Error of pressure estimation close to water table by different retention functions

Error of pressure estimation (EPE) was produced close to water table due to very high fluid pressure gradient and different retention functions. Generally, EPE depended on pressures distribution on both sides of water table, depth of node below water table and spatial increment. EPE may accumulate itself to a sizable scale and cause convergence and mass balance problems. In particular, numerical models with the van Genuchten model (vG model) always invariably result in negative EPE while those with the Gardner-Russo model (GR model) and the Brooks-Corey model (BC model) may also cause positive EPE. Under the GR model or the vG model, smaller alpha causes greater negative EPE. Under the BC model, shorter and longer capillary fringe may cause limited positive EPE and great negative EPE, respectively. Numerical models may often underestimate water table responses to infiltration into the fine clay while overestimate the responses into the coarse sand. It is essential and feasible to eliminate EPE by way of revising the potentials of block boundary nodes.