Wetlands, particularly those in semi-arid or arid environments, are hotspots of biological diversity and productivity. Water resource managers are therefore increasing their efforts to conserve wetlands from environmental degradation. To do this, they require a thorough understanding of the wetting and drying regimes of these wetlands, and how potential land use, climate change and water resource development might affect inundation patterns. Hydrologic models can help to enhance this understanding, and to predict and assess future impacts. However, for semi-arid environments, data to assist in model construction is scarce. This paper presents a new method for developing a water balance model for a semi-arid wetland, the Narran Lakes ecosystem in eastern Australia. This method combines hydraulic (improving our understanding of water movement through a wetland) and hydrologic (improving our predictive capability for inundation levels) models and satellite imagery (acting as calibration and validation data) to produce a predictive model of wetland inundation. We show that this coupled hydraulic–hydrologic model yields inundation patterns commensurate with those that actually occurred over more than 30 years. The model results indicate that current inundation levels are at historical lows, which is most likely associated with a naturally occurring drought and increasing water resource development upstream.