Abstract
A numerical model has been made for the solution of phreatic surface seepage (single-phase fluid flow), assuming continuity of flow between unsaturated and saturated soil zones. It allows for continuous variation of the hydraulic properties as a function of the pressure head using real soil data taken from relevant literature. Soil anisotropy and layering, one-, two-, or three- dimensional problems, seepage faces and hysteresis can also be handled. The computer code based on this model has been validated in comparison with analytical, experimental, field and numerical results found in the literature. The impact of several factors on the accuracy of the results has been investigated. The various methods for the mathematical simulation of the hydraulic properties are shown not to influence significantly the numerical results. Conversely, not all hysteresis models performed equally well in all situations. Slight improvement was achieved using lumping of the time-dependent matrix. Extensive comparisons have been made between the writer’s model results and those derived by other methods, used for phreatic surface seepage solutions. Such methods usually ignore flow in the unsaturated zone, or make oversimplifying assumptions about the hydraulic property variation in this zone. The comparisons were based on dam, trench drainage and local or regional pumping problems. Case studies of pumping have also been made, and the writer’s model has been applied to the simulation of groundwater level changes in inner cities (with particular reference to London). It has been shown that the results derived using the various methods may differ significantly, especially in transient seepage analyses. Ignoring hysteresis may also lead to significant discrepancies with observations. Realistic modelling of the hydraulic property variation in the unsaturated zone was demonstrated to be of major importance. It is claimed that, overall, the writer’s model has been able to produce improved results compared with other methods investigated herein.