Estimation of soil moisture and groundwater recharge using the TOPOG_IRM model

A distributed parameter ecohydrological model (TOPOG_IRM) was applied to a 1.6 km(2) pastoral catchment in southeast Australia for estimating soil moisture and groundwater recharge, for a period of 1992-1994. The main objective of TOPOG_IRM is to provide a realistic description of the key processes which control the soil moisture dynamics, evapotranspiration, and to investigate hydrological and ecological responses at a catchment scale. The model was not fitted but parameterised with field data and literature values. The soil moisture content at various depths was well simulated for six sites in the catchment representing different soil types and landscape positions. The spatial patterns of the soil moisture content appear to be controlled mainly by the soil types, and the results indicated that there is little lateral movement of water in the catchment. Average groundwater recharge was found to be 5% of the annual rainfall, and its spatial patterns were dominated by the soil types. The study has demonstrated potential application of TOPOG_IRM in simulating catchment scale responses under different land management options in the context of salinity control.