Fig. 4 Response surfaces in the –K_s plane obtained by means of a single set of error-free measurements of (a) pressure head, (b) water storage, and (c) tracer travel time. Other parameters include: _sk = 0.4, _rk = 0.05, _k = 12 m^-1, K_sk = 2.8 x 10^-5 m s^-1, and q = 1 x 10^-6 m² s^-1. Subscript k stands for the true value of the corresponding parameter