8.5.2 Determination of hydraulic parameters
For equilibrium equations（e.g.Thiem's equilibrium equation），the coefficient of permeability（k）is the only required hydraulic parameter.The coefficient of permeability can be obtained from laboratory constant head tests，falling head tests，empirical formulas，or pumping tests.
Nonequilibrium equations（e.g.Theis's and Jacob's nonequilibrium equations）require the coefficients of transmissivity（T）and coefficient of storage（S）.The coefficient of transmissivity of a confined aquifer equals the product of the coefficient of permeability and the thickness of the aquifer and is thereby a constant.If the pumping induced an unconfined aquifer far less than the thickness of an aquifer，the thickness of the aquifer can be assumed to be constant and one can obtain the coefficient of transmissivity accordingly.
The coefficient of storage of a confined aquifer，which ranges from 0.000 5 to 0.001，is about the same as the compressibility of the soil.The coefficient of storage of an unconfined aquifer is a little smaller than the porosity of a soil and ranges from 0.2 to 0.3.