The methodology of investigations for the determination of the hydraulic parameters necessary for initial inflow estimations are discussed. These include the methods of testing at depth for permeability, and data interpretation. The techniques of inflow estimation are described for shafts and drifts which are based upon advanced mathematical modelling of flow in multi-layered permeability sequences. For shafts, flow is approximated as being axisymetric about the shaft axis allowing the use of radial flow models. The reliability of steady-state analysis is discussed. As the geometric relationship between drift and the geological controls cannot be so simply approximated as in a shaft, the problem is essentially one involving three-dimensional flow. Due to the complexities involved in the three-dimensional modelling, the drift inflows are investigated using two-dimensional and radial models.