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CIVIL 220 > Introduction to Groundwater > Flashcards

Introduction to Groundwater Flashcards

1
Q

Hydrogeology

A

The sub-discipline of geology dealing with the distribution and movement of water in the Earth’s crust

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2
Q

Common Applications of Hydrogeology

A
  • Extraction of water: drinking, irrigation, manufacturing
  • Dewatering: construction, quarrying, flooding
  • Contamination: industrial discharge, spills, leaks from buried tanks, infiltration of agricultural runoff
  • Assessment of extraction effects
  • Quantification and management of groundwater resources
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3
Q

What are aquifers

A
  • Saturated rock/soil layer/s forming a reservoir for groundwater
  • contains pores or open spaces to hold water
  • pores or spaces generally interconnected
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4
Q

Forms of aquifers

A
  • Unconfined
  • Confined
  • Semi-Confined (Leaky)
  • Perched
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5
Q

Unconfined Aquifer

A

the water table forms the upper boundary and is exposed so is free to rise and fall

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6
Q

Confined Aquifer

A

groundwater is isolated from the atmosphere by much less permeable layers (aquitards and/or aquicludes) and is subject to higher pressures than atmospheric pressure

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7
Q

Aquitard

A

layer &laquo_space;permeable than aquifer, not impermeable

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8
Q

Aquiclude

A

an impermeable layer (aquifuge if water-free)

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9
Q

Semi-Confined Aquifer

A

intermediate between unconfined and confined

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10
Q

Perched

A

discontinuous (in space and time) saturated conditions overlie unsaturated conditions

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11
Q

2 Categories of aquifer properties

A

Storage and Flow properties

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12
Q

What are the storage properties and what do they dictate

A
  • dictate how aquifers store and release water

- Porosity, specific storage, specific yield and storativity

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13
Q

What are the flow properties and what do they dictate

A
  • dictate how water moves through aquifers

- hydraulic conductivity, intrinsic permeability, transmissivity

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14
Q

Porosity

A
  • % of aquifer consisting of pore spaces (voids)
  • Larger pore space (more voids) = greater porosity therefore aquifer has greater water bearing capacity
  • provides indication of volume of water in aquifer
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15
Q

Permeability

A

capacity of aquifer to transmit water through pore space and is related to connectivity of pores

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16
Q

What are the 2 forms of porosity and what type of rock do they dominate

A
  • Primary porosity: pore space created during the formation of aquifer and they generally dominate in clastic sedimentary rocks
  • Secondary porosity: pore space formed through fracturing and/or weathering of aquifer after formation and generally dominate in non-clastic sedimentary and non-sedimentary rocks
17
Q

What is primary porosity controlled by

A
  • grain size (larger = higher)
  • grain shape (rounded = higher)
  • sorting (well sorted = higher)
  • cementation (less cement = higher)
18
Q

What is secondary porosity controlled by

A
  • degree of weathering (more = higher)
  • persistence of fracture (higher = higher)
  • spacing of fractures (closer = higher)
  • openness of fracture (greater = higher)
  • filling of fractures (less = higher)
  • connectedness of fractures (more = higher)
19
Q

Hydraulic head

A
  • Height above a datum, e.g. mean sea level, of a column of water that can be supported by the hydraulic pressure at a given point in an aquifer; units L
  • elevation to which water will rise in a borehole connected to a point in an aquifer under pressure
  • provides indication of the ground water flow direction
20
Q

Hydraulic gradient

A
  • Rate of change in hydraulic head (h) per unit of distance of flow in a given direction
  • Equates to slope of water table or piezometric surface
  • Provides indication of groundwater flow direction
21
Q

Groundwater flow

A
  • equipotential lines are contours of h and flow lines indicate flow direction in water table maps
  • Flow lines always move down i, i.e. from high h to low h
  • Steep to vertical i in recharge and discharge areas
  • Gentler sloping to horizontal i in between
  • Downward flow in recharge area
  • shallower groundwater has higher h so a downward i forces water down into the aquifer
  • Upward flow in discharge areas
  • deeper groundwater has higher h so an upward i forces water up out of the aquifer
22
Q

Flownet

A

set of intersecting equipotential lines and flow lines representing two-dimensional steady flow through porous media

23
Q

Darcy’s Law

A

Flow (Q) = - hydraulic conductivity (K) x are of pipe (A) x hydraulic gradient (dh/dl)

24
Q

Hydraulic Conductivity

A
  • The rate of flow through a unit cross-sectional area of a media under a unit hydraulic gradient; volume/area/time – units L/t
  • calculates rate of groundwater movement
  • not a measure of permeability
25
Q

Iso/Anisotropy

A
  • If K is independent of the direction of measurement at a point in a geologic formation the formation is isotropic
  • If K varies with the direction of measurement at a point in a geologic formation the formation is anisotropic
26
Q

Homo/Heterogeneity

A
  • If K is independent of the position within a geologic formation the formation is homogeneous
  • If K is dependent on position within a geologic formation the formation is heterogeneous
27
Q

Causes of anisotropy and heterogeneity

A
  • sedimentation: grain size and distribution; sphericity; nature of packing
  • stratification: bedding; lenses
  • structure: faults
28
Q

Groundwater Discharge calculation

A

calculated using Darcy’s law

29
Q

Darcy’s Law at a macroscopic level

A

−Qis defined as flow through 1m2 of aquifer, i.e. a unit cross-sectional area of saturated porous material−This area comprises voids and matrix
−vD(specific discharge or darcy velocity)not an accurate portrayal of true microscopic velocity of water along winding flow paths through voids
−Average linear velocity (v) greater; gained from knowing ne (effective porosity) of the aquifer material
−Accounts for flow through voids only

CIVIL 220 (9 decks)

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