezometric surface

A

water table boundary

65
Q

full NIA

A

national irrigation authority

Hydrogeology (6 decks)

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