TOPOG is a terrain analysis-based hydrologic modelling package which describes how water moves through landscapes; over the land surface, into the soil, through the soil and groundwater and back to the atmosphere via evaporation. TOPOG is relevant to a wide range of water and land management issues, including: - waterlogging and dryland salinity - catchment water yield - stormflow runoff production - soil erosion and deposition - trafficability assessment - land disposal of treated effluent - forest establishment and harvesting - landslide hazard assessment - ecologic habitat assessment

Topog is primarily a research tool. It is designed for use by researchers and post-graduate students. It is ideally suited to studies of vegetation-water-salt interactions at small catchment scale, particularly in land-use change studies, or studies of climate change implications. It is also ideal for analysis of stormflow responses to intense rainfall events, and accompanying sediment transport. It is intended for application to small catchments (up to 10 km2), but given modern computer power, the application is more limited by the software's ability to accurately analyse the terrain from the supplied digital elevation data than by any particular size.

It is a complex, terrain based model, requiring a high degree of field data (or methods to estimate these), and knowledge of soil water transport processes, and (if vegetation growth is to be studied) of plant response to environmental drivers. We refer to TOPOG as a "deterministic", "distributed-parameter" hydrologic modelling package. The term "deterministic" is used to emphasise the fact that the various water balance models within TOPOG use physical reasoning to explain how the hydrologic system behaves. The term "distributed-parameter" means that the model can account for spatial variability inherent in input parameters such as soil type, vegetation and climate.

Topog has been used for a variety of analyses such as: - erosion studies, - waterlogging prediction, - stormflow and Hortonian flow/sub-surface flow partitioning, - catchment salinity, - agroforestry design, - plantation growth and impact on saline watertables - catchment yield and cimate change - transport of pollutants

TOPOG is a terrain analysis-based hydrologic modelling package which can be used to: - describe the topographic attributes of complex three dimensional landscapes - predict the spatial distribution of steady state waterlogging, erosion hazard and landslide risk indices - simulate the transient hydrologic behaviour of catchments, and how this is - affected by changing catchment vegetation - model the growth of vegetation and how this impacts on the water balance - model solute movement through the soil - model sediment movement over the soil surface TOPOG describes how water moves through landscapes; over the land surface, into the soil, through the soil and groundwater and back to the atmosphere via evaporation. Conservative solute movement and sediment transport are also simulated. The primary strength of TOPOG is that it is based on a sophisticated digital terrain analysis model, which accurately describes the topographic attributes of three-dimensional landscapes. It is intended for application to small catchments (up to 10 km2), but given modern computer power, the application is more limited by the software's ability to accurately analyse the terrain from the supplied digital elevation data than by any particular size.