4: Groundwater Flashcards

1
Q

What is an aquifer?

A

Permeable unit which holds and transmits significant amounts of water

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2
Q

What is an aquitard?

A

Low permeability unit

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3
Q

What is an aquiclude?

A

Essentially impermeable unit

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4
Q

What is hydraulic head (saturated)?

A

The sum of the pressure & elevation head
P/pg + Z
(ignore velocity head as it is negligible)

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5
Q

In which direction does water flow?

A

From high to low hydraulic head

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6
Q

What is Darcy’s law in terms of:

  • total discharge?
  • specific discharge?
  • confined flow?
  • unconfined flow?
A
Q = -Ks.A.dh/dx
q = -Ks.dh/dx
Q/m = -Ks.b.dh/dx
Q/m = -Ks.h.dh/dx
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7
Q

What is specific discharge?

A

q = Q/A [m/s]

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8
Q

What is the horizontal head gradient?

A

dh/dx

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9
Q

What is the vertical head gradient?

A

dh/dz

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10
Q

What is a potentiometric surface?

A

h(x): the imaginary hydraulic line that a reservoir of fluid will ‘equalise’ out to

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11
Q

What does steady state mean?

A

dS/dt = 0

i. e. I(t) = O(t)
also: dh/dt = 0

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12
Q

What is the groundwater equation for confined flow (horizontal)?

A

S.∂h/∂t = T(∂^2h/∂x^2 + ∂^2h/∂y^2)

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13
Q

What is storativity (equation, units, definition)?

A

S = bSs [-]

Volume of water released per unit decline in hydraulic head per unit area

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14
Q

What is transmissivity (equation, units, definition)?

A

T = bKs [m2/s]

Rate at which groundwater flows horizontally through an aquifer

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15
Q

How do you derive the potentiometric surface h(x) from the confined flow groundwater equation (1D steady state with no source/sink)?

A
S.∂h/∂t = T(∂^2h/∂x^2 + ∂^2h/∂y^2)
S.∂h/∂t = 0, ∂^2h/∂y^2 = 0
d^2h/dx^2 = 0
dh/dx = c1
h = c1x + c2
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16
Q

What is the groundwater equation for unconfined flow (horizontal)?

A

Sy.∂h/∂t = K(∂/∂x(h.∂h/∂x) + ∂/∂y(h.∂h/∂y))

17
Q

How do you derive the potentiometric surface h2(x) from the unconfined flow groundwater equation (1D steady state with no source/sink)?

A
Sy.∂h/∂t = K(∂/∂x(h.∂h/∂x) + ∂/∂y(h.∂h/∂y))
Sy.∂h/∂t =0, ∂/∂y(h.∂h/∂y) = 0
d/dx(h.dh/dx) = 0
h.dh/dx = c1
∫h dh = ∫c1 dx
h^2 = c1x + c2
18
Q

What is specific yield (units & definition)?

A

Sy [-]

Volume of water released per unit horizontal area of aquifer per unit decrease in water table

19
Q

What is specific storage (units & definition)?

A

Ss [m^-1]

Volume of water released per unit volume per unit decline in hydraulic head