What's the difference between transmissivity and K?
What's the difference between transmissivity and K?
(OP)
Let me start out with a personal statement. I have prided myself in having been able to get through the subject of geology knowing little to none about the field of hydrology. Now that I am breaking out my old books, I am finding out why. I believe it is an intrinsically confused subject, with redundant terms and misplaced concepts galore. Nonetheless, it is a science I now need to know.
I am curious about the practical aspect of transmissivity. I noticed that the units used, GPD/ft are very close to hydraulic conductivity, GPD/ft*ft. Am I right in assuming that transmissivity is just the horizontal component of hydraulic conductivity, for water moving through an aquifer?
Thanks.





RE: What's the difference between transmissivity and K?
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RE: What's the difference between transmissivity and K?
You had to say "practical aspect", didn't you...
Horizontal hydraulic conductivity is essentially the coefficient of permeability of a medium, and it quantifies the capacity of the medium to transmit water. Units are that of speed (length/time). The higher the number, the more permeable the medium is. With some caveats, it's essentially the rate of flow of water through a cross-section of one square foot of the aquifer medium, under a unit hydrualic gradient.
Transmissivity may seem less a nebulous concept if you remember the following relationship, keeping units constant:
T=kb
where T= transmissivity
k= horizontal hydraulic conductivity
b= thickness of the aquifer
An example is helpful...
An aquifer with a horizontal hydraulic conductivity of 10 feet/day that has a saturated thickness of 25 feet would have a transmissivity of 250 feet^2/day.
or...
Same aquifer would have a transmissivity of 1870 gpd/ft.
"Gallons per day per foot" is also a typical unit for transmissivity. To convert between these two units of transmissivity, just remember a cubic foot contains 7.481 gallons, and divide or multiply by 7.481 as the case may be.
RE: What's the difference between transmissivity and K?
I have to admit, those units continue to be cloud-worthy to me. It seems much easier to consider movement in terms of length/time than [volume/time]/length.
Thank you again! Mental clarity is at a premium these days...