How to Calculate Transmissivity

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The transmissivity of an aquifer is a measure of the quantity of water that the aquifer can transmit horizontally and should not be confused with transmittance, a measure used in optics. An aquifer is a layer of rock or unconsolidated sediments that can yield water to a spring or well. Transmissivity is typically used to determine the water that an aquifer can deliver to a pumping well. It can be calculated directly from the aquifer's average horizontal permeability and thickness.

The Steps

    Define hydraulic conductivity as the volume of water that flows through a 1 square foot cross-section of an aquifer under a hydraulic gradient of 1 foot per foot in a given period of time. the hydraulic conductivity is therefore measured in area of water per unit time.

    Define transmissivity mathematically. We have T = KhD where T is the transmissivity, Kh is the average horizontal conductivity and D is the aquifer thickness.

    Determine the units of measure for transmissivity. The horizontal conductivity is measured in length per unit time and the aquifer thickness is a length. The transmissivity is therefore measured in area per unit time, typically square feet per day.

    Expect a low transmissivity for a confined aquifer. These aquifers are generally completely filled with water and retard the movement of water out of the aquifer. Confined aquifers will have a very low transmissivity.

    Examine the range of actual transmissivity values. An aquifer from the Cretaceous age can have a transmissivity as low as 1,000 square feet per day, while a limestone aquifer from the Eocene age may have a transmissivity as high as 50,000 square feet per day.


About the Author

Allan Robinson has written numerous articles for various health and fitness sites. Robinson also has 15 years of experience as a software engineer and has extensive accreditation in software engineering. He holds a bachelor's degree with majors in biology and mathematics.