Soil water and groundwater III

Question 1

what physical characteristics does flow velocity depend on?

Answer 1

• slope of the water table
• permeability of the rock or sediment in aquifers

Question 2

what is an aquifer?

Answer 2

a permeable geologic unit that can transmit a significant amount of water under an ordinary gradient

Question 3

what is an aquiclude?

Answer 3

a geologic unit which does not transmit a significant quantity of water under ordinary gradients
aquiclude=confining layer

Question 4

what are the three most common aquifer types?

Answer 4

• unconfined aquifers
• confined aquifers
• perched aquifers

Question 5

what is unconfined ground water for an aquifer?

Answer 5

an aquifer with a lower barrier to movement caused by the presence of an aquiclude below, but no upper barrier which allows water to fluctuate over distances upwards
- has a water table and is only partly filled with water
- rapidly recharged by precipitation

Question 6

what is confined groundwater?

Answer 6

aquifer with a lower and upper barrier to movement as there is an aquiclude located immediately above and below the aquifer
- completely filled with water
- slowly recharged

Question 7

what is perched ground water?

Answer 7

occurs when an unconfined water zone sits on top of a clay lens or another quasi-impermeable lens, which separates it from the main aquifer below

Question 8

what is hydraulic head?

Answer 8

total amount of groundwater energy (elevation head +pressure head)

Question 9

what is the elevation head?

Answer 9

z is energy of height above the datum

Question 10

what is the pressure head?

Answer 10

h(p): height of water which would create a certain pressure

Question 11

what is the hydraulic gradient? and its equation?

Answer 11

change in total head over a given distance, I= delta h/ delta L
* from low to high hydraulic head so always negative

Question 12

what direction does groundwater flow in relation to hydraulic head?

Answer 12

groundwater flows in direction of decreasing hydraulic head

Question 13

what is Darcy’s Law?

Answer 13

states that the flux of water through a permeable medium is proportional to pressure differences or energy differences within that medium

Question 14

what is the Darcy’s law equation?

Answer 14

Q= - AK delta h/delta L

Question 15

what is the equation for Darcian velocity?

Answer 15

q=Q/A= -K delta h/ delta L

Question 16

what is the equation for linear velocity/pore velocity?

Answer 16

v= q/n(e)

Question 17

what does the Darcian velocity represent?

Answer 17

the average behavior of all water molecules, in macroscopic terms

Question 18

what is the problem with Darcian velocity?

Answer 18

it ignores the details of the movement of individual water molecules, it assumes that flow occurs across the entire cross-section

Question 19

how does linear velocity differ from Darcian velocity?

Answer 19

linear velocity takes into account the tortuous path of water molecules through an effective porosity value