Beverly, C.R., Nathan, R.J., Malafant, K.W.J. and Fordham, D.P., 1997. Development of a simplified unsaturated module for inclusion in the US Geological Survey three-dimensional finite difference groundwater flow model MODFLOW. Proceedings of International Congress on Modelling and Simulation (MODSIM 97),  Eds. A.D. McDonald and M. McAleer, Modelling and Simulation Society of Australia, Volume 1, pp 288-293.

Development of a simplified unsaturated module for inclusion in the US Geological Survey three-dimensional finite difference
groundwater flow model MODFLOW

C.R. Beverly¹, R.J. Nathan¹, K.W.J. Malafant²and D.P. Fordham²

1_{Sinclair Knight Merz, Melbourne}
2_{Bureau of Resource Sciences, Canberra}

Abstract

This paper describes the development of an integrated saturated/unsaturated catchment model of salinity processes and its application to an irrigated and dryland district in northern Victoria. The model simulates a coupled surface water and groundwater system in which a lumped conceptual model is used to model one-dimensional movement through the unsaturated zone, and a distributed model is used to simulate two-dimensional groundwater flow. Movement of water through the unsaturated zone was found to be dominatedby macropore flow, and accordingly the classical matrix flow approximations described by the Richards equation were not used. Instead, a conceptual model of the unsaturated zone was developed to simulate soil infiltration, recharge to the underlying groundwater system, capillary rise and evapotranspiration on a daily time step for each active cell within the model domain. Sub-surface lateral flow between each vertical soil column is not permitted, though once in the saturated zone lateral flows are handled by the groundwater model. Salt movement through the profile is simulated using a mass balance approach, and separate