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Hydrology > Sub Surface Water > Flashcards

Sub Surface Water Flashcards

1
Q

What is groundwater

A

General - All water in the ground (vadose and phreatic)

Specific - water in the phreatic zone under water table

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2
Q

What is the vadose zone sometimes referred to as

A

Soil water zone

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3
Q

What is the importance of sub surface waters

A

Contaminant transport - how they get into the source. Might have industrial sites that leak chemicals.
Water supply - our drinking water from groundwater sources.

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4
Q

How much of Lancaster’s water is from bowland fells

A

1/3

Full of aluminium, iron and calcium

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5
Q

How much of Lancaster water is fr Lake District

A

1/3

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6
Q

How much of Lancaster’s water is coming from the river Lune

A

1/3

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7
Q

Where is experimenting on upward groundwater flow

A

NIREX in sellafield, Cumbria

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8
Q

What is nirex

A

Nuclear reactor in sellafield - hoping to pump it underground and by the time it reaches the surface again it will have decay to a safe level but might contaminate aquifer

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9
Q

What aquifer might NIREX waste contaminate

A

Triassic Sandstone Aquifer

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10
Q

How does water move through the subsurface

A

Through pores, fissures in the matrix

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11
Q

How do we measure pores

A

By the volume (REV) representative elementary volume

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12
Q

What units do we measure pores with

A

M^3 because it’s volume

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13
Q

What are the types of groundwater bodies

A

Aquifers
Aquitard
Aquiclude
Aquifuge

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14
Q

What are the UK aquifers

A

Chalk aquifer on west, limestone in north south, sandstone on west Cumbria coast - permic Triassic sandstone (18%)

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15
Q

What is an aquifer

A

Groundwater body that has two critical properties - transmit and store water. It’s both permeable and porous.

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16
Q

What is permeability

A

Flow of water under unit area and unit hydraulic gradient (Ks) saturated hydraulic conductivity to allow water through

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17
Q

What is porosity

A

Volume of pores or voice in a volume of soil or rock (eta) holds the water. Measured over pore volumes

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18
Q

What is an aquitard

A

Transmit and store only small quantities like Bowland Fell.

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19
Q

What is an aquiclude

A

Stores but does not transmit e.g clay rich drift and glacial till.

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20
Q

What is an aquifuge

A

Neither transmits or stores e.g granite and tiff

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21
Q

Where is a good place to put radionuclei

A

Under an aquifuge

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22
Q

What are the different types of aquifers

A

Confined and unconfined

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23
Q

What is a confined aquifer

A

Through hill there’s a type of block, water is under pressure here and if you drill a borehole down to the confined aquifer the water table will rise.

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24
Q

What is the pressure at pizometric surfaces

A
  1. At this point the aquifer isn’t confined and water table is the same as pizometric surface
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25
Q

Example of w confined aquifer

A

Part of the Triamic aquifer called Flyde Aquifer. Has bunter sandstone layer with Carboniferous strata at the side. Under pressure bc of glacial till stopping it rising

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26
Q

What is artesian

A

Pizometric surface above ground

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27
Q

Example of an artesian confined aquifer

A

London basin. Chalk confined by clay in a depression. Water rises through bore hole so pizometric surface is above ground causing the borehole to expel water in artesian aquifer

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28
Q

What is the pizometric surface in an unconfined aquifer

A

The water table

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29
Q

What is the water flow in saturated zone

A

Below the water table. Area of high energy to low energy

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30
Q

What flow is the loss of energy or the loss of what

A

Total potential

Total head

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31
Q

What Is the equation for groundwater flow

A

H=P+Z

Where H is totally potential P is pressure potential and Z is elevational potential

Total loss of potential

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32
Q

How to figure out dH in darcys equation

A

(P1+Z1)-(P2+Z2) = dH

Position 1 - position 2

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33
Q

What is Darcys equation

A

Q = A x Ks x dH/L

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34
Q

What is L in Darcys equation

A

Horizontal distance between measurement of H1 and H2

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35
Q

What is the hydraulic gradient

A

dH/L

36
Q

What is Ks

A

Permeability

37
Q

What was Darcys original experiment (1856)

A

Water flow through sands in public fountain in Dijon, water comes in bottom and going out the top and two places we measure p values and z values. Use manometers

38
Q

Where is p and where is z

A

P is above and z is below

39
Q

What is a petosometer (borehole is bigger)

A

A bit of pipe that goes in trouble and is only open to aquifer at bottom of pipe. A little bit of screen to stop soil and sand going into pipe. Amount of water that goes above the bottom or the pipe is the pressure potential.

40
Q

Where do you measure z

A

Height of pressure measurement to point above a datum

41
Q

How to measure pizometer water level

A

Datalogged borehole

42
Q

What does permeability equal

A

Saturated hydraulic conductivity

43
Q

What does permeability depend on

A

Texture.

Sand (50cm/hr) silt (0.3) and clay (0.0008)

44
Q

What is anything less than 0.002

A

Clay

45
Q

What is anything between 0.002 and 0.063

A

Wilt

46
Q

What is anything between 0.063 and 2mm

A

Sand

47
Q

What is anything above 2mm

A

Gravel then boulder

48
Q

Why is the texture not really important

A

The particles that make up the rock is cemented together in some way e.g lithification

49
Q

What is most important

A

The soil aggregation effects

50
Q

How does layering and fracture effect permeability

A

Not uniform so can see fractures and desecration cracks. Means you can’t just get size of soil particles to work out permeability as lots of other things in the world means it’s not predictable

51
Q

What must permeability be

A

Measured

52
Q

How to measure permeability

A

Corepermeametry - lumps of undisturbed soil or rock.

Borehole tests- boreholes installed into ground and use that to conduct test

53
Q

What are the ways of testing core permeatry

A

Constant head laboratory permeability.

Falling head laboratory permeability - hammer Ito ground.

54
Q

Example of falling head laboratory permeatry

A

Ring permeanetry - 10cm core of undisturbed core extraction

55
Q

How long did it take in Danum to do one ring permeametry test

A

8 hours

56
Q

Equation for core permeability

A

Ks = Q/A x L/dH

57
Q

How to work out Darcys equation using a ring permeater

A

P2 is at atmospheric pressure as bottom is open (0) . P1 is constant level of water at top of core. L is height of core. Q is to keep p1 constant and is flow going through core. A is area of core

58
Q

How to work out borehole tests

A

Pumping more to draw water table down around borehole. Observation bores. Slope is proportionate to hydraulic conductivity

59
Q

Why is permeability very spatially variable

A

Due to soil layering, different rocks and souls

60
Q

Borehole tests

A

Length between the two boreholes. Z is to top of pipe from bottom. P is pressure, how high water table went

61
Q

What is water in unsaturated zone often called

A

Soil water zone

62
Q

Why is understanding how water comes down into profile important

A

For studies in sellafield about radionuclei so nothing gets diluted or contain images

63
Q

How does radionuclide in deep ground water get dilute

A

By meteoric water (rain) and ground water

64
Q

Why are additional processes important

A

Bc or the change in water content and flow only in some pores

65
Q

What is soil water content always measured

A

Theta

66
Q

What are the ways of measuring soil water content

A

Mass wetness
Volumetric wetness
Saturation wetness

67
Q

How to work out mass wetness

A

Mass water/ mass dry soil g/g

68
Q

What is volumetric wetness

A

Volume of water/ volume of undisturbed soil. Dry bulk density

69
Q

What is saturation wetness

A

Volumetric wetness/porosity

70
Q

Different ways to measure soil wetness

A

Gravimetric mathod
Analogue
Troxler moisture gauge

71
Q

What is the gravimetric method

A

Taking undistrubed soil sample and sealing it, taking back to lab, drying it and weighing it

72
Q

What happens if you keep drying clay

A

You remove structure from water of clay so it keeps going down - not good

73
Q

What is the problem with gravimetric method

A

Disturbance of volume during extraction

74
Q

What are the analogue methods

A

Neutron moderation - neutron probe.
Put soil in and then calcium carbide and mix together. Will react and generate ethane gas and will turn the gauge proportional to amount of gase created.
Aluminium tube.
Radioactive source is lower into soil, fast neutrons bombard the large ions in the souls (H+) -> cloud of slow neutrons measured by BF3 defector

75
Q

Problems with neutron moderation

A

Not good at surfaces.
Radiative so cant leave it infield.
Needs regular checking against a water reference - not automatic.

76
Q

What is time domain reflectometry

A

Analogue method. Safe to leave in field. Put finger across the two cores and it sends a frequency across the cable. Switching between the two rods into the ground. The dialect constant you know the speed of the EM wave relative to that in the vaccuum. DC 80 if wet soil. 2-10 if dry. Saturation slows down the noise and the time increases.

77
Q

Problem with time domain reflectometry

A

The finger against the two rods is not a perfect connection generating a bit of noise that zooms back into the unit. Unit is generating the signal and recording the noise coming back.

78
Q

Howto observe infiltration below a teee

A

Observing vertical percolation by backfilling

79
Q

What is used in Danum

A

Simplified time domain reflectometry - sesnrice to soil type not just water content

80
Q

Effect of partial saturation on hydraulic conductivity

A

Lots of pores but some good at conducting water. Pores empty first are but like macro, root and cracks. Once they have drained the rate it water loss slows slow.

81
Q

What to measure Kunsat

A

Tension infiltrometer (allows restrict water movement by known amount. Sits on top of bit soil cores to create Kunsat curve.

82
Q

How to work a tensiometer

A

3 bits.
Empty pipe fill with water. Ceramic top at bottom of pipe where it connects to soil and some way of measuring the positive or negative pressure- sometimes a gauge.
If water table is above the top it’s positive if it’s below its negative.

83
Q

What can be connected to a tensiometer

A

A gauge but in field you can have a pressure transducer and connect it to a data logger

84
Q

What can tensionmetwrs be used to calculate

A

Flow in unsaturated zone and infiltration around trees

85
Q

What does higher H at depth indicate

A

Upward flow - evaporation

86
Q

What happens if drainage is dominating at the site

A

It’s a negative sign, positive if evaporation is pulling water to surface

Hydrology (9 decks)

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