Flood inundation and retention are key hydrological characteristics of floodplain wetlands. This study developed a methodology for regional estimates of potential floodwater retention under floodplain inundation from ecologically significant flood return periods by coupling remote sensing and geographic information system technologies with spatial hydrological modelling. The Macquarie Marshes in Australia were selected as the case study area. Time series of Moderate Resolution Imaging Spectroradiometer 8-day composite imagery were related to peak flows (Ml day−1) of the 1-in-10 return period. Inundation extent in corresponding images was detected using the modified normalised difference water index (mNDWI). The potential maximum soil water retention was derived using a spatial hydrological modelling approach, which is driven by the Soil Conservation Service Curve Number (SCS CN) method. Soil and land cover data were collected and intersected to determine spatial distribution of CN using ArcGIS. The CN-based retention capacity map was then integrated with an inundation extent map to delineate the spatial pattern of retention under inundation. The results have ecological implications in relation to the response of broad eco-types in wetlands. This study has proved that the integration of remote sensing, geographic information system and spatial hydrologic modelling can be used to provide essential information as inputs to the management of environmental flows in terms of sustaining ecosystem function, biodiversity and habitat suitability. Copyright © 2013 John Wiley & Sons, Ltd.