B&C Groundwater fundamentals Flashcards
Potential Energy
energy stored in a system
Groundwater flow
mechanical process
flow forces must overcome friction between porous media and fluid
in groundwater the main sources of potential energy
position (GPE), and pressure
unsaturated zone potential energy
due to attraction between soil and water (moisture potential)
Piezometer
a borehole only open at the bottom
tell us the pressure at the opening
isotropic
material properties same in all directions
k is scalar
work done per unit mass
=acceleration * distance
hydraulic potential to hydraulic head
divide everything by gravity
z
elevation head- from datum to bottom of piezometer
p/(g*rho)
pressure head - from bottom of piezo to top of water in piezo
homogeneous
same properties in every location of the unit
flow in an anisotropic medium
flow is deflected away from the gradient direction towards the direction with least flow resistance
Piezometric surface
connects all points to which water would rise if piezometers were installed
unconfined aquifer this is water table
hieght determined by the hydraulic head
Artesian well
Piezometric surface about ground surface
Flow direct to equipotential head lines
perpendicular in an isotropic homogen aquifer
Flow net
the network of equipotential lines and flow lines belonging to a specific aquifer
flow net assumptions
homogeneous, isotropic, fully saturated aquifer & flow boundary conditions
no flow boundary
flow parallel to boundary
equipotential perpendicular to boundary
constant head boundary
flow perpendicular to boundary
equipotential are parallel to boundary
effective stress (sigma e)
portion of total stress not borne by the fluid
compressibility
strain/stress
beta
compressibility of water
alpha
compressibility of porous medium, rearrangement of grains
compressibility is inversely dependent on
grain size
why is k aquitard < k aquifers
aquifers can transmit water quickly so if water pumped out head will drop quickly in aquifers
compression much slower in aquitards
Transmissivity T
= bK
amount of water that can be transmitted horizontally through a unit by the full saturated thickness of the aquifer
Ground water induced compaction
thick sequences poorly consolidated sediments with interbedded aquifers and aquitards
storativity values
very small <0.005
spring discharge controlled by
input events e.g. lots of rain
shape of hydrograph controlled by
flow through different pathways that have different K and velocities
