A LECTURES 1&2 Flashcards
Capillary Fringe
Region above water table where water rises due to capillary forces in the porous medium
Confining layer
goes over confined aquifer
Perched aquifer
unconfined, clay lens stops recharge straight down and forms one, normally not much water
vadose zone
unsaturated zone, above water table (includes capillary fringe)
Phreatic zone
saturated zone
Aquifer
a geological unit that can store and transmit water at rates fast enough to supply reasonable amounts to wells
unconfined aquifer
water is in contact with atmospheric pressure
confined aquifer
water under pressure due to weight of the upgradient water and confinement of water between impermeable layers
aquiclude or aquitard
low permeability layer
Porosity
=void volume/volume, effected by grain shape and packing
Effective porosity
porosity available for flow
Intergranular porosity
Between grains
Intragranular porosity
within grains, usually not effective
Clay
high porosity
low permeability
Limestone
low porosity
high permeability (due to fractures)
Secondary porosity
secondary dissolution or structural opening (fractures, faults, bedding planes)
Permeability
measures the transmission property of the media and the interconnection of the pores
good aquifers have
high permeability surrounded by low permeability units
q (specific discharge)
=Q(volumetric discharge or flow rate)/A
water flows from
areas of high head to low head
dimensionless hydraulic gradient
dh/dl
Hydraulic conductivity (K) units
velocity (ms-1)
Darcy’s law limitations
doesn’t take into account pore space so area used is much more that area that can be used by the flow
linear pore velocity
darcy’s law with ne (effective porosity) added in
intrinsic permeability
k=N(dimensionless shape factor)* d^2(grain diameter)
Definition of a Darcy
A cube of porous medium with sides of 1 cm length and a permeability of 1 Darcy will produce a flow rate of Q = 1 cm3/s for a pressure differential of P = 1 atm for a fluid with viscosity µ of 1 cP
lower limit of darcys
low pressure gradients or permeability
threshold grad to get flow
below certain grad -non linear
higher limits of darcys
high hydraulic grad
observed discharge is much less
laminar to turbulent as so permeable
