Built by a geologist
Aquifer Transmissivity Calculator
Aquifer transmissivity describes the rate at which water of the prevailing density and viscosity is transmitted through a unit width of a represented saturated aquifer interval under a unit hydraulic gradient. Its dimensions are length squared per time. For a representative horizontal hydraulic conductivity K and contributing saturated thickness b, the relationship is T = Kb. The same relationship can be rearranged as K = T divided by b or b = T divided by K. GeoMiner solves any one of the three quantities from the other two and converts among metres per second, metres per day, centimetres per second, and feet per day for K; metres and feet for b; and square metres per second, square metres per day, square feet per day, and U.S. gallons per day per foot for T. Every conversion is normalized through metres and days so mixed supported units remain dimensionally consistent. Transmissivity is not hydraulic conductivity under another name. Hydraulic conductivity is a property of the porous medium and fluid at the represented direction, scale, saturation, temperature, density, viscosity, fracture state, and test condition. Transmissivity integrates the represented horizontal conductivity across saturated thickness. Saturated thickness is not automatically total aquifer, formation, screen, water-column, or well depth. A borehole can include unsaturated material, confining beds, non-aquifer units, incomplete penetration, and intervals that do not contribute to the represented flow. In an unconfined aquifer, saturated thickness can change as the water table changes, so transmissivity can also change even if the material conductivity is treated as constant. In a layered aquifer under compatible horizontal parallel-flow assumptions, total transmissivity is the sum of Ki times bi for the contributing layers. An equivalent horizontal conductivity is that total T divided by total saturated thickness. A simple arithmetic average of layer conductivities is not valid unless the thickness weighting happens to make it so. Vertical flow through layers uses a different equivalent-conductivity relationship and must not be inferred from this horizontal T = Kb arithmetic. Dividing a pumping-test transmissivity by an assumed saturated thickness produces an equivalent horizontal K for the represented test interval and support volume. It does not establish a uniform material property,