Susan. Lecture 2 Flashcards
What is the hydraulic head?
The elevation of water surface above the datum (length)
What is the equilibration time in a new well dependent on?
Hydraulic conductivity (K) of the surrounding substrate
How is hydraulic head measured?
In wells, plezometers or manometers.
What is the potentiometric surface?
The plane created by the movement of water towards regions of lower hydraulic head.
Why is the waterlevel in the manometer nearest outflow lower? Why are both manometers not equal?
Moving water has energy so difference in head is due to energy budget. The pipe is horizontal so there is no change in elevation energy. The flow is steady and the area is uniform so the speed and kinetic energy are constant however the reduction in head must be a result of a decrease in pressure as energy is lost to heat as water molecules are sheared.
What is the hydraulic gradient?
The rate that head height changes over a distance. No units so dimensionless.
What were Darcy’s findings from his experiments?
If Q is doubled then the Hl doubles also as twice as much emergy is used to drive the fluid through the sand, increase in pressure head. Hence head loss is directly proportionate to flow rate.
Varying the length of the sand column but keeping the same Hl between manometers leads to a decrease in Q. Loss of energy to maintaining pressure head causes slower flow.
Darcy also assumed that two cylinders together have twice the flow through twice the area
What is the equation for Darcy’s Law and what are the variables?
Where K is the constant of proportionality
Define Darcy’s Law
Darcy’s Law is that fluid will flow through a porous medium at a rate proportional to the cross sectional area through which the flow occurs, the hydraulic gradient and the hydraulic conductivity
What is hydraulic conductivity (K) dependent on?
The porous medium and the fluid viscosity
What is intrinsic permeability, k?
Is dependent solely on the medium and is independent of fluid properties
What is the equation for intrinsic permeability?
The unit for this is called the darcys
