Principles of Groundwater Flow to Wells Flashcards
Three energy that groundwater posseses
mechanical, chemical, and thermal
Three external forces acting on groundwater
molecular attraction, gravity, external pressure
two forces resisting the fluid movement of groundwater
shear stress
normal stress
stress acting tangentially to the surface of the solid
shear stress
stress acting perpendicularly to the surface of the solid
normal stress
the _____ of the fluid itself resist the movement of fluid past each other
internal molecular attraction
this shearing resistance is known as the ____ of the fluid
viscosity
a device used to measure liquid pressure in a system
piezometer
piezometer is a device which measures the pressure, more precisely the ____ of groundwater
piezometric head
what does the piezometer measure
the extent to which water level will rise against the force of gravity, or the pressure of the groundwater
t or f : the velocity of groundwater flowing in porous medium under natural hydraulic gradient is very low
T
it is equal to the pressure head (hp) plus the elevation head (z)
total head
formula for total head
h = z + hp
formula for hydraulic head
Hh = surface elevation - depth to water
formula for pressure head
Hp = depth of piezometer - depth to water
formula for elevation head
z = surface elevation - depth of piezometer
formula for vertical hydraulic gradient
Hg = Difference in total head / vertical distance between two piezometer
t or f: hydraulic head and total head are the same
T
groundwater flows in the direction of ______ hydraulic head
decreasing
The pressure at the tip of the piezometer is the ____
pressure = height of water in the piezometer x gravitational constant x density of the water
density variation in water is due to variation in
salinity
water level in well filled with water coming from a point in an aquifer and which is just enough to balance the pressure in the aquifer at that point
Point-water head
is the height of the column of fresh water in an aquifer which is just enough to balance the pressure in the aquifer at that point
Fresh-water head
formula for point-water pressure head
PWPH = PWH - Elevation head
formula for fresh water pressure head
FWPH = PWPH x Pp/Pf
formula for fresh water head
FWH = FWPH + Elevation head
Total mechanical energy per unit mass
Force Potential
driving impetus behind groundwater flow
force potential
Force potential energy is equal t the sum of ___, ____ and ____
kinetic energy, elevation energy, and pressure
force potential formula
hydraulic head x gravity
t or f: high hydraulic head means high force potential
True
t or f: hydraulic head increases in the direction of flow
F (decreases)
t or f: as groundwater moves it encounters frictional resistance between the fluid and the porous media
T
Groundwater is warmed slightly as it flows and ____ energy is turned into ____ energy
mechanical ; thermal
t or f: undermost circumstance, the resulting change in temperature is measurable
F (NOT MEASURABLE)
slowly moving fluids are dominated by
viscous forces
if viscous forces are dominating in moving fluids, there is a ___ energy level, and the resulting fluid flow is ____
low ; laminar
in laminar flow, molecules of water follow smooth lines called ___
streamlines
As the velocity of the flow increases, the moving fluid gains _____. Eventually the _____ forces are more influential than the _____ forces. The result is a _____ flow in which water molecules no longer move along parallel streamlines.
kinetic energy
inertial forces
viscous forces
turbulent flow
this relates the four factors that determine if a flow will be turbulent or laminar
Reynold’s number
formula for reynold’s number
R = pqd / mew
reynold’s = fluid density x discharge velocity x diameter of passageway through which fluid moves divided by the viscosity
if reynold’s value exceeds ____, it is considered to be a turbulent flow
2000
t or f: turbulence flow in groundwater is difficult to detect
T
the inception of turbulent flow in groundwater has been reported at a reynold’s number ranging from
60-600
600 reynold’s number in groundwater flow are present if
the aqufier is cavernous
t or f: Darcy’s law is valid only if the resistive forces of the viscosity predominates
T
Darcy’s law is valid if the reynold’s number of the flow is
less than 1-10
t or f: darcy’s law applies only to very slowly moving ground waters
T
an imaginary line that traces the path that a particle of groundwater would follow as it flows to the aquifer
flow line
in an _____, flow lines will cross equipotential lines at right angles
isotropic aquifer
in an anisotropic aquifer flow lines will cross equipotential line at ____
an angle
the angle of the flow line in an anisotropic aquifer is dictated by
degree of anisotropy
orientation of the gradient to the hydraulic tensor ellipsoid
a network of equipotential lines and associated flow lines
flow net
______ conditions may be solved by graphical construction of a flow net
steady-flow conditions
method of flow net construction is based on the following assumption
- aquifer is homogenous
- aquifer is saturated
- aquifer is isotropic
- there no change in the potential field with time
- the soil and water are incompressible
- flow is laminar, darcy’s law is valid
- all boundary conditions are known
three types of boundary conditions
no-flow boundary
water table boundary
constant-head boundary
boundary where groundwater cannot pass through
no-flow boundary
boundary where the head is same everywhere
constant-head boundary
boundary representing equipotential lines
constant-head boundary
boundary for unconfined aquifers
water table boundary
if there is recharge or discharge across the water table, flow lines will be at an _____ to the _____.
oblique angle
water table
if there is no recharge across the water table, flow line can be ____ to it
parallel
a family of equipotential lines with sufficient orthogonal flow lines drawn so that a pattern of square figures results
flow net
steps for making flow net
- sketch flow net system and identify prefixed equipotential and flow lines
- identify prefixed end positions of equipotential and flow lines
- draw trial set of flow lines
- draw trial set of equipotential lines orthogonal to flow lines
