In recent years, sand-filled geotextile bags (geobags) have become a popular means of long-term riverbank protection. However, the associated failure mechanisms of geobag revetments are still not well understood. Three interactions influence geobag performance, namely, geobag-geobag, geobag-water flow, and geobag-water flow-riverbank interactions. To enhance the fundamental understanding of the performance of geobags in a revetment, a laboratory experimental program has been undertaken using both a fixed bed and a mobile sediment bed. In the experimental study, 600 bags were used to construct geobag revetments, and failure modes were observed for these two bed configurations. In general, there were some common trends for both bed configurations (i.e.,uplifting, turbulent bursting-induced flow through the revetment voids, overtopping, pulling out, and/or internal sliding), but in the mobile bed case, toe scouring had a significant negative influence on geobag performance. To extend the laboratory measured hydraulic parameters, the conveyance estimation system (CES) was used. A CES model was validated against fixed-bed experimental observations, and the validated model was then used to predict mobile-bed formations. The CES bed predictions were used to produce a failure diagram under geobag-water flow interactions and classification of bed formation under geobag-water flow-riverbank interactions. It is concluded that the CES can be a useful and computationally efficient tool for the prediction of hydraulic parameters and bed formations. In the next phase of the research, observations from the experimental program will be used to validate a discrete element model of a geobag revetment, which will be used to help develop much-needed geobag revetment design guidance. (C) 2013 American Society of Civil Engineers.