Aquifer Transmissivity Calculator
Calculate aquifer transmissivity with our free science calculator. Uses standard scientific formulas with unit conversions and explanations.
Formula
Transmissivity (T) = K x b
Transmissivity equals hydraulic conductivity (K, in m/s) multiplied by aquifer thickness (b, in meters). The result in m2/s can be converted to m2/day by multiplying by 86,400. The Thiem equation provides an alternative: T = Q x ln(R/r) / (2 x pi x s), where Q is pumping rate, R is radius of influence, r is well radius, and s is drawdown.
Worked Examples
Example 1: Sand and Gravel Aquifer
Problem: Hydraulic conductivity K = 0.001 m/s, aquifer thickness b = 25 m.
Solution: T = K x b = 0.001 x 25 = 0.025 m2/s\nT = 0.025 x 86400 = 2160 m2/day\nAquifer class: High productivity\nEstimated well yield: 2160 x 1.3 = 2808 m3/day
Result: T = 2160 m2/day | High productivity | Excellent for municipal supply
Example 2: Fractured Limestone Aquifer
Problem: K = 0.00005 m/s, b = 40 m.
Solution: T = 0.00005 x 40 = 0.002 m2/s\nT = 0.002 x 86400 = 172.8 m2/day\nAquifer class: Moderate productivity\nEstimated well yield: 172.8 x 1.3 = 224.6 m3/day
Result: T = 172.8 m2/day | Moderate productivity | Suitable for small community
Frequently Asked Questions
What is aquifer transmissivity?
Transmissivity (T) is the rate at which water flows through a unit width of an aquifer under a unit hydraulic gradient. It equals the product of hydraulic conductivity (K) and aquifer thickness (b): T = K x b. Units are typically m2/s or m2/day. Transmissivity integrates the flow capacity of the entire aquifer thickness into a single parameter, making it more practical than hydraulic conductivity alone for predicting well yields and regional groundwater flow rates.
How is transmissivity determined from pumping tests?
Pumping tests are the most reliable method for determining transmissivity. The Theis method and Cooper-Jacob straight-line method analyze drawdown versus time data from observation wells during a constant-rate pumping test. The Thiem equation uses steady-state drawdown data from two observation wells at different distances from the pumping well. These field methods capture the integrated properties of the aquifer including heterogeneity effects that laboratory tests on core samples would miss.
What transmissivity values indicate a productive aquifer?
Aquifer productivity classifications based on transmissivity are: greater than 500 m2/day is considered high productivity suitable for municipal water supply; 50-500 m2/day is moderate productivity adequate for irrigation and small communities; 5-50 m2/day is low productivity suitable only for domestic wells; and less than 5 m2/day is very low productivity with limited groundwater potential. Alluvial aquifers often have transmissivities of 100-1000 m2/day, while fractured bedrock typically ranges from 1-100 m2/day.
How does transmissivity relate to well yield?
Well yield is directly proportional to transmissivity. A rough estimate is that sustainable well yield (in m3/day) is approximately 1.0 to 1.5 times the transmissivity value (in m2/day) for a properly designed well. Higher transmissivity means the aquifer can deliver water to the well faster, resulting in less drawdown for a given pumping rate. Specific capacity (pumping rate divided by drawdown) provides a field-based indicator that correlates with transmissivity through empirical relationships.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.
Is Aquifer Transmissivity Calculator free to use?
Yes, completely free with no sign-up required. All calculators on NovaCalculator are free to use without registration, subscription, or payment.