Study on the spatial and temporal behaviors of unconfined groundwater head-field in heterogeneous region

The spatial distribution of hydraulic head, namely "head-field", is estimated from a limited set of observed data, including the uncertainty which caused by both the complexity of groundwater behavior due to the heterogeneity of flow region and the insufficiency of measurement equipments. It is necessary for the precise analysis of the regional groundwater to evaluate quantitatively the uncertainty of head-field. The present study is directed toward tackling this problem from stochastic standpoint. The behavior of unconfined head-field in the heterogeneous flow region due to a rainfall is treated as the physical process in the random field, and the statistical structure of head-field is analyzed based on the physical principles of the subsurface flow. Firstly, the spatial randomness of water-table response to a rainfall is formulated as the head variance, taking the infiltration process in unsaturated zone into consideration. Secondly, the unsteady head variogram after the rainfall is theoretically derived by the perturbation expansion, and the spatial head distributions during the recession process are estimated from a limited set of point data through the geostatistical approach. And lastly, a new criterion for the parameter identification of the regional groundwater model is also proposed, which takes full advantage of the stochastic properties on the uncertainty of actual head behavior.