Effects of temporally correlated infiltration on water flow in an unsaturated-saturated system

Effects of temporally correlated infiltration on water flow in an unsaturated-saturated system were investigated. Both white noise and exponentially correlated infiltration processes were considered. The moment equations of the pressure head (psi) were solved numerically to obtain the variance and autocorrelation functions of psi at 14 observation points. Monte Carlo simulations were conducted to verify the numerical results and to estimate the power spectrum of psi (S (psi psi) ). It was found that as the water flows through the system, the variance of the psi () were damped by the system: the deeper in the system, the smaller the , and the larger the correlation timescale of the infiltration process (lambda (I) ), the larger the . The unsaturated-saturated system gradually filters out the short-term fluctuations of psi and the damping effect is most significant in the upper part of the system. The fluctuations of psi is non-stationary at early time and becomes stationary as time progresses: the larger the value of lambda (I) , the longer the non-stationary period. The correlation timescale of the psi (lambda (psi) ) increases with depth and approaches a constant value at depth: the larger the value of lambda (I) , the larger the value of lambda (psi) . The results of the estimated S (psi psi) is consistent with those of the variance and autocorrelation function.