WATER-TABLE DYNAMICS IN TILE-DRAINED FIELDS

We present a method for simulating water table dynamics in tile-draine d fields that are subject to intermittent precipitation or irrigation. A stochastic state equation for the water table height midway between drain laterals is obtained by adding a random noise term to van Schil fgaarde's deterministic drainage model. The random term accounts for d ynamics not modeled by van Schilfgaarde's equation, which is based on numerous simplifying assumptions. The continuous-discrete Kalman filte r is used to obtain an estimate of the time variation of the water tab le height, as well as the variance of the estimate. The method is demo nstrated using experimental data from the literature and is shown to h ave advantages over alternative approaches. Additional testing is nece ssary to fully assess the validity of the stochastic state equation an d the utility of the filtering procedure.