Unconfined aquifer =
Aquifer with free water surface as upper boundary (water table/phreatic surface) at which P = atmospheric
Confined aquifer =
Confined b/w 2 aquitards/cludes = P in aquifer everywhere greater than atmospheric
Valley aquifers in temperate climates
Porous and permeable soil
Water table highest beneath hills
- infiltrates and builds up more further away from river
Groundwater drains to topographic lows (river)
Groundwater divide =
Catchment boundary
Q = 0
Valley aquifers in arid zones
Less rainfall, surface recharge ~0
Water table highest beneath valley (river bed)
Water infiltrates through river bed
Homogeneous =
Independent of position in geological formation K (x,y,z)=c(onstant)
‘space’
Heterogeneous =
Dependent on position in geological formation K(x,y,z) x=x c
‘space’
N.B. K = hydraulic conductivity
Isotropic =
Independent of direction
K x=x f(a)
N.B. K = hydraulic conductivity
a = angle b/w horizontal and direction of measurement
Anisotropic =
Dependent on direction
K = f(a)
K = hydraulic conductivity
Transversely anisotropic
Layered formation, K can be considered as having only horizontal and vertical components
Kx = Ky x=x Kz
Steady state flow in a confined aquifer, assumptions
and in an unconfined aquifer
Homogeneous aquifer i.e. K constant
S-S flow conditions i.e. Q constant and uniform
1D flow
Constant boundary heads
Steady state flow in an unconfined aquifer with recharge, assumptions
Homogeneous aquifer i.e. K constant
S-S flow conditions i.e. Q constant and uniform
1D flow
Constant boundary heads
UNIFORM AND CONSTANT RECHARGE
Steady state flow in a confined aquifer with unequal boundaries, basic gist
- Darcy’s Law
- Integrate both sides
- Use constraints
–> flow rate is linearly proportional to hydraulic head
Steady state flow in an unconfined aquifer with unequal boundaries, basic gist
- Darcy’s Law
- Integrate both sides
- Use constraints
N.B. A=Bh b/c H is not constant
Steady state flow in an unconfined aquifer WITH RECHARGE and unequal boundaries, basic gist
- Mass conservation focussing on the control slice
- Integrate dQ/dX = expression for Q
- = to Darcy’s law
- Integrate both sides w.r.t x
- Eliminate both constants with boundary conditions
- Substitute constant in 2’s expression for Q
- Rearrange
Steady state flow in an unconfined aquifer with WITH RECHARGE and equal boundaries
Think like with unequal boundaries but ho-h1 = 0 so first part of equation cancels
Per unit length B =?
1
“…water does not travel from the sea to the lake” x =?
0
Upper aquifer surface when CONFINED must be ? both water sources
BELOW (diagram)
